Dave Richards AA7EE

September 21, 2016

Greater Harmonic Suppression and a Narrower RX Filter for the SST20

My scratch-build of the Wilderness Radio SST20 has been a great success. I’m not a very active operator but I’ve had 18 QSO’s on it so far, running it into a horizontal loaded dipole (a Buddipole) at 25 feet. The furthest was Hawaii at about 2350 miles distant, followed closely by Midland, PA at about 2200 miles away, as the crow flies. I previously thought the output power was 2.25W, but it looks as if it’s closer to 1.5W. I’ll explain why in this post.

Ever since completing it, I had been having uncertainties about the low-pass filter on the output. I understand that spurious emission requirements had used to be a little more lax for QRP transmitters, specifying that for transmitters under 5W, spurious emissions needed to be greater than 30dB below the level of the fundamental emission. This is no longer the case, as the requirement is the same for all HF transmitters in the amateur service, and is found in 97.307 –

“(d) For transmitters installed after January 1, 2003, the mean power of any spurious emission from a station transmitter or external RF power amplifier transmitting on a frequency below 30 MHz must be at least 43 dB below the mean power of the fundamental emission.”

Although I am not set up to make spectrum measurements on transmitters, a very rough test using the S-meter of my K2 indicated that my SST was emitting a 2nd harmonic that, at best, was only a few S-points below that of the main signal, It looked very much as if I wasn’t even fulfilling the older requirement of a minimum of 30dB suppression of spurious emissions. Digging around on the internet a bit, I found this paper on the GQRP site, giving practical values for low-pass filters for 50 ohm systems for all the HF amateur bands that I thought should satisfy current requirements. The suggested LPF for 20M was this –

As well as greatly improving harmonic suppression over the original SST filter, the use of this LPF in the receive path also improves image rejection as the image, with this receiver, is on the high side of the VXO.

 

Fitting it into the same space that the previous 2-stage LPF had occupied was a tough call, but I managed it. I did have to break one of my own rules of decorum, and allow one of the toroids to be slanted slightly, so that the layout looked less uniform (Oh, the horror!) but I was happy that it fitted into the space at all. The yellow T37-6 toroids of the new LPF are easily visible in this close-up view –

The first thing I noticed was that despite careful peaking of C28 (at the output of the TX mixer), the output power as measured on my OHR WM-2 wattmeter was now only 1.5W. Given that the 28MHz harmonic was previously very possibly only 2 or 3 S-units down on the main emission, I’m thinking that a significant portion of the 2.25W I was measuring at the output before was 2nd harmonic energy (and perhaps some unwanted TX mixer products too). The good news was that listening to the 28MHz 2nd harmonic on my K2 now revealed it to not even register S1, when the fundamental at 14Mhz was S9 +40dB! That is an excellent result, and one that falls well within FCC requirements. I observed a very similar result with the VXO signal at 18MHz. My K2 doesn’t cover the unwanted TX mixer product frequency of 21.932MHz (VXO freq + 3.932) – at least not with full sensitivity, and I don’t have a general coverage receiver with an S-meter unfortunately, so I can’t check the level of that unwanted emission.

The levels of the harmonics emitted from the antenna jack now easily comply with FCC Part 97. Due to the previous harmonic level I measured, I’m thinking that a significant level of 2nd harmonic is being delivered to the input of the PA and being amplified, before then being attenuated by the LPF. It would be preferable for that harmonic to be filtered out before the PA stage, and I may take a look at doing this in the future. In his SST40, JN3DMJ added an extra stage to the bandpass filter after the TX mixer to increase the level of spurious attenuation. You can see it here, under the heading “Upgrading of the filters”. With a better BPF in place, it may be possible to get an honest 2 – 2.5W from the final, with all of that power consisting of 14MHz energy.

As if to confirm to me that all was well, the little rig gave me a brief daytime QSO with KD3CA in Midland, PA – 2200 miles away. Not bad for 1.5W into a detuned dipole with an SWR of nearly 6:1!

The other thing that I took a look at was the crystal filter on the receiver. I had used the values of C6, C7, C8 and C9 suggested by Rich K7SZ on QRP-L for a wider response than even the values given in the manual for a wider filter. The stock values give a particularly narrow filter, and not all users will want that. I changed the values to those given in the manual as a mod for greater width. Does the way I’m explaining it make sense? I was going from extra wide to moderately wide, so to speak. Here are AF response curves taken by measuring the AF response of the entire rig at the headphone jack. The program used was Spectrogram.

Using K7SZ’ “extra wide” values of C6, C9 = 47pF, and C7, C8 = 120pF (the red vertical marker is at 400Hz – the sidetone I use) –

and using the “stock mod values” from the manual, for “regular wide response” – C6,C9 = 68pF and C7,C8 = 180pF (the red line represents an aggregate of all the peak values taken over a 16 second period, while the blue line is a response in one instant in time) –

Not sure if I’ll decide to go narrower with the filter, or leave it as it is. I need to experience a few more contest weekends before making any further decisions🙂

On an entirely different tack, I have been using a new camera for the one photo in this post, and all the photos in the previous post about my SST build. It’s much lighter, and more compact than the camera I used for the photos in all the other posts on this blog. I’m still trying to decide whether the image quality is up to par for me. It’s a different lens, with a slightly wider focal length, a different sensor, and I’m using different software to process the images. I am not quite yet used to using this particular lens in order to “see” my subject the way I want, and so there are a lot of factors in deciding whether it’s going to cut the mustard for use in this blog. However, it’s a great and relatively inconspicuous camera for carrying around with me. Occasionally, I like to do what one might call street and candid photography, and it excels at that. This is one of the things I do when I’m not slaving over a hot soldering iron –

But, for the most part, I prefer taking photos of radios. They are very relaxed and compliant subjects, and don’t give me a hard time when I point a camera at them, unlike some members of the general public (gee, I wonder why they would do that).

I’ll get back on topic and talk about radio in the next post, I promise. In the meantime, as I am getting the “neither here nor there” figure of 1.5W of power out of my SST20, I turned the drive down to 1W, to make it a nice, even figure. I am looking forward to sending “PWR 1W” during QSO’s!

September 17, 2016

A Single Lever Paddle From QRP Guys

When building the SST for 20M, my plan was to kit it out with a paddle, battery, and an easily deployable antenna, and head for the hills. That’s still the plan. I don’t operate portable very often, preferring the comfort of the operating position in my small apartment, where I can make as many drinks and snacks as I want, and do it all with the company of my 3 kitties. Bliss! However, having just made a small, lightweight CW rig, I have to take it out in the field at least once in order to prove it’s mettle.

Currently, the only paddle I have is a Bencher, which is a bit too heavy and cumbersome to carry in my backpack for a portable set-up. There are some really neat portable paddles on the market, but I didn’t want to spend much, so settled on the idea of making one from PCB material, inspired by Wayne NB6M’s paddle, and KI6SN’s version, which was based on Wayne’s design. Two things happened to stop that idea in it’s tracks though. The first was that, nearing the end of building my SST, I was beginning to feel a bit lazy. Occasionally, when wading my way through a scratch-built project, I ponder how nice it would be to build a kit and give my brain a rest. At around the same time, I came across the website for The QRP Guys and realized I’d hit paydirt. They have a selection of small and low-priced kits for the QRP’er, including some small paddles made from PC board for very affordable prices. Perfect! The QRP Guys are Chuck Adams K7QO, Doug Hendricks KI6DS, Ken LoCasale WA4MNT, John Steven K5JS, and Dan Tayloe N7VE. Holy moly – that is some serious QRP starpower. I think we’d all be well advised to keep an eye on what these guys are up to.

QRP Guys ship out once a week on Wednesdays. With any small ham business such as this, where the owner/operators have many other things going on, setting expectations is an excellent idea. I decided on a single-lever paddle, and ordered it over the weekend. Later in the week, a small bag of parts arrived in the mail –

QRP Guys provide a scale for you to gauge how easy or difficult each of their kits is to build. On a scale of 1 to 5, with 5 being the most difficult, this paddle kit is rated as a 4. They do mention that some kits may also be rated as requiring what they term “expanded skills” – meaning, I assume, more difficult than 5. The rating of 4 for this kit makes sense. The PCB paddle parts need to be positioned fairly accurately. The way to do it is with a light tack solder in one point, re-adjusting until the exact positioning is reached, at which point you can commit with fully soldered joints. There are quite a few small screws, washers, and other small parts, so care, and a container to put all the small parts in are good ideas.

Here’s the final paddle. What a neat-looking little assembly –

A view of the underside –

This paddle is intended to be fixed to a panel, such as the side of a portable transceiver. I wanted it to be on a base, so decided to fabricate one from single-sided PCB material –

The cable is a cord from an old set of earbuds that came to an early end in the washing machine. It has a small molded 3.5mm stereo jack on one end, which is perfect for the task. It is held to the paddle base with a loop of twisted wire that threads through 2 holes in the base. At the point where it is secured, the cable was covered with 2 layers of shrink tubing. Luckily, the flexible wires in the earbud cord were insulated with heat-strippable enamel, so all that was necessary to remove the insulation was a generous gob of solder on the tip of the iron, and a few seconds, for the enamel to burn off –

You can’t see them, but there are 4 stick-on vinyl bumpers on the underside, purchased from the local Ace hardware store – the same type I used on the SST –

The copper is not lacquered, so if I take the same photo in a few months, it won’t look quite as shiny –

For size comparison, here’s the paddle with the SST20 and a pack of playing cards –

Despite the little stick-on feet under the base, I’ve found that the most comfortable way to send with this paddle is to hold it in my hand. This will work well for portable ops, when a suitable surface on which to place it might not be available. The lever is made from springy stainless steel. Doug Hendricks reminded me of an old tip for finding suitable flexible metal strips for making your own paddle, if you wish to do so. Just visit your local auto parts store and purchase a feeler gauge – the tool that is used for measuring spark plug gaps. It contains multiple flexible metal strips, of varying thicknesses (and degrees of springiness), so you can pick the exact one to suit your preference.

I experienced a small learning curve with this paddle. Firstly, I had never used a single lever paddle and secondly, I wasn’t used to the springiness of the lever, as most keys and paddles use stiff metal for the pivoting part. It doesn’t take long to get used to though. If you’re looking for a cheap and rugged paddle, this is a good value for the money. QRP Guys have both single lever and iambic paddles, with and without a base.

September 9, 2016

A Scratch-Build of N6KR and Wilderness Radio’s SST for 20M

Note – all links in this post open in a new browser window. It would be a good idea to clear your cache from time to time, to make sure your browser loads the latest version of this post. As an example, I just found an error on the schematic, and uploaded a newer, correct diagram.

I’ve been wanting to build an SST for a few years now. It’s a plucky little rig, with a lot of character. Designed by Wayne N6KR in the late 90’s, appearing as a full article in QRPp, and a kit sold by Wilderness Radio, it ignited the imaginations of a whole generation of builders for it’s combination of simplicity, performance, and willingness to accept modifications cheerfully. The review from Adventure Radio Society was quite positive. It is a VXO-based QRP CW transceiver, with a simple superhet receiver (SST = Simple Superhet Transceiver), and a TX that puts out up to 3W, depending on your choice of transistor in the final (it can be dialed down for battery-powered outings). It has very fast, clean QSK – so fast, in fact, that it feels as if I can hear the band all the time I’m sending (W6JL would approve). You actually listen to your own signal as you’re sending – there is no separately generated sidetone. The sidetone level does vary with the volume control, as opposed to being a fixed volume, but I only find this to be an issue when I have the AF gain all the way up, in which case I either quickly adjust the volume knob, or partially pull the earbuds away from my ears while sending. By the way, the sidetone on this little rig sounds really nice. It’s a feature which helps to make operating the SST an enjoyable experience.

QRP’ers loved their SST’s. There was a lively discussion about the minimalist rig on QRP-L, with builders reporting back on the frequency coverage and performance of their builds, with details of mods they were trying. The kit came with a light gauge unfinished aluminum enclosure. The raw-finish aluminum was a blank slate which invited many different creative solutions to the age-old question of how to show off your project. Some folk endowed theirs with professional-looking paint jobs, while others used dymo labels, or simply scrawled right onto the panel with a Sharpie® for that authentic home-brew look. All approaches worked admirably well. I saw one SST that had been painted with a US flag, and looked great. Some of them were taken out on the trail many times, and showed many knocks and scratches on the case which, of course, just made ’em look better still.

original

SST Kit Version – Image from Wilderness Radio

original1

SST Kit Version – Image from Wilderness Radio

JN3-bong;y modified his SST with 2 varacters for extra frequency coverage. He also added a speaker, and a spot button. Click on this photo to go to his site, and read more about his SST.

Koichi JN3DMJ modified his kit version of the SST40 with 2 varacters for extra frequency coverage. He also added a speaker, a spot button, and expanded the LPF for better filtering of the transmitted signal. Click on this photo to go to his site, and read more about his SST. He says that this SST is his favorite rig. He has made over 1300 QSO’s on it so far. Thank you for the permission to reproduce this photo and link to your site Koichi.

Recently, I decided it was time to build my own SST, only to find that I had missed the boat on a kit, as Wilderness Radio had discontinued it at some point in the recent past. I called QRP Bob on the phone, hoping that there would perhaps still be a board and/or enclosure available, but I was out of luck. In fact, it meant that I was in luck, as I would have to scratch-build one, and that’s a good thing.

There is plenty of documentation for this rig online. The initial write-up was in the Spring 1997 edition of QRPp, available from Chuck K7QO here. Note that the preceding link is a PDF of all 4 volumes from that year. The entire QRPp archive is also on Chuck’s site and accessible from the main page. Ken WA4MNT has a copy of the manual for the Wilderness SST kit on his site. Other essential documentation is the mods and information collected from QRP-L messages from 1997-2004, from Ken Larsen AL7FS, here as an HTML file, here as a text file, or here as a .doc file.

Mine differed just slightly from the original. Here’s my hand-drawn version of the schematic, reproduced here with kind permission of N6KR. Don’t rely just on the following schematic, as my drawing is a bit goofy. Best to refer to the original circuit diagram in the manual, and use mine to see how it differs –

 

Note – I do not recommend using the LPF comprised by C34, C35, C36, L2 and L3. Although it just met FCC specs at the time of release, it is very unlikely to provide enough filtering for this rig to meet current FCC rules regarding suppression of spurious emissions. For more satisfactory filtering, see my post here. 

Component designations (e.g. C27, R11 etc) are the same as in the schematic in the Wilderness Radio manual. There are 3 parts in the above schematic that do not have such designations – they were added by me (the series capacitor and resistor from pin 5 of U3 to ground, and the 1N5817 diode in series with the 10-16V DC supply line).

Differences between the stock SST and mine are –

1)  Inclusion of a series  diode in the supply line for polarity protection. I did consider using a P-channel MOSFET so as to avoid the voltage drop, but decided to go with a Schottky barrier diode. Some diodes of this type have a big enough reverse leakage current such that they are not effective in this role, but not so the 1N5817. It’s forward voltage drop is about 0.34V in transmit. I still don’t like losing that much, but it’s an improvement on the higher drop of a regular silicon diode.

2) The use of trimcaps in the RX and TX oscillators in order to place the received signal in the center of the passband, and to put the TX signal on the same frequency as the RX signal. I’m still about 20Hz off due, I think, to touchy trimcaps, but it’s close enough – until I get the urge to tweak and adjust again🙂

3) The use of 68pF capacitors for C19 and C20 instead of the 100pF values specified. With 100pF feedback caps, my VXO wouldn’t oscillate, so I swapped them for 68pF ones, and it sprang into life (thanks to LA3PNA for the help on that). It may well also have oscillated with 82pF caps, and that is an option if you want your frequency coverage to be a little lower.

4) An MRF237 was used for the final instead of a 2N3553. This substitution was suggested in the manual for higher output power, as the MRF237 has higher gain. If you want a cheaper and more modern alternative to the 2N3553, I’m thinking that a BD139 should work as a direct replacement. Joel KB6QVI just told me that W8DIZ has the 2SC5706 at 10 for $4, and I’m wondering how it would work in this application.

5) A Zobel network was added to the output of the LM386. Mine was unstable at high volume settings. A series capacitor and resistor from pin 5 to ground is very commonly used in these circuits, and the inclusion of these 2 parts tamed my instability immediately.

6) Alternate values of the capacitors in the crystal filter were used to widen out the response. The original values were reported to be giving a particularly narrow bandwidth of around 200 – 300Hz at the -6dB points. I wanted something a bit wider. There were several suggestions in the QRP-L archived discussions. K7SZ tried widening his SST20 out with the help of these suggestions, but it still wasn’t wide enough for him. He suggested the use of 47pF for C6 and C9, and 120pF for C7 and C8, which is what I used. Thanks Rich. A few builders went further, and implemented the ABX (adjustable bandwidth crystal filter) mod that was used in the Wilderness Radio version of the NorCal Sierra. EDIT – K7SZ notes in his ARRL book “Low Power Communication” that his mod brought the center frequency of the filter down too low for him on his SST30, so he ended up going back to the stock values. I have found that using the values of C7/C8 = 120pF and C6/C9 =  47pF that Rich suggested on QRP-L for his SST20, I set the sidetone at 400Hz ( a new thing of mine – I’m experimenting with lower than normal sidetone pitch), and the center of the filter passband was still about 20Hz lower, which I guess is pretty close. If you like higher sidetones though, you may be better off with one of the 2 sets of stock values in the SST manual. SECOND EDIT – I plan to tighten the response of the filter, by using the alternate values quoted in the manual. After using the SST for a while, I think my version is a little wide.

Although the SST didn’t come with a keyer, many users added their own, the Wilderness KC1 keyer and frequency readout being popular. At the time of writing, this is still available – the only kit that Wilderness still supplies. I decided that I wanted to build a keyer onto the same board as an integral part of my SST. I didn’t need much in the way of special features, my only 2 requirements of a keyer for this rig being that it will operate in iambic mode B, and that it has a speed pot – a feature I think of as essential. Changing speed on the fly during a QSO is tricky if the option is accessible only via menus, but a piece of cake if all you have to do is reach out and twist a knob. Perhaps I didn’t look hard enough, but the only freeware I found didn’t support a speed pot. I remembered how well the N0XAS Super PicoKeyer that Dar W9HZC had given me had worked, and a light went on in my head. Dale sells spare chips for his PicoKeyer Plus at $6 each. I purchased 4, used one in this rig, and saved the others for future projects. The manual on Dale’s site will give you the info on all the features of this keyer, and how to access them. The surrounding circuitry is simple (the genius is in the coding), so it was easy to incorporate into the SST –

The on-board keyer used a replacement PicoKeyer-Plus chip from Dale N0XAS

The on-board keyer used a replacement PicoKeyer-Plus chip from Dale N0XAS

The keyer uses a piezo transducer to announce the responses to command inputs made via the CMD pushbutton and the paddle. It would be possible to feed this audio into the AF amp of the SST so that it can be heard in the earphones, but I elected to fit a small piezo transducer on the edge of the board. I had intended to punch a small hole in the side of the case to make it easy to hear, but this appeared not to be necessary. Note that in the schematic, I have called it a piezo “buzzer”. It is actually a transducer, but allow me to explain. There are piezo buzzers available to which you apply a voltage, and the unit rewards you with a loud piercing tone, generated by an internal oscillator. Some of the units available are called piezo buzzers, but they don’t contain the audio oscillator – just a transducer, which is often sharply resonant at a specific audio frequency, to enhance the volume of the emitted tone. I bought a 5-pack of so-called “piezo buzzers” on eBay. They looked too small to contain an internal oscillator and I was correct – they consisted of just the transducer, which was exactly what was needed.

This build looked great when it started (as they all do🙂 ). A nice, clean board, with nothing but potential. As projects progress, I tend to become more anxious that in a single unconsidered moment during a late night soldering session, the iron will slip, the odor of burning plastic will waft into my nostrils, and all the hard work will be undone in a careless fraction of a second. In truth, there aren’t that many errors that can’t be corrected, but this early shot of the board was the best it ever looked! As with all my projects, all the Manhattan pads were MePADS (for IC’s) and MeSQUARES (for everything else) from Rex at QRPMe

If you compare the above photo to later pictures, you’ll notice that I ended up changing the layout of the front panel controls.

In the next picture, the AF amp and the VXO have been constructed, as well as the 8V regulated supply line. Temporary DC and headphone jacks were also connected, so the circuit can be plugged in to see if it works. The shielded cable that connects to the tuning pot was installed, but left longer than needed to allow for the final install in the enclosure. Not too much of the circuit had been built at this point, but it was already possible to test the voltages at the input and output of the regulator, as well as ensuring that the LM386 made a nice, loud noise when the input terminals were touched with a screwdriver (a highly controlled and accurate test🙂 ) The VXO was tuned in on a nearby receiver and tested for frequency coverage. With the 20M version, the VXO is in the 18MHz range, and by subtracting the IF of 3.932MHz from the highest and lowest frequencies it oscillates at, you can estimate the final coverage of the SST, and make adjustments at this stage if you wish. The discussions on QRP-L (which are linked earlier) contain a lot of info on tailoring the coverage, so I won’t repeat it all here, but your options involve using different varactors, connecting a second crystal in parallel with the VXO crystal, using different values of rubbering inductor, and adjusting the value of R5. I won’t explain how these all affect the frequency coverage and stability, as this is discussed at length in the QRP-L archive and also, to a certain extent, in the manual. There is plenty of homework reading to be done if you are thinking of building this rig!

Here’s another view, with the VXO in the foreground –

Suddenly, the product detector and BFO burst onto the scene. In the next shot, the 3.932MHz BFO crystal is the one closest to the camera, with the trimcap for centering the passband just behind it. I used 60pF trimmers, as that is what I had the greatest quantity of. Something a little smaller might have made the adjustment less touchy though. I’ll leave you to experiment, if you want to. Things are getting pretty exciting at this point, because when you a touch a wire or metal screwdriver screwdriver to pin 1 of the product detector IC U2, you hear honest-to-goodness atmospheric noise – a distinctly different sound from what you hear when touching the input of the AF amp IC. It’s instructive, not to mention really cool, to hear this progression in the sounds you hear, as you touch the inputs of stages closer and closer to the antenna, as the build progresses. If you have a signal generator, you can inject that into the circuit, and look at the output on a ‘scope. Don’t despair if you don’t have a full stable of test gear though – it’s important not to underestimate the power of touching and listening. Once you’ve done it a few times, you get used to knowing what sorts of things you should be hearing. See the curved red power wire that supplies 8V regulated to the BFO/product detector? You’ll notice in later photos that it was replaced with a different-shaped wire. It’s rarely possible to get everything right the first time you construct something, so one-off builds like this tend to morph somewhat as they progress. It’s OK to change things as you go along –

The next stage to construct was the crystal filter. Do you notice how, on the board for the kit version of the SST, the crystals for the filter were lined up with the short edges parallel to each other, so that the filter takes up a significant length of one side of the board? You usually see filters with the long edges of the crystals lined up parallel to each other. I don’t know why Wayne did it this way, but it did occur to me that with this physical configuration, the input and output of the filter are further apart than they would be with the more conventional placement pattern. Perhaps this was an attempt to decrease the possibility of filter blow-by? It seemed like a good idea, so I replicated it in my Manhattan copy. The crystals in the filter are not yet grounded in this next shot –

As far as matching the 3 crystals for the filter, I placed them into an oscillator circuit, and measured the frequency of oscillation. My cheap Chinese stand-alone frequency counter only had a resolution of 100Hz, but then I remembered that my K2 had a built-in counter with a 10Hz resolution, so I used that. I needed 5 x 3.932MHz crystals total – 3 for the filter, and the other 2 for the oscillators in the TX mixer and the BFO/product detector, so I picked the 5 that were closest in frequency. Out of that group of 5, I took the 3 closest and used them for the filter, while the other 2 were used for the local oscillators (but not the VXO, which required an 18MHz crystal).

To verify that the receiver is working, you’ll need to also build the antenna LPF, consisting of L1, L2, and associated parts. Without it, you won’t be able to peak the antenna input trimcap C1. Notice that if you touch the input of the crystal filter, the noise from the phones sounds much more restricted than when you touch the output of the filter. In fact, you can work your way back through the filter, with the rushing atmospheric noise becoming more and more restricted-sounding as you touch each stage of the filter with your metal screwdriver. These quick checks help to confirm that your project is pretty much on track. Adding the receive mixer means that the receiver is complete. After peaking C1 for maximum band noise, you should be able to receive off-air signals. Congratulations! If you substituted a trimcap for C10, you can also adjust it to place the received signal in the center of the passband, an adjustment that will depend on what pitch of sidetone you like to listen to.

My receiver didn’t work particularly well at first – I was getting very low audio out of it. One or two posts in the QRP-L archive made the same observation. I was beginning to talk myself into believing that the design was deficient in the audio department, and resolving to substitute a different audio chain, when I discovered that the coax which delivered the output of the VXO to the input of the RX mixer wasn’t properly soldered at the output of the VXO, resulting in low drive to the RX mixer. Re-soldering the joint solved the problem, and I can happily report that the audio output is more than adequate to drive a quality set of earbuds or a pair of reasonably sensitive headphones. If you attempt to drive a speaker, you will find that the level is only adequate for monitoring whether a frequency has activity or not, in a quiet room. That’s fine, as this was designed as a trail-friendly rig, with low current consumption in mind, and it certainly achieves that. VK3HN mentioned to me the idea of adding a lower noise AF chain designed to drive a speaker, and retaining the original AF output stage, feeding the inputs of both in parallel. The advantage of this would be that you’d retain the AGC action provided by the LED.

See the VXO in this next shot, with it’s 18MHz crystal? It has a total of just 10 parts, including the tuning potentiometer. I know that it represents old, well-established technology, but I feel that it still has it’s place in ham home-brew. Only 10 parts, and yet it has great stability and signal purity too. As long as you can deal with the fairly limited frequency range, a VXO is still a great choice as the frequency control in a simple rig –

This is always the point, when building a transceiver, where I slow down and spend some time playing with the receiver. I was dead chuffed, as we Brits say, that I had successfully built a little superhet receiver with a narrow crystal filter, that was sensitive, and sounded good.

But at some point, the momentum needs to be capitalized on before it is all gone, and so the build proceeded, with the addition of the transmit mixer. I also added the keying line (the green wires around the edge of the board) so that I could key the TX to see if it worked. If it did, then all that would be required would be to amplify the output of the TX mixer with the driver/buffer, and the PA. We were really getting close at this point! You’ll notice that there is a “channel” of space separating the crystal filter from the rest of the circuit. I did this for two reasons – firstly, as I thought it couldn’t hurt to physically separate the filter a little, to help prevent filter blow-by. Secondly, if there was excessive blow-by, it would give me enough space to erect a screen made from PCB material. C39, the 470uF AGC capacitor, is not present in this shot, nor in the later overhead notated view. I was planning on mounting it off the board, on the inside front panel, but eventually decided to mount it on the board. It ended up occupying the space between the AF amp and the edge of the board –

If you look carefully at these pictures, you may notice one or two components changing position slightly. As the build progresses, I will occasionally move a part or two in order to refine and improve the layout. I’m not going to point out which parts this applies to, as I don’t show these photos with the intention that you follow the layout closely. I started out by following the layout of the stages on the board from the SST manual but as the build progressed, realized I’d be able to move the position of the driver/buffer, thereby freeing up space for the on-board keyer, in one of the back corners of the board. Here’s another view of the board in the same state as in the above photo, with the receiver fully built, as well as the TX mixer. If you have a scope, you can measure the output of the VXO, which should be between 200 and 500mV RMS (that’s 0.565 – 1.414V peak – peak). You can also adjust C28 to peak the signal that will drive the buffer –

This was really the point at which I felt that I was home free. The TX/RX switching was working well, and the rig was putting out a small signal on the operating frequency in the 20M band. All that was left was to amplify it – and even if that didn’t work, I still had a cool little receiver and let’s face it – receivers are cooler than transmitters🙂

The next shot shows the rig fully built, with the exception of the keyer, with the board temporarily mounted in an enclosure. I ended up changing the layout of the front panel controls, which necessitated the use of another enclosure. In both cases, I used the LMB Heeger 143 enclosure in plain aluminum finish (they also have it in black and grey). I used an MRF237 instead of the 2N3553 in the PA, in order to provide a bit more output, and you can see that transistor, wearing it’s heatsink. To the right of the PA transistor is the orange top of R12, the drive control, and to the right of that is the LT1252 driver/buffer stage. The RF input to the LT1252 is carried by a single wire underneath the board. There are only 2 wires under the board – the one just mentioned, and a length of RG174 coax connecting the output of the VXO to the input of the RX mixer –

A view of the completed board, with the N0XAS keyer in the rear left-hand corner (which is actually the rear right-hand corner, if you are looking at the board from the front panel end). I mounted the keyer chip in a machined socket. I run as many of the control cables as possible underneath, and drill holes in the board for them to enter. I think it looks neater that way –

This next view shows the layout. I got carried away and labeled a few too many parts. The side of the board that faces the front panel is the left edge. As with the previous overhead anotated view, C39, the AGC capacitor, is not shown here, though it did end up being mounted on the board. Remember those SMD SA602’s I was giving away for the price of postage a while back (courtesy of KV7L)? I hadn’t used any myself, until now. 3 of them are in this little rig –

Time to get this thing in a case. The LMB Heeger 143 is an ongoing favorite of mine. It measures 4″ x 4″ x 2″ high, and has 2 small lugs at the front and back of the cover that engage with the front and back panels to prevent them from being pushed in. This feature adds rigidity and stoutness. One of the things I don’t like about most clamshell cases is that the front and back panels can be flexed; not so with this model. It comes in grey and a sort of black wrinkle finish, if you don’t want the raw aluminum. All the pots are Alpha brand. The 3 small ones were $1.29 each from Tayda. The larger tuning pot is also an Alpha part, but is very slightly smoother in action, and I wanted to optimize the experience of tuning this rig. It is Alpha part # RV16AF-10-20R1-B10K-LA (I got it from Mouser).  There is a small dummy load plugged into the back in this next shot, because I was having fun using the rig as a code practice oscillator🙂

This SST is quite a triumph for me, as it is the most complex project I have built so far with Rex’s MeSQUARES and MePADS.

The piezo transducer for the keyer was fixed to the edge of the board with a small spot of hot glue (on the high temperature setting of the hot glue gun, as it flows better) –

The keyer CMD pushbutton was a 22 cent cheapie from Tayda. These types are available with plastic and metal shafts. The ones with the metal shafts have a slightly smoother, more positive action. Get those ones. 4 vinyl bumpers from the local hardware store keep the SST from slip-sliding on my desk –

This enclosure is higher than the kit version, at 2″ high. I wasn’t initially planning on such a high case but the advantages are that it supports a larger tuning knob and, as you can see from the next shot, there is room for an internal battery pack, speaker, ATU or other add-on –

Here’s a view of the SST-20 upside-down and from the rear. From left to right – RF gain (rarely used), Antenna, DC power, and paddle –

I have a couple of spare covers for this enclosure, from projects that didn’t go as planned, and am thinking that it would be possible to have different covers with different accessories built in. For instance, one cover could have a speaker and extra AF amplifier, for operation at home. Another cover could contain a battery pack, for portable ops –

The red and yellow knobs look a bit garish, and I’m still getting used to them, but the thinking is that yellow = audio (AF gain and headphones), while red = keyer (speed pot and CMD button). It was also a way of using the cheap knobs I got from Tayda for 49¢ each🙂

So how does it perform? Well, in 2 words – very well. I don’t operate a lot, but I do spend a lot of time listening. I’ve had 6 QSO’s so far with a horizontal loaded dipole (a Buddipole) at 25 feet above ground at my home QTH. 3 of them were with stations in Colorado, about 900 miles distant, one with KE5AKL who was doing a SOTA activation in NM, also 900 miles from me, and one with a mobile station in Hooks, Texas, who was running 25W. He was 1600 miles away as the crow flies. The other was with a local station. The receiver is as sensitive as you’d need a receiver to be, and there’s a good amount of opposite sideband suppression. I haven’t measured it, but you only hear the opposite side of the signal weakly when tuning through a very strong station. The RF gain only needs to be backed down when in the presence of very strong stations, as the use of an SA602 in the front end can cause it to crumble under such circumstances. I haven’t needed to use it yet, and from what I’ve read, it doesn’t need to be used very often – hence the reason it is on the back panel. My frequency coverage, with an MV209 varacter, is approximately 14055 – 14064KHz, a swing of 9KHz, which is about as much as you’d want when tuning with a 1-turn pot. Many users mounted a switch on the front panel to switch in another varacter (usually an MVAM108, which was also supplied with the kit) to extend the coverage downwards. With the MRF237 in the final, my WM-2 wattmeter indicates an output power of about 2.25W with 11.61V at the input to the rig (11.27V after the polarity protection diode). When supplied with 13.8V from a PSU, the power output was about 2.8W. I didn’t measure the current consumption on transmit, but on receive it is between 26 and 27mA. This is low, but somewhat higher than the 15-16mA quoted in the manual. The keyer consumes <1mA, so that isn’t the reason for the difference.

The AGC LED is a rather unique feature. I’ll let you read up about it in the manual but for the addition of a few extra parts, it will save your ears from the worst ravages of sudden loud signals – and the LED is fun to watch too🙂 Most red LED’s have a forward voltage drop of about 1.7 – 1.8V. If you want to raise the AGC threshold, look for a red LED with a higher Vf – some of them go as high as 2.2V.

Although all the parts for this little rig are still available, a few of them are a bit harder to find than others. I purchased the LT1252 from Digi-Key – they have them in both through-hole and SMD versions. Chuck K7QO tipped me off to a supplier on eBay who was selling them in 10 packs. I couldn’t resist purchasing a pack. Thanks Chuck🙂 W8DIZ has the MPN3700 PIN diodes, though see the next paragraph for a worthy substitute.  There are several different choices for the PA transistor. 2N3553’s and MRF237’s were available on eBay when I was looking. Try to buy legitimate parts from a reputable supplier (my gut feelings seem to serve me well in this regard). I’m thinking that a BD139 would work in this position too. All the crystals are still available from Digi-Key. The part numbers are the same as in the SST manual, with the exception of X1-X5 for the 30M version. The manual quotes the Digi-Key part # as X007-ND. It is, in fact, CTX007-ND. Perhaps it changed. It has, after all, been 19 years since the kit was introduced!

Even though this design is now quite old, I think it is still very relevant. An experienced home-brewer can build this into a fairly small case, and take it on the trail with a simple tuner and, say, an EFHW, for a compact and effective portable set-up. All of the parts are still available, though it would be great to see a partial redesign, utilizing more modern and widely available parts. I’m thinking of a redesign of the buffer/driver and PA stages. BS170’s are cheap, and 3 of them in parallel, in class E, could provide close to the full QRP gallon. The original SST had room in the case for a 9V lithium battery, and could be dialed down to lower output powers to help battery life. Nowadays, newer battery technologies make more power available in a light and small package, so running 4 or 5W while portable with a small rig like this is practical. Kenjia JH1PJL used an NPN transistor in his driver, instead of the LT1252 IC. He also used a 1N4004 instead of the MPN3700 PIN diode (you can see pictures of his SST scratch-build here). In fact, all the diodes in the 1N4001 – 1N4007 series have the relatively slow recovery time of 30µS, giving them PIN characteristics. Any of them should work fine in place of the MPN3700. If a 1N4000-series diode is good enough for RF switching in the Elecraft K2 (the 1N4007), then it’s good enough for us!

Here’s a brief video of it in action, with a surprise appearance by Jingles the blind kitty. I fed her just before starting the video and forgot that her routine after eating, is to jump up on the desk to relax and digest her meal for a few minutes. I’ll work on producing a slightly better video, though videos are not my strong point. Apologies for the slightly crackly audio. It’s a combination of operator error and a camera that was designed primarily for stills, and not video –

The yellow knob was making me uncomfortable. It has since been replaced with a black one, and I am feeling much calmer now🙂

10 minutes later, and the red knob has now been changed for a solid and dependable black knob also. I finally feel that I know where I am in the world again🙂

For the near future, the next tasks are to –
a) add an extra stage to the LPF between the antenna and the rig for greater harmonic suppression and
b) tighten up the crystal filter a bit. I have decided that it’s just a little too wide🙂

July 1, 2016

Georges F6DFZ’s Very Stylish Homebrew Version of The Scout Regen Receiver

Several months ago, Georges F6DFZ sent me pictures of a Manhattan project he had just completed, using Rex’s MeSQUARES, and I have waited far too long to share it with you. It began life as a copy of the Ten Tec 1253 regen, but George said that the results and usability were very poor. One thing that must be said about regens is that the ones which don’t work well are very dispiriting. However, when you come across a good design and build it well, the performance can be very satisfying indeed. Luckily, Georges didn’t let his initial regen experience put him off, and he ended up turning the project into a receiver based on the Kitchin-inspired Scout Regen. He normally uses PCB software to design custom boards for his projects, but decided to try Manhattan construction for this receiver.

I like how his project was obviously the result of considerable careful planning –

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Now this is what I call planning! (Photo courtesy of F6DFZ)

The slow motion drive came from a very old French military surplus rig. George says that it tunes very smoothly with no backlash, and has 2 ratios – 10:1 and 100:1. The operator pulls on the tuning knob to shift to the slow tuning rate –

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The ex-military slow motion drive and dial (Photo courtesy of F6DFZ)

The front end is taken from the Scout regen. Georges added an RF preamp stage. You can see the RF board and tuning capacitor in this photo. I am guessing that the polyvaricon is for fine tuning –

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Rear view of Georges’ regen receiver (Photo courtesy of F6DFZ)

A closer view of that RF board –

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Photo courtesy of F6DFZ

From above –

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Photo courtesy of F6DFZ

The AF stage in the Scout design uses an LM386 with the ubiquitous 10uF capacitor between pins 1 and 8 for a stage gain of 46dB. While offering high gain with a low component count (and a low quiescent current), this circuit configuration also introduces a lot of hiss. Georges used a more complex, and lower noise audio chain. A MAX293 device provides 8th order low-pass filtering for good audio selectivity, and feeds an LM380 AF output stage. Using a relatively low noise device such as the LM380 makes listening much more pleasant, in my experience. Both my Sproutie and Sproutie MK II regens use one, and I regularly listen to them both for hours at a time. Good filtering, such as the arrangement that Georges has used, also does a lot to reduce unnecessary static and noise that can make listening for long periods fatiguing. Here are the AF stages, located underneath the chassis –

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AF Stages underneath the chassis (Photo courtesy of F6DFZ)

Another view of the topside of the chassis –

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Photo courtesy of F6DFZ

Georges also added an S-meter, which he got from a QRP book by Doug DeMaw –

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Photo courtesy of F6DFZ

This receiver operates on 80M and 40M. The band coverage on each band is 3.48 – 4.8MHz, and 6.95 – 8.5MHz respectively. Everything was done with hand tools, and a sheet metal brake which was made from an article in QST – this was indeed an admirably home-brew project! It even has dial lights –

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A real dial – with lights! (Photo courtesy of F6DFZ)

I love how Georges fabricated his own custom chassis from sheet aluminum, and paid attention to all the mechanical aspects of the design, making sure to include a dial and slow motion drive. These are the aspects of making your own equipment that can be very time consuming but which ultimately, make the project more enjoyable to use, and helps to ensure that it will occupy pride of place in the shack for years to come.

Incidentally, Georges wrote an article that appeared in the Oct 2014 issue of QST, on a CW adapter for the Collins KWM-2A transceiver. You can view it here if you have an ARRL membership. Thank you very much to Georges for being willing to share these pictures and details of his wonderful regen. I find it very interesting to see how other people build their projects, and I know a lot of others do.

February 10, 2016

The Muppet-Style Construction of John N8RVE

I have been meaning to write a post featuring the inspiring construction work of John N8RVE for almost a year now but sadly, am only able to think about one thing at a time, and The Sproutie MK II took up a lot of space in my head last year. Then, after finishing that, my one-track mind switched off from home-brewing and blogging activities completely. I am still unable to contemplate any more construction projects, and think that I may have done everything I set out to do with home-brewing, at least for a while.

In the meantime, there are a couple of things I’ve been wanting you to know about, and one of them is the excellent approach that John takes with his projects. John and I first became acquainted when he built a Rugster direct conversion receiver, and a WBR. Then I saw his build of a broadcast band regen, and that classic QRP design, Dave Benson’s SW+40, and really started to take notice.

John uses a form of construction that has been championed by Chuck Adams K7QO, in his QRP-Tech group on Yahoo Groups. Chuck calls it Muppet Construction and it refers to the practice of using an etched PCB, but soldering the components directly to the copper traces, thereby negating the need to drill holes in the board for component leads. It makes the process of creating the board easier, as there are no holes to drill. Also, after the circuit has been constructed, it is easier to look at the component side of the board and figure out what is connected to what – a process that is much harder with conventional through-hole PCB’s.

Back in January of last year, John finished construction of a broadcast band regen receiver, based on a design by Rick Andersen KE3IJ. Here is his very nicely etched “Muppet” PCB –

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BCB Regen Receiver (Photo courtesy of John N8RVE)

The board partway through construction –

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BCB Regen Receiver (Photo courtesy of John N8RVE)

And the completed regen (note the use of a rubber pinch wheel to achieve slow-motion tuning –

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BCB Regen Receiver (Photo courtesy of N8RVE)

John’s next project really caught my attention. It is the classic QRP design, Dave Benson’s SW40+. Dave has retired, and the SW40+ is no longer available as a kit (perhaps sometime in the future it will be again?) I’m sure there are many folk who would love to build a SW40+ but lament the lack of availability of a kit. Luckily, the kit manual, including schematic, is freely available online so the obvious answer is to build your own, which is exactly what John did. You could build it Ugly-style, Manhattan-style or, as John chose, Muppet-style. Here is his fully populated board –

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SW40+ (Photo courtesy of N8RVE)

Doesn’t this just look fantastic? This is very inspiring John!

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SW40+ (Photo courtesy of N8RVE)

Then, using the same technique, John built a HiMite 20. The HiMite 15 and 20 were next-generation QRP transceivers based on the Rockmites and, like the SW series of rigs, were the brainchild of Dave Benson. This is John’s version of the HiMite 20. When he first e-mailed me with news of this project, he was having some problems with the receiver. I’m not sure if he was able to solve the issues, but I think it looks great –

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HiMite 20 (Photo courtesy of N8RVE)

Just before his muppet construction odyssey began, John built a WBR, but ended up giving it to a friend who liked it. What to do? Build another one! This one is for the 31M broadcast band. John has had some issues with the volume level though otherwise, it is working OK –

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WBR Receiver (Photo courtesy of N8RVE)

One of the great things about developing the ability to scratch-build (as opposed to assembling projects from kits) is that you can pretty build anything you want, as long as you have the schematic. You can build it using any one of a number of techniques – Ugly Construction, Manhattan, Muppet, or any combination that you wish. You could even design your own PCB and take the drastic measure of drilling holes in it for component leads🙂

Thank you for sharing the details of some of your projects with us John, and I hope they inspire some readers the way they did me!

 

November 18, 2015

The Sproutie “SPT” Beacon – A Legal, Unlicensed HiFER Beacon

Note – this blog-post discusses the use of the 13553 – 13567KHz band under FCC Part 15 regulations in the US. Although it is a worldwide allocation, rules vary according to where you are. Off the top of my head, I do know that there are HiFER beacons operating in some countries on the European continent, but that is the extent of my knowledge of this type of operation outside the US.

Before saying anything else, I must note that even though the earlier projects which were named after my cats were not my designs, I did at least contribute enough of my own input that I could perhaps get away with naming them. I’m not sure that is the case with this venture, as I simply re-purposed it for a slightly different band and usage. However, the urge to name things around here after my cats is strong, so what I am calling The Sproutie Beacon, is really an original Hans Summers QRSS TX, modified slightly for the 15553 – 13567KHz HiFER band.

I have long been fascinated with clandestine and pirate radio stations. The UK has a long and hallowed history of pirate operation, since Radio Caroline and the other pirate ships began to grace the airwaves in the 1960’s. When I was in my teens in the 70’s, Caroline was still on the air, as was a newcomer to the pirate ship scene, a station called Laser 558. Laser 558 was, like the other pirate ships before it, stationed just outside British territorial waters, in international waters. It differed from the other pirates in one very noticeable detail though – it had American DJ’s, and was programmed like a US Top 40 station. To a British listener who was used to DJ’s talking quite a lot, the sound of American accents and near-continuous music, as dull as it might sound to a Stateside listener, was quite thrilling to these teenage British ears in the 1980’s. London is well-known for it’s many land-based pirate broadcasting stations on the FM band, but there weren’t too many outside the big cities. As a teen in the 80’s growing up in the Midlands, we did have a fairly high-powered pirate station on the AM MW broadcast band, with a wide coverage area, called Sunshine Radio, which I enjoyed listening to greatly.

When living in Los Angeles in the 1990’s, I was asked to DJ on a local FM pirate by one of the resident presenters, but politely declined, as I was already working in my chosen career, doing DJ, voice-over and production work. I was getting my DJ jollies for about 50 hours a week – and getting paid for it at that point, so said no to an opportunity that a few years earlier, I would most likely have jumped at. Los Angeles was not known for pirate activity at all – the area was almost entirely devoid of it, but this one station was a notable exception. It was known as KBLT. The founder, Sue Carpenter, even wrote a book about it, called “40 Watts From Nowhere”. Written from her perspective, and relating the trials and tribulations of running a pirate radio station that was on the air nearly 24/7 out of her apartment in the Silverlake district of Los Angeles, it’s a good read for anyone interested in the subject of pirate broadcast stations.

Then, in 2008, after moving to San Francisco, I was tuning around the shortwave bands in CW mode from my apartment in Ocean Beach one day, and heard a series of dits on approximately 4096KHz, Further investigation revealed that it was one of a cluster of unlicensed (and not legal) beacons operating from various locations in the California deserts on various frequencies centered around ~4096/4077KHz and 6626KHz with powers of the order of a few 100mW’s. All of them operated from solar power. Some also had batteries and could transmit 24/7, while others had only solar panels and were daytime only beacons. Even Jason NT7S could hear one of them from his QTH in Portland, Oregon – propagation was good on a regular basis back then. There are a number of these beacons, most of them in the deserts of the south west. Some send dits at various speeds, some send letters in Morse code. There is also one that sends the ambient temperature in Morse. They are discussed, with reception reports, over on the HF Beacons forum at HF Underground.

If, from all of this, you conclude that I would still be interested in running some kind of pirate operation, you’d be partially correct. I say partially because, in truth, although I enjoy listening to the clandestine activities of others, I wouldn’t want to do anything that might, even in theory if not in practice, jeopardize my ham license. I’d love to take a QRP solar-powered HF beacon out into the desert and leave it there, sending it’s valiant little signal, day after day, year after year, and checking the online reception reports from time to time. It would be interesting to see how long it would last. I read a report from someone who did install such a beacon, and his description was quite lyrical. He described how, whenever he was out hiking, fishing, or otherwise enjoying the great outdoors, he would take his portable shortwave radio and listen out for his beacon, thinking of the little transmitter out in the remote desert, courageously sending it’s diminutive signal across the great expanses of wilderness. Very evocative stuff.

It turns out that there is a way to operate an unmanned beacon on the HF bands below 28MHz, and to do so legally. The details, in the US, are contained within the FCC Part 15 regulations. These are the regulations which set out the requirements for unlicensed transmitters, among them baby monitors, cordless phones, toy walkie talkies, garage door openers, WiFi and Bluetooth devices, to name a few. In much of the spectrum in which operation is allowed, the power limits are very low, though there are a few bands where the allowance is more generous. The band with the most easily-attainable DX potential is the 14KHz-wide ISM band centered around 13.56MHz. Power limits are specified not in terms of the device output power, but as a maximum field strength at 30 meters. Medical diathermy machines operate in this band hence, I presume, the reason for a field strength stipulation rather than actual power into an antenna. This band is also inhabited by RFID devices. If you listen, you may well hear a variety of odd beeps and carriers, particularly near the center frequency of 13.56MHz. The maximum field strength allowed under FCC Part 15 regulations is 15,848 microvolts/meter at 30 meters. Few among us have access to accurate field strength meters, but John W1TAG has written this very informative paper, in which he runs the calculations, and comes to the conclusion that 2.3mW into a ground plane, or 4.6mW into a dipole would produce the maximum allowed field strength. Now 4.6mW isn’t a whole lot of power, but the WSPR and QRSS folk will tell you that DX results can be had, even within those limitations. In fact, the beacon activity on this band is divided between folk who run beacons sending CW at speeds that can be read by ear, and QRSS transmissions. A few people do run grabbers on this band, and report the results. Beacon activity in this ISM band is a very niche pursuit, but there is a good discussion forum over at the Longwave Message Board. As the title suggests, this site was set up for LF operators, but there is HiFER discussion there too,

My first “proof of concept” at putting together a beacon for this band was to connect an N0XAS PicoKeyer in beacon mode to my Pixie 2 transmitter. With the PiicoKeyer, if you insert the prosign BN at the end of stored message #1, it will automatically repeat. Unfortunately, my older version of the PicoKeyer will not power up again in beacon mode if power is lost. This was taken care of in later versions, but it meant that I wouldn’t be using this particular version of the PicoKeyer in the final version of the beacon. My Pixie 2 put out about 170mW on it’s original frequency of 7030KHz when powered by 12V, but this dropped to an encouraging 5-10mW at 3.6V (3 x 1.2V NiMH cells in series).

For the final version, I wanted all the electronics to be on one single board. At that point, I was thinking about purchasing a PicoKeyer chip from N0XAS and building the keyer, Manhattan-style onto the same board as a Manhattan-built transmitter. Then I remembered the Hans Summers QRSS Transmitter that I had built a few years ago. After a brief flirtation and a lot of fun with QRSS on 30M, the board sat languishing in a box. A little experimentation showed that it would still work down to voltages below 5V, and with the drive trimpot, I figured I’d be able to adjust the drive to give an appropriately low output power. Even better was the fact that on the QRP Labs website, there were details of a mod by Aldo IW2DZX for altering the output from FSK to straight on-off modulation, which I happened to want with this beacon.

Getting the QRP Labs QRSS TX on the HiFER band was straightforward. A pack of 5 x 13.56MHz crystals was purchased from an eBay seller. I chose HC49/U crystals over the more popularly available HC49/S, as I have read that the former tend to pull over a wider frequency range, due to the crystal cut. Receiving this pack of crystals in the mail was exciting. Think of the possibilities!

Here’s the final schematic for Hans’ little beacon transmitter, modified for straight on-off keying, and with values appropriate for the 13553 – 13567KHz HiFER band –

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The jumpers on pins 5, 6 and 7 of the ATtiny13 are used for programming the sending speed. Refer to the original kit instructions for programming the speeds. Hans’ firmware allows 6wpm, 12wpm, and 6 QRSS speeds ranging between QRSS1 (1 second dits) and QRSS20 (20 second dits). The original schematic didn’t include the 3 x 10K pull-down resistors on these pins. I included them, as my TX wasn’t transmitting the selected modes. If these pins are left without pull-down resistors, then an unconnected pin might be incorrectly interpreted as “high” by the chip. The original circuit used a reverse-biased red LED to provide frequency-shift keying. This was removed, along with a 470K resistor and a “gimmick” capacitor, and a 2N3904 transistor, 22K resistor, and 0.1uF capacitor added to key the PA transistor. Also changed were the values of inductance and capacitance in the output low-pass filter. To cap off the mods, a 3.3V regulator was added. Because of the strict power limitations on this band, I wanted to ensure that the TX was running close to the maximum allowed power at all times, with minimal variation due to power supply fluctuations.

Although I modified my existing QRP Labs original QRSS transmitter, if you don’t have one to modify, you could build it from the schematic above, Ugly-style or Manhattan-style. A little transmitter built using MeSQUARES and MePADS would look quite nifty, methinks. The values in the schematic are the final values for the HiFER band. If you decide (with the help of the info on Hans’ site) to build it for QRSS operation as an MEPT on a ham band, you can run it from 5 – 6V for increased TX power output. I believe it can put out up to 150mW. On the HiFER band, of course, we don’t want anywhere near that much power, so a 3.3V regulator does the trick nicely.

Here is a top view of the modified board, with both new inductor and capacitor values for the HiFER band, and the IW2DZX mod for straight on-off keying completed. The speed selection jumper holes to the right of the ATtiny chip have been drilled out to accept a header block. With the original TX, you had to solder a wire between 2 holes to select a given speed. Now, the speed selection is accomplished by plugging in a jumper block (or a combination of jumper blocks). You can also see the 3.3V regulator at the far left edge of the board, in the middle. 3 old parts to the left of the trim cap have been removed, and 2 new ones added. I’ll leave you to figure out what they are🙂  –

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The underside of the board, showing the extra transistor (a 2N3904) for the straight on-off keying mod. You can also see the 3 x 10K pull-down resistors, as well as a 1pF NPO capacitor added across the trimcap to tweak the frequency coverage.  The new values of capacitors required in the output low-pass filter were larger than I had on hand, so I made them up by placing smaller values in parallel. You can see 2 of those parts in the photo, placed on the underside of the board, in parallel with capacitors on the topside. I cleaned the board with flux cleaner, but ended up with a white residue. Not sure what it is. It bugs me, but I decided to let it go –

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A few more views of the board –

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If at this point, you don’t have a functioning keyer chip, you can verify that the transmitter is working by connecting pin 3 of the DIP socket to pin 8 (the +3.3V supply), which will activate the keying transistor and turn the PA on. You can listen to the little transmitter on a nearby receiver, or look at the output on an oscilloscope (or both).

Now to decide on a callsign, or other beacon ID that you want to send. There are no ID requirements when operating under Part 15 regulations. Indeed, this band isn’t even intended for these types of communications, though this usage does fall within the rules. This leaves you, the fledgling HiFER control operator, free to transmit any ID you want. I decided that I wanted the letters “SPT” in honor of my youngest kitty, Sprout. But how to go about changing the firmware? This was no mean feat for a person like myself, who has studiously avoided all types of non-analog electronics my entire life.

This next part of the narrative will be blindingly simple for many, but is directed at people like myself, who are fairly new to the task of compiling and flashing code to a micro-controller. You have to search around a bit to find this fairly basic information in a form that we newbies can understand, so I thought I’d attempt to provide a tutorial of sorts here. For those who know what they’re doing in this area, please feel free to add comments and correct me.

The code, written in C, is posted on Hans’ personal site here. The general page on the keyer chip on his site is here. By the way, if you haven’t seen Hans G0UPL’s personal site, you’re in for a treat. It’s a treasure trove of personal projects and just screams “home-brewer/experimenter”. There are many happy evenings of reading on it!

Somewhere online, (in a Yahoo group, I think), I read a message from Yan XV4Y to the effect that he hadn’t been able to compile Hans’ code, and had made a slight modification to it to correct that, as well as making an addition, to allow spaces to be included in the sent message. Later, Hans told me that he had been using Atmel Studio 4 on an older version of Windows, and that it was possible that some folk might have had trouble compiling it with newer programs. He also said that he wasn’t sure whether the code on his site had been updated or not.  I sent an e-mail to Yan, asking if there was any chance of him sharing his code with me. He responded very quickly in the affirmative, and also said it was fine for me to share it here. Please note that Hans’ code, as posted on his site, may very well compile and work fine. It’s just that I used Yan’s version. Yan was quick to point out that this is really Hans’ code with just a few minor mods from him. Many thanks to Hans for allowing me to post it here, and to Yan for allowing me to post his slightly modified version. For the slightly clueless people like me, the instructions at the beginning tell you what to do in order to insert your own custom callsign. For the record, Yan said that this code compiles perfectly on Mac OS X with Xcode using Crosspack-AVR. I’m a Windows person, so I’ll relate it the way I did it. In the following piece of beacon code, I set the callsign to be GRC. If you’re a fan of grilled cheese sandwiches and bacon, the idea of a “grilled cheese beacon” might be appealing, hence the callsign GRC. I know it’s a bit corny, but it will suffice for this example –

// This is an amendment to the beacon program written by Hans Summers
// G0UPL. It adds the facility for a space character to be embedded 
// within the transmitted callsign character string
//

// To change the callsign string you have to :-

// alter #define MSGMAX to the length of the callsign string +1

// insert the callsign you want, ensuring each character is seperated by a space
// into the text between the curly brackets after int8_t msg[MSGMAX] ending the string with a _SPC

//  e.g. for AB4CDE 

// #Define MSGMAX 7


// int8_t msg[MSGMAX] = { A B _4 C D E _SPC };

// e.g. for PA5D M M 

// #Define MSGMAX 9

// int8_t msg[MSGMAX] = { P A _5 D _SPACE M _SPACE M _SPC };




#include <avr/io.h>
#include <avr/interrupt.h>

volatile uint8_t msgIndex;
volatile uint8_t timerCounter;
volatile uint8_t counter2;
volatile uint8_t audio;
volatile uint8_t key;
volatile uint8_t bit;
volatile uint8_t pause;
volatile uint8_t character;
volatile uint8_t speed;
volatile uint16_t callsign;
volatile uint8_t keyDelay;

#define PERIOD 6

#define A		0b11111001,
#define B		0b11101000,
#define C		0b11101010,
#define D		0b11110100,
#define E		0b11111100,
#define F		0b11100010,
#define G		0b11110110,
#define H		0b11100000,
#define I		0b11111000,
#define J		0b11100111,
#define K		0b11110101,
#define L		0b11100100,
#define M		0b11111011,
#define N		0b11111010,
#define O		0b11110111,
#define P		0b11100110,
#define Q		0b11101101,
#define R		0b11110010,
#define S		0b11110000,
#define T		0b11111101,
#define	U		0b11110001,
#define	V		0b11100001,
#define	W		0b11110011,
#define	X		0b11101001,
#define	Y		0b11101011,
#define	Z		0b11101100,
#define _SPACE  0b11101111
#define _SPC	0b11101111
#define _0		0b11011111,
#define _1		0b11001111,
#define _2		0b11000111,
#define _3		0b11000011,
#define _4		0b11000001,
#define _5		0b11000000,
#define _6		0b11010000,
#define _7		0b11011000,
#define _8		0b11011100,
#define _9		0b11011110,
#define _BRK	0b11010010,
#define _KEYUP	0b10000000
#define _KEYDN	0b10100000

#define MSGMAX 4
#define SHORTSTART 0
int8_t msg[MSGMAX] = { G R C _SPC };

uint8_t speeds[8] = {1, 2, 10, 30, 60, 100, 150, 200};
uint8_t dit[8] = {150, 150, 150, 150, 150, 150, 150, 150};
//uint8_t speeds[8] = {1, 1, 1, 10, 30, 60, 100, 200};
//uint8_t dit[8] = {150, 36, 30, 150, 150, 150, 150, 150};
// DIT 		SPEED	WPM 
// 150 		1		12wpm
// 150		2		6wpm
// 150		10		QRSS1
// 150		30		QRSS3
// 150		60		QRSS6
// 150		100		QRSS10
// 150		150		QRSS15
// 150		200		QRSS20
// 36		1		50wpm
// 30		1		60wpm

int main(void)
{
	DDRB = 24;
	
	TCCR0B |= (1<<CS01) | (1<<CS00);	// Prescale by 8
	TIMSK0 |= (1<<TOIE0);
	msgIndex = 0xff;
	
	sei();
	
	while(1);
	
	return 0;
}

ISR(TIM0_OVF_vect)
{
	audio++;
	
	if (audio == 1)
	{
		if (key) PORTB |= 0x08;
	}
	else
	{
		PORTB &= ~(0x08);
		audio = 0;
	}
	
	// 1500Hz here
	timerCounter++;
	
	if (timerCounter == dit[speed])
	{
		// 10Hz here
		timerCounter = 0;
		callsign++;
		
		if (keyDelay)
			keyDelay--;
		else
		{
			counter2++;
			if (counter2 >= speeds[speed])
			{
				counter2 = 0;
				
				if ((character == _KEYDN) || (character == _KEYUP)) 
				{
					key = 0xff;
					bit = 0;
				}
				else
				{
					if (!pause)
					{
						key--;
						if ((!key) && (!bit)) pause = 2;
					}
					else
						pause--;	
				}
				
				if (key == 0xff)
				{
					if (!bit)
					{
						msgIndex++;
						if (msgIndex == MSGMAX) 
						{
							msgIndex = SHORTSTART;
							if (callsign > 6000)
							{
								msgIndex = 0;
								callsign = 0;
								speed = 0;
							}
							else
							{
								msgIndex = SHORTSTART;
								speed = (PINB & 0x07);
							}
						}
						
						bit = 7;
						// Get character from message
						character = msg[msgIndex];
						// Look for 0 signifying start of coding bits
						while (character & (1<<bit))
						{
							bit--;
						}
					}
					
					bit--;
					
					if (character == _SPC)
						key = 0;
					else if (character == _KEYDN) 
						key = 1;
					else if (character == _KEYUP)
						key = 0;
					else
					{
						key = character & (1<<bit);
						
						if (key) 
							key = 3;
						else
							key = 1;
					}
					
					if ((character == _KEYDN) || (character == _KEYUP)) keyDelay = 100;
				}
				
				if (key)
					PORTB |= (0x10);
				else
					PORTB &= ~(0x10);
			}
		}
	}
	
	TCNT0 = 156;
}

Copy and paste this code directly from here into a simple text editor, such as Notepad, if you’re using Windows. You can include the instructions at the beginning if you want – the compiler will know to ignore them. In the text editor, you can alter the code to include the callsign/message of your choice (no more than 8 characters, including spaces), then save it. You can name the file whatever you want, but make sure that the file extension is .c so that the compiler knows what it is.

Before compiling and flashing this code onto the ATtiny13 micro-controller, the other thing you will need to know is how to set the fuses on it. This beacon circuit uses an ATtiny13V, but I believe the ATtiny45 or ATtiny85 could also be used, as the only significant way in which they differ is that the later versions have more memory. The fuses determine basic operating parameters of the chip, and only need to be set once, though they can be reset, if you wish. After setting them you can re-flash the firmware as often as you like, and the fuse settings will remain the same, unless you purposely change them.

To find the fuse settings, you can use a fuse calculator such as this one. I used the default settings, with the exception that I disabled the internal divide-by-8 divider for the internal clock, and set the BOD (brown-out detection level) to 1.8V. The piece of code we are using assumes use of the internal 9.6MHz clock.  If you don’t disable the internal divide-by-8-divider, your keyer will send the code 8 times too slow. You can read elsewhere as to why the BOD level is set at 1.8V – try this page, under the heading “Brown-Out Detect (BOD). The resulting command line argument to set the fuses, as given by this calculator, is -U lfuse:w:0x7a:m -U hfuse:w:0xfd:m

The code for the beacon, as written in c, cannot be flashed to the ATtiny – the chip wouldn’t have a clue what to do with it. Before it can be flashed, the program has to be converted into a format that the micro-controller can recognize, through a process called compiling. It might be overkill to use such a big suite simply to compile a program, but Atmel Studio was the first free one I came across, and it worked, so I used it. Download the latest version of Atmel Studio (at the time of writing, it is version 7). It’s a big download – several hundred MB, if I remember correctly, so depending on the speed of your connection, it may take a while.

After opening Atmel Studio 7, select File>New>Project

A dialog box appears. On the left-hand side, under “Installed”, select “C/C+++” and then on the right-hand side, select “GCC C Executable project”. At the bottom of the window, you can name the project “grc-beacon” (or whatever you want to call it), and select where you want the generated files to be stored, unless you want to stick with the default location. Then click “OK”. Then a device selection box appears. You’ll want to pick ATtiny13, unless you’re using an ATtiny45 or ATtiny85. I haven’t tried the latter 2 devices, but believe they will work for this application. Then click “OK”.

You can insert your code where indicated, but at this point, I chose to completely delete everything that appears on this screen, and paste the code into the window. If you have already edited the code in a text editor to include your desired callsign, then no further changes will be necessary. If you are still using the code exactly as displayed on this page, you can at this point edit callsign “GRC” out and replace it with your callsign. Remember to also alter #define MSGMAX to match the number of characters in the callsign +1 (if a change is necessary). For the callsign GRC, that will be 4. If, for instance, you were using “DOGGIE” you would set it to 7. That’s it. Simple!

In the next step, we will generate the hex code that can be flashed onto the valiant little micro-controller chip in our beacon. Go to Build>Build Solution. As soon as you click “Build solution”, you should see all sorts of activity in the window at the bottom of your screen, as the compiler goes about the business of compiling the code. Hopefully, after the bottom window has finished scrolling, you should see –

Build succeeded.
========== Build: 1 succeeded or up-to-date, 0 failed, 0 skipped ==========

Then, towards the top right-hand side of your screen, in the solution explorer, after clicking on the little arrow next to the “Output Files” section, you should see the coveted hex file. Note that I called this project “grc-beacon-3” (I think the original version was called “grc-beacon” but this was my 4th attempt at getting it right) –

If you double-click on the hex file in the Output Files section, a new window will open up, and you’ll see the code in hexadecimal format. Mine looked like this. This is the code for the “grilled cheese beacon”🙂 –

Now you have the code in hex format, and the command line argument for setting the fuses. All that remains is to flash this onto the ATtiny micro-controller. SparkFun make a Tiny AVR Programmer that includes the target board for plugging in the ATtiny chip. I already had a USBTinyISP AVR Programmer from AdaFruit, so decided to make a target board, which cost me nothing extra, as I already had the parts on hand –

original

The ribbon cable that connects the AVR programmer to this target board can be inserted the wrong way, as the header connectors are not polarized. I opened up my AVR programmer and traced the pins from the ATtiny45 in the programmer to ensure that they would be connected to the correct pins on the ATTiny chip plugged into the DIP socket on the target board. Like goes to like, i.e. reset pin is connected to reset pin, MISO is connected to MISO, MOSI to MOSI, SCK to SCK, +vcc to +vcc, and gnd to gnd.

Here’s what my version looked like when finished (made with Rex’s MePADS). The thin strip of solder at the top left-hand side of the board in the next shot was put there as a visual reminder of which way to plug in the ribbon cable from the USBTinyISP –

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Here’s the target board plugged into the AdaFruit USBTinyISP –

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P.S. – when programming the ATtiny chips, I don’t fully insert them. With high quality machined sockets, a gentle push makes good enough contact, and makes it easy to remove the chip without deforming the pins. In fact, I did the same when plugging the chip into the beacon board and it has been running fine now for a few weeks. I do this in case I decide to reprogram the chip a few times before deciding on  the final callsign. Another way of treating the pins gently would be to use a zero insertion force (ZIF) socket when programming the chip. Tayda have them for a low price, or you could use this target board from John KC9ON, and his company, 3rd Planet Solar.

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The USBTinyISP Programming Adapter from 3rd Planet Solar. Photo reproduced with kind permission of KC9ON.

(Note – all my instructions here are for Windows. I know next to nothing about Macs, but if you’re a Mac person, the AdaFruit instructional linked below can help you out.)

AdaFruit have a useful instructional on how to use their AVR programmer, which applies to any USBTiny ISP. If you haven’t done this before, refer to their instructional, install WinAVR, and become familiar with it’s use. I’ll assume you know this stuff in the following paragraphs.

I burn the fuses first, in a separate operation. That way, I know they are set, and it makes subsequent programming operations simpler (with fewer things to potentially mistype at the command prompt). With the USBTinyISP plugged into your computer via a USB cable, as well as the target board, make sure the ATtiny13 (or ATtiny45 or ATtiny85) is plugged in to the 8-pin DIP socket on the target board, and you are ready to flash.

At the command prompt, navigate to the directory where your hex file is located. If it is on the desktop, for example, at the command prompt, you type

cd desktop

– and just to the left of the blinking cursor, you should see

Desktop>

– indicating that the Windows Desktop is the current directory. You’ll also see some other stuff to the left of the word “Desktop” but exactly what, will vary, depending on your particular set-up, so I won’t confuse you.

Just to check that your programmer is working, with it plugged into a USB port on your computer, type

avrdude

and you should get a list of all the commands that it recognizes. It should look something like this –

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Then, at the command prompt, type

avrdude -c usbtiny     

Then hit return, and because you didn’t specify the target part, the programmer will tell you so, and give you a long list of all valid parts. I’m not showing it here, because the list is too long to fit on the screen without scrolling but near the bottom, you’ll see the ATtiny13, and it’s abbreviation, which is simply “t13”.

Now that avrdude has slapped your wrist for not specifying the part, let’s give it what it wants, by typing

avrdude -c usbtiny -pt13  (or -pt45 if you are using an ATtiny45, or -pt85 for an ATtiny85)

Hit return, and you should get something like this, which indicates that your USBtinyISP is accepting commands, and recognizes the ATtiny device. In other words, it is ready to flash the firmware –

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Then to set the fuses, type

avrdude -c usbtiny -U lfuse:w:0x7a:m -U hfuse:w:0xfd:m

Hit return, and if you get something like the following, it means you have successfully written the fuses. Congratulations – you don’t have to do it again!

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If you want, you can set the fuses when you are flashing the hex file, but there is the potential to goof up, set the fuses incorrectly, and render the ATtiny incapable of further use. I’d rather do it in a separate operation and then not have to worry about it again.

Now to flash the beacon firmware onto the chip. At the command prompt, type –

avrdude -c usbtiny -pt13 -U flash:w:grc-beacon-3.hex

The above example assumes that your hex file is already in the directory that you have navigated to (in these examples, I have navigated to the Desktop), and that your hex file is called grc-beacon-3.hex  It probably won’t be called that, so make sure to substitute the name of your hex file. After hitting return, if you get something like this, you have hit the jackpot, and it looks like you are in business –

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If you have already built/modified the beacon transmitter, you can plug the ATtiny chip into it, and should hear the sweet sounds of your beacon ID being sent repeatedly on a nearby receiver (with a brief pause between ID’s). You can also connect a crystal earphone or other piezo-electric transducer to pin 2 of the chip to hear sidetone, as a check.

Tayda Electronics is now carrying a small range of enclosures, including some diecast ones, and they have great prices. I ordered a couple of sizes to see how they were, and ended up using the smaller one for this beacon. Here’s the board mounted inside it’s enclosure –

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That’s a small dummy load plugged into the BNC connector. Once connected, you can measure the peak to peak voltage across it with an oscilloscope, and use that to calculate the output power.

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Although you can’t see them, I fixed 4 little vinyl bumpers to the bottom of the case.

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Once you have this little powerhouse in an enclosure, you’re ready to set the output power with the 2.2K drive trimpot. Ideally, you’d be able to accurately measure the field strength at 30 meters from the antenna and use that as your yardstick. This is what K6FRC did when setting up his “FRC” HiFER beacon. IIRC, he runs 1.8mW into a groundplane. I saw an online posting from him in which he said that he was running very close to the maximum permitted field strength at that power level (he has access to a field strength meter). As I don’t have an FS meter, I chose to go with the results from W1TAG’s paper and chose 4.6mW into a dipole as my goal.

If you have an oscilloscope with a bandwidth high enough to measure voltages at such frequencies, it is a useful tool for measuring the output power of your beacon. As the power is specified in terms of the field strength it generates, there is no need to locate the transmitter close to the antenna feedpoint in order to minimize losses. If the regulations specified a maximum power out of the transmitter final, then this would be a worthwhile approach. This is the case with some Part 15 allocations (such as the one for the MW AM broadcast band). However, in this band, we are free to calculate the loss of the feedline and adjust the transmitter power accordingly.  This means that the transmitter can be located indoors, and away from the extremes of weather and temperature.

With my MFJ-259B, I measured the loss of my 50 feet of RG8-X at about 0.7dB, and figured that a transmitter output power of 5.4mW should result in about 4.6mW at the antenna. Using this online calculator, 5.4mW translates into a peak-to-peak voltage of ~1.47V into 50 ohms. With the 3.3V regulator in circuit, the maximum power output was only 10mW,so adjusting the drive to produce 1.47V peak-to-peak on the scope was fairly easy.

Incidentally, the backwave is very audible when you are close to the transmitter. The backwave is the carrier that is still radiated from the antenna when the keying is off. This happens because we are keying the final, so that when the key is “up”, some of the signal from the oscillator still leaks through the PA and into the antenna. I measured the backwave on this transmitter as 01.mW, and it remains at the same level regardless of where the output power is set. Granted that at lower output levels, such as 5.4mW, it is a greater fraction of the power when the key is “down”, but although I could hear the backwave in my immediate neighborhood, it gets lost in band noise pretty quickly. 0.1mW is about 34dB lower than 5.4mW, meaning that if someone is hearing the beacon at S9 +30dB, then the backwave will be a little over S8. Realistically though, anyone who is not really close to it will not be hearing the mighty 4.6mW signal at anything more than a few meager S-points at most, relegating the backwave into the noise. If it really bothers you, you could run the transmitter from a 5V regulator, set the output power higher, and then reduce it with an attenuator pad in the output circuit. That would lead to less backwave in the antenna. I didn’t bother about it.

Here’s the antenna – a Buddipole vertical element, mounted on a painter’s pole on the balcony of my house, putting the base of the L-shaped dipole at aobut 25 feet above ground level. The other element of the dipole is a length of wire. It’s a pretty good take-off to the north and east, but it is blocked by the house to the west and south –

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This is what the beacon sounds like on the K2 in my shack. I purposely took steps to reduce the signal level into the receiver, so as to get an idea of what it would sound like at a distance –

Here’s Mingus the neighborhood cat, listening to the Sproutie beacon on my K2, from across the street. Apologies for the cat butt! You can hear the backwave in this video –

The “SPT” Sproutie Beacon is now sitting in my shack, pumping it’s plucky little signal into the ether 24/7, and has received 2 “DX” reports so far. The first was from Jeff KF7RPI, who heard it at his QTH in Portland, Oregon, briefly at a 239 – 339, before it faded back into the noise. He is about 530 miles from me as the crow flies, which is pretty good for such a QRPp signal. The second report was from Bill Hensel on the LWCA message board. He was hiking in Pike National Forest when he heard SPT one day at 1845utc (also briefly) on his KA1103 portable receiver. Bill was about 900 miles distant from me, so that is also exciting. These are the only 2 reports SPT has received so far, but it is encouraging. Some folk do run grabbers on this band and look for QRSS signals. I’m thinking that if SPT’s 4.6mW signal can be heard at 900 miles while at 6wpm, it could go a lot further if it were sending much slower. However, I do like being able to decode it with my own ears, so will keep it at 6wpm (or maybe 12 wpm) for the time being.

Incidentally, if you want to put a HiFER beacon on the air with the minimum of fuss, the Ultimate 3S QRSS/WSPR transmitter kit from QRP Labs will operate on any frequency in the HiFER band, thanks to it’s Si5351 frequency synthesizer. The LPF for 20M should work fine for attenuating harmonics. As this kit is capable of producing far more power than Part 15 regulations allow, it is your responsibility to limit the output power if you operate this transmitter on the HiFER band. The Ultimate 3S will do multiple modes and bands – it’s a do-it-all-in-one MEPT, really, and at a very affordable price.

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If you hear the SPT beacon on 13558KHz, please send a report – either to the e-mail address listed on my QRZ account, or as a comment underneath this post. Reception reports will be very eagerly received. One gentleman in Seminole County, FL, reported that the area around the SPT frequency was a cacophony of noise in his area, and he stood no chance of hearing it. Those kinds of reports are useful too.  If you put your own HiFER beacon  on the air, do introduce yourself on the LWCA message board, and John can include you on the list of known active HiFER beacons.

original21

4.6mW of legal, unlicensed pluckiness and grandeur, hiding out in a diecast box.

November 11, 2015

A Few Manhattan, and General, Construction Pointers

Filed under: Amateur Radio,Ham Radio,homebrew radio,QRP — AA7EE @ 9:27 pm
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Someone recently left a comment on one of my older blog-posts asking if I could go into a little more detail about my construction techniques. It’s a question I’ve been asked a few times and although I have never detailed them in one post, if you were to read the posts for my main construction projects, you’d probably be able to glean enough info and links to pick up what you need. However, that information is scattered around this blog, so this post is an attempt to gather all the tidbits into one place. Please note that this is not a step-by-step “how-to” instructional, but more a collection of thoughts, tips, and links. It is a rough guide to how I do it, and not intended to be definitive. There are many ways to achieve a goal, and your mission is to find the way that works best for you.

I get my PCB material from seller abcfab on eBay. He has a good selection of different thicknesses of substrate, double-sided and single-sided, and even different thicknesses of copper. 0.06″ thickness is a nice stout board, good for enclosures, and also for Manhattan construction. The lesser thicknesses would probably only work for small enclosures, but would be fine for most circuit construction, unless you’re using a larger board and specifically need something inflexible (a thicker board would probably be more stable for a regen, for example). Up until now, I have used 0.06″ board for both enclosures and circuits, but a friend recently gave me some really nice pieces of thinner board (about 0.04″, I think), which I will use for building circuits on. When buying from abcfab, my standard order is for 0.06″ thickness, 1oz/ft² weight copper, single-sided, FR-4 substrate material. FR-4 is a composite of woven fiberglass cloth with an epoxy resin binder that is flame resistant (hence the FR designation). He also has a few different colors, which are fun for enclosures. I have bought red, blue, and the usual light brownish-colored boards from him. I did try to find a supplier for small quantities of other colors, such as orange, but the only way I found to do it was to buy whole sheets from a supplier and have them cut down to size, either for my own stash, or perhaps to also distribute to other home-brewers to spread the cost out a bit.

I won’t go into detail on enclosure building here, but I talk about my methods in this post. Ken WA4MNT has an excellent tutorial here. I learned most of what I know about building PCB enclosures from Ken’s tutorial. Ken uses shears to cut his material. I found that scoring it deeply on both sides with a box cutter allows it to be flexed and snapped cleanly. Running a file over the edge gives a nice result.

Anyway, a little about building circuits, which is the main subject of this post. Here are my main tools –

At the top is a 2.25mm crochet hook, used for winding toroids. I use the hook to pull the wire through the toroid, which is a great way of keeping the turns snug against the core. Beneath it, from left to right, is a tube of superglue gel. The gel form works best – the liquid is just too runny and gets everywhere. Next is a pair of round-nose pliers with round cross-section jaws (Pro’s Kit 1PK-29). I use these for bending component leads for the rounded look –

Round component leads on the Etherkit OpenBeacon

Next to the rounded pliers is a pair of green-handled Xcelite MS543J flush cutters with ESD-safe cushion grip handles, and a couple of small jewelers screwdrivers (from a cheap set bought from Radio Shack), which I use for scraping lacquer off the board in the places where Manhattan pads will be glued, as well as pressing down on the pads when gluing them to the board. Then a pair of Pro’s Kit 1PK-036S long nose pliers. I didn’t like the spring action, so I removed the spring from the handle. Next is a red-handled pair of needle nose pliers (cheap ones from Radio Shack). On the far right is a craft knife or as some call it, a box cutter. In the UK we call them Stanley knives, after the brand – in the same way that the British also call a vacuum cleaner a Hoover, and we in the US talk about Scotch tape, while the Brits refer to the same thing as Sellotape. This craft knife is used to deeply score both sides of a piece of PCB material before breaking it cleanly off. You’ll go through blades fast with this method. I bought a pack of 100 blades as typically, I find that every time I score a board enough times on both sides so that it can be broken off, I need to replace the blade. Blades are cheap when bought in bulk, and it’s not worth putting up with substandard cuts just in order to save a few pennies.

Looking at the needle nose pliers a bit closer, you’ll see that I filed flats into the ends. This has nothing to do with Manhattan construction. I needed a specialty tool to remove the nut holding a VFO encoder pot on a Yaesu FT-817, and found out that after filing a couple of flats in the jaws of these pliers, they fit the cutouts in the pot nut perfectly, allowing me to use the pliers to unscrew the nut –

The round-nose pliers in the foreground, and the needle nose pliers in the background.

I forgot to photograph my steel rules. I have 3 of them – a 12″ one marked in mm, a 6″ one also marked in mm, and an 18″ one marked in inches. They are used for scoring the lines in boards when cutting the PCB material and, of course, for all other kinds of measuring applications.

Moving along, at the top of the next picture is a T-handled reamer. This is used for making larger holes in chassis and enclosures. I start out with a drilled smaller hole, and enlarge it with the reaming tool. The brand name is General, and it is a No. 130. Then from left to right are a couple of files – a mill bastard, and a half-round bastard. The hand drill (and set of bits at the far right) is much used for drilling holes in enclosures. Finally, in the middle is a set of small files, which are very useful for finishing off all kinds of holes and rough edges. This particular one is made by General #707476 and is called a 6-piece Swiss Needle File Set –

When gluing Manhattan pads down, I first scrape the lacquer away from the board with a small jewelers screwdriver in the area where the pad will be glued. I know you’re not supposed to use screwdrivers for scraping things, but these were from a cheap set. I also roughen up the underside of the MeSQUARE or MePAD with a sharp craft knife blade to help adhesion. I put a small drop of superglue gel in the center of the area on the board where the pad will be, and lower the pad into position with the long nose pliers.

This next part is tricky. Once you begin to push down on the pad, you only have a few seconds before it is glued fast to the board. The trouble is, that as you push down on it (with a screwdriver or whatever other implement you’re using), the pad tends to slip around on the gooey gel, and change position. If you’re fast, you will have time to re-position it as it does this. You achieve this with a combination of pushing down slowly, and quickly re-positioning it by nudging it with the screwdriver. Once you start pushing down, the clock is ticking. You’ll have time to re-position the pad if necessary, but you’ll have to be fast! The good news is that if you do succeed in gluing the pad down in the wrong place, you can remove it and try again. Just wait a couple of minutes for the glue to set, then slide a sharp craft blade under the pad and pop it off the board. Be careful when doing this so that you don’t slice a finger, or slip and damage something else on the board. Once the pad is off, you can scrape away any remaining glue and go for a second try.

Component leads can be pre-cut and pre-formed with the cutters and pliers, and then placed against the pads and board to check the fit, before soldering. A few folk have asked how to actually get the parts standing up on the pads in exactly the position desired. This is the wonder of tack-soldering. Most modern components come with the leads already pre-tinned. For the purposes of tack-soldering though, it helps to have just a bit more solder on them. Once you have tinned the lead(s), you can place the part in the position you want it using a pair of pliers (or other tool), and temporarily fasten it in place with a bit of heat from your soldering iron. Then you can either tack-solder or permanently solder the other lead into place, after which you go back to the first lead and make that solder job permanent. As well as using pliers, I often use jewelers screwdrivers to coax leads into the right positions – use whatever you have, and whatever works for you. You’ll develop your own techniques over time. It can be a slow process, often taking many years, so don’t despair – enjoy the journey!

Oh, I forgot to mention the soldering iron. A temperature-controlled soldering station is preferred over a cheaper iron without temperature control. A temperature-controlled iron can deliver more heat when needed, such as when soldering to a circuit board ground plane. It’s surprising how much heat even a small ground plane on a circuit board can “sink” away from the tip of a soldering iron. The station I use is a Hakko 936. I don’t believe they make that model any longer, but there are plenty of affordable soldering stations available, for around the $100 mark. As for tips, chisel tips are good for most purposes. I use a 1/16″ chisel tip for most things, switching to a smaller 1/32″ chisel tip for the more fiddly tasks. The flat sides of a chisel tip will allow you to transfer heat more effectively to the area being soldered than will a conical tip.

Oh, and test gear. The most important piece of test gear by far, is a multimeter. I have a 20 year-old analog multimeter from Radio Shack, which used to be my main meter. Nowadays, I mainly use it for the times when I’m peaking circuits, when being able to see a needle move on a scale makes it easier to adjust a control for a peak or a null. My main meter now is a cheap manual DMM, an Extech MN35. It was a gift from my friend Antoinette last Christmas. IIRC, they are about $25 –

Most folk seem to prefer auto-ranging DMM’s. My preference is for a manual, as I like the manual control. Whether you are using a manual or an auto-ranging DMM, you should have an idea of roughly what kind of voltage you expect to find at a particular point before poking the test prods anywhere near it. Knowing what voltage (or current, or resistance) ball-park you are in, it is no trouble, in my opinion, to switch the meter to the appropriate range. That may be just be my justification for the fact that I’m rather stuck in my ways, and just happen to prefer manual meters. It’s convenient that they are cheaper too🙂 With a DMM like this as your sole piece of test gear, you can build an awful lot of stuff. There are cheaper DMM’s out there, but the really cheap ones have low build quality and poor accuracy, in my experience. I do also have an old Tek 465 oscilloscope which a local ham very generously gave me. Combined with a signal generator, you can do all sorts of fun things with a ‘scope, such as injecting a signal into an amp stage, and seeing what it looks like when it comes out (as well as calculating the gain of the stage). I recently used it to measure the output of a 5mW QRPp transmitter, by measuring the peak to peak voltage across a 50 ohm resistor. At such low output powers, RF probes aren’t accurate, and a ‘scope is a good way to go.

My DMM doesn’t measure capacitance, so this capacitance meter does a great job. I often check values of components before installing them into a circuit, as a double-check to ensure I didn’t misread the value printed on the part. I got this one for a little under $15 from Sparkfun. It measures capacitances from just a few pF up to many uF’s –

There are some really useful cheap pieces of test gear on eBay. I plan to ask for a little frequency counter, and maybe also an ESR meter for Christmas.

Anyway, the purpose of this post was to show you the tools I use for my home-brewing activities and hopefully, to demonstrate that you don’t need a lot of expensive ones to build a lot of cool things. However, if you have the interest and can afford it, feel free to get yourself lots of cool test gear!

Those are the basics, I think. I cannot think of any more right now. If you have any questions, feel free to ask them in the comments section and I’ll do my best to answer.

October 21, 2015

How Do Lacquered Boards Stand Up Over Time?

A query I hear from time to time about using copper-plated boards for Manhattan construction is what they look like after a few months or years. “How do they age?” is the question. My first such project, the WBR, was housed in an enclosure made from double-sided PCB material, and I could see that the outer surface had developed a bit of oxidation; a certain patina, if you will. My later projects weren’t made from this double-sided PCB – just single-sided, so I was going to have to open them up to see how they’d fared. Comparing how they looked, and remembering how I’d applied the lacquer to each did help in coming to some conclusions.

First of all, this is how the outside of the WBR looked shortly after I finished building it just over 4 years ago. It was already showing a few early signs of oxidation. However, it did fit together very well, and made quite a handsome enclosure –

The WBR in July 2011

I made 2 mistakes with this enclosure. Firstly, although the initial cleaning of the boards was done with Scotch-Brite scouring pads, the final cleaning was with Tarn-X. I later found that copper boards cleaned with Tarn-X develop streaking and oxidation. The streaking on this WBR enclosure was not anywhere as near as bad as I have seen with other boards, but it is definitely there. You can see it on the side panel in the next shot. The other mistake was to spray the lacquer too lightly. I was cautious about spraying it too thickly and causing it too pool, so I erred in the other direction instead. This is what it looks like from the outside today. Not bad, but definitely aged. You can see the areas on top where my fingers press against the case when I pick it up –

The WBR today (Oct 2015)

Here are a few more.

Before (July 2011) –

The WBR today (Oct 2015)

and today (Oct 2015)  –

The WBR today (Oct 2015)

The WBR today (Oct 2015)

If I were making the WBR again today, I’d stay away from the Tarn-X, and apply slightly thicker coats of lacquer.

Next, I decided to open up The Rugster. It was a little direct conversion receiver I had made by teaming up a standard NE602-type DC receiver front end with NM0S’ Hi-Per-Mite filter, set for maximum gain, so as to provide both 50dB of gain and narrow filtering. I built it into an enclosure made of single-sided copper-clad board on a red laminate. It had a really cool and compact look –

The Rugster in July 2012

It still looks the same from the outside today, but I was curious to know what the interior looked like. This was what it looked like when freshly-built 3 years ago, in Aug 2012. The treatment of the VFO toroid was my first ever attempt at using a hot glue gun, by the way. I am more skilled at it now. This particular toroid looked a bit of a mess –

The Rugster today (Oct 2015)

The same view today (Oct 2015), looking remarkably good. You can see that I added a high-pass filter on the back panel set to block signals from the AM broadcast band –

The Rugster today (Oct 2015)

I do remember that I sprayed slightly thicker coats of lacquer than on the WBR, leaving each coat for about an hour before spraying the next coat. Here are some more “after” shots –

The Rugster today (Oct 2015)

In the next one, the brighter patch on the red front panel is a splash of morning sun, and not a discoloration of the laminate –

The Rugster today (Oct 2015)

The 3rd project to be given a second look was the VK3YE Micro 40 DSB transceiver, which I built 2 years ago, in Oct 2013. Back then, the innards looked like this –

The VK3YE Micro 40 DSB Transceiver in Oct 2013

A couple of days ago (Oct 2015), it looked like this –

The VK3YE Micro 40 DSB Transceiver today (Oct 2015)

The VK3YE Micro 40 DSB Transceiver today (Oct 2015)

I used to clean my boards with Scotch-Brite pads but now find that fine steel wool scouring pads work even better. Then, when they’re clean, I dry them with clean bathroom tissue, making sure to blow any loose fibers off afterwards. Then I spray the first coat of lacquer. To this day, I still don’t always judge it correctly, and end up with boards that don’t age too well, but IMO, it is best to spray until it is just beginning to pool, ever so slightly. At this point, the lacquer is quite thick, but will smooth out before it dries. An hour later, you can spray the second coat. I’ll leave it up to your judgement as to whether you apply a 3rd coat (I usually do). From my experience, this way works quite well. I’ll be interested to hear details of anyone else’s experience with lacquering.

In the next post, I’ll talk a little about the methods I use when constructing Manhattan boards.

October 6, 2015

Some More Sproutie MK II Videos

Since finishing The Sproutie MK II and publishing the blog-post on it a few weeks ago, I have been listening to it, winding an extra coil or two, and also attempting to tweak the active audio filters. Coverage of The Sproutie is now up to 18.3MHz, and while I know from previous experience that it will cover up to 30MHz, I am going to leave the upper limit where it is for the time being. Any new coils will most likely be wound for more limited coverage on specific bands under 18MHz. PS – I just spent part of the morning testing out the upper limit of the newest coil by listening to SSB on 17M, and it’s working great – quite stable too.

I had wanted to give the CW and SSB active audio filters more gain, to compensate for the fact that in those modes, the RF gain needs to be wound down to prevent oscillator pulling. Because the narrower filters, even if they have the same gain as the wider filters, give the perception of lower volume, I wanted to design them with higher gain to compensate. Currently, the narrowest filter, a 700Hz low-pass, has a gain of 20dB. I tried building 700Hz low-pass filters with gains of 46 and 34dB, but they both oscillated, putting out a square wave with 10V amplitude at a frequency of somewhere in the region of 100-150Hz. I made sure to keep the Q below 3 – in fact the highest Q stage in the 34dB filter was just a little over 2, but this didn’t help any. For the time being at least, I have decided to keep the current filters as they are. If you view the videos, you’ll see that The Sproutie does indeed work on SSB and CW. If receiving a weaker station for which the set could use a little more gain, plugging headphones in helps and at this point, it’s a compromise I’m willing to make. Trying to build the perfect regen is a rabbit hole from which it sometimes feels as if there’s no escape, so I decided to draw a line in the sand and leave things as they are.

Once again, I feel as if I should apologize for the quality and resolution of these videos. I just entered the 21st century a few months ago with the acquisition of my first smartphone, a first generation Moto G. It’s a budget model, so doesn’t have the best video. It is an improvement on the videos I used to post from my decidedly old Canon Powershot A80 though. The one thing the videos do achieve, I think , is to give you some kind of feel for what the receiver is like to operate. For detailed views, the still photos are the way to go.

This one shows how a regen, if you nudge it into gentle oscillation, can provide some carrier injection for reception of weak AM stations –

Here’s the 25M SW broadcast band –

And another video on the 40M amateur band on CW and SSB, with a special brief guest appearance by Jingles the blind kitty –

September 14, 2015

The Sproutie MK II HF Regen Receiver

NoteIf you have read this article before and are checking back in, it would be a good idea to clear your cache, to ensure that you are viewing the very latest version of this post. I do add material and make corrections from time to time.

It’s been about a year since I finished building The Sproutie, and it’s been a good year. Of all my scratch-built projects, it has been the most satisfying to own. It works well, looks pretty good and also, there is always the lure of possible of tweaks and improvements. This is partially because it’s a home-brew project, and also because it’s a regen🙂 It was really enjoyable to build a receiver with the basic circuit architecture taken from the 1930’s, but with a combination of solid state devices and lovely old vintage parts.

I have continued to occasionally purchase vintage reduction drives and variable capacitors. After using a National N Dial for the main tuning control in The Sproutie, I became quite pre-occupied with what, to me, is close to the ultimate dial and drive for an analog receiver – the classic National HRO micrometer-type dial and gear drive. I wanted to find a good example of one of these, and use it in a regen.  I also spent quite a bit of time performing Google searches using phrases such as “best regen receiver ever”, and “the ultimate regen”. These are the kinds of things I search for when at a loose end, in the vague hope that I’ll magically find the most amazing regenerative receiver ever designed and built! One very inspirational regen I did discover while searching for the “ultimate regen”, was Jim K4XAF’s build of Bruce NR5Q’s “Ultimate Regen”. What a beautiful receiver! It’s a tube set, built on 2 separate chassis. One chassis contains the main receiver, while the other houses the power supply, the speaker, and the “Selecto-O-Jet” audio filtering. It makes use of a National HRO dial and gear drive for the main tuning, along with National “Velvet Vernier” drives to control the regeneration and variable antenna coupling. Now this was the type of regen that inspires true longing, and convinced me that as enjoyable as The Sproutie was to build and own, I needed to build just one more regen🙂

Initially, I was hoping to use a different type of circuit for this receiver from the tried-and-tested front end used in The Sproutie. I did build VE7BPO’s regen #4 and had some trouble with it picking up a local FM broadcast station. In retrospect, I should have realized that I have had this issue with other simple receivers at this location, until they were cased up and grounded properly. The problem seemed to be a little worse than normal, but this could well have been due to the amplification factor of Professor Vasily Ivanenko’s hycas detector. I gave up far too soon and headed for the security of the front end I used in both the first version of my Sproutie, and the WBR. It is, of course, the circuit used in Nicky’s TRF, as featured in issue 70 of SPRAT (with a few corrections and suggested mods in issue 72). Incidentally, “Bear” NH7SR built a very functional version of Prof V’s Regen #4 which he described in this thread over on The Radio Board.

However, I didn’t just want to exactly duplicate the circuit of The Sproutie, even if the new receiver was going to have a different physical form and different hardware. This new receiver would have to have some alternate type of circuitry that would make it worth building. I was interested in trying a different type of filtering in the audio chain, and a tip from Prof V in his Solid State Regenerative Receivers group on Google+ clued me in to a great tool for designing active audio filters (more on that later). The pieces were beginning to come together. I had a bunch of NE5532’s in my parts stash that had sat unused for a couple of years and it struck me that a regen which utilized a series of active audio filters for different bandwidths, switched from the front panel, might be an interesting idea for a receiver. The LM380 output stage I had used in The Sproutie works well, so I saw no reason to change it. It is fairly low noise, a welcome factor that makes it possible to listen to a receiver comfortably for long periods of time.

Here’s the block diagram of The Sproutie MK II. As it contains 6 separate AF filters, I decided to also switch the +ve supply to the filter. A 5532 active filter draws about 7mA (14mA if using 2 x op-amp stages). Although it’s not a lot of current, it’s a fairly significant amount relative to the total consumption of this receiver if all 6 filters are continuously powered. One of the reasons I prefer solid state over tubes is the power efficiency, so no reason to keep all 6 filters powered if only one is being used at a time –

Fig 1 – Block diagram of The Sproutie MKII. Note that S1a, S1b and S1c are all part of the same rotary switch.

The front end, as I mentioned, is exactly the same one I used in the original Sproutie. It is the one used in Nicky’s TRF featured in issue 70 of SPRAT. I thoroughly recommend joining G-QRP. Your initial membership includes an archival DVD of past issues of the club magazine SPRAT, which is a very valuable resource for homebrewers. If you have access to this archive, you should also take a look at issue 105, in which a slightly different version of the same receiver is featured. It employs a simple passive LC audio filter, if you’re not keen on the extra complexity that my version here entails.

Here’s the schematic of the front end. The oscillator tank circuit has been simplified to just one variable capacitor, and all details of the plug-in coils removed, purely for the purposes of making the circuit a bit easier to understand. If I drew the octal coil socket without the coil (as I did with the schematic for The Sproutie) it would make the process of understanding the circuit diagram a bit less intuitive –

Fig 2 – The Sproutie MKII front end, with details of plug-in coils and fine tuning capacitor removed for simplicity.

Here are details of the coil base, using an octal tube socket. You can use any pin configuration you like – this is the one that worked for me. It is the same configuration as used in The Sproutie –

Fig 3 – Plug-in coil base wiring

The final AF amp is a simple LM380 circuit. It’s easy to build, is fairly low-noise, and it works. If you’re used to AF circuits which use an lm386 in high-gain mode, with a 10uF cap between pins 1 and 8, you are going to love the much lower-noise performance of this circuit! As well as a phone jack, I included a jack for an external speaker on the rear panel. It took me a while to figure out how to wire the internal speaker and the 2 jacks properly.  I wanted the internal speaker to cut out if either headphones or an external speaker were plugged in. I also wanted the the external speaker to cut out if the headphones were plugged in. It’s a simple problem really, but simple things often elude me. I got there in the end –

Fig 4 – The AF output stage. The “bass” switch only gives a very gentle lift to the lower frequencies. The effect is so subtle that you won’t be missing much if you leave it out.

The thing that makes this receiver different from the original Sproutie, electrically speaking, is the bank of switched active audio filters. If you don’t want to be bothered with building multiple filters, and switching them all with a switch, you could permanently wire just one filter into the circuit. Another idea would be to replace this bank of switched filters with an adjustable filter made from op-amps, with the center frequency and bandwidth controlled by potentiometers on the front panel. Once you bring op-amps into the mix, all sorts of things are possible. Another idea suggested by Bear NH7SR, is a 5KHz audio notch filter, which could be quite useful for AM SWBC listening. The design tool that made all this happen for me was by Texas Instruments (thanks Prof V). There is an online version called Webench Filter Designer. It has a user-friendly interface that actually made the process of filter design harder for me than the offline software they also offer, called Filter Pro. Use which one works best for you – they are both accessible from this page (opens in a new browser window). Of the two, I recommend Filter Pro. You can use this software to design low-pass, high-pass, bandwidth, allpass (time delay) and notch filters. I stuck with low-pass filters. I was tempted to try a bandpass design for the CW filter, and may still do at some point. The CW filter I constructed was the very last filter out of 6. By that time, I didn’t have the patience for the slightly more complex design of the bandpass filter. I also rationalized that I might need to tune through a CW signal to hear the other side of it, if trying to escape QRM, so a lowpass would make this easier, as I’d be able to hear the signal all the way through to zero-beat and out the other side. This might simply have been my excuse for not wanting to build a bandpass filter🙂

I wanted a “straight-through” position to give me something to compare the other filters to. All the filters, with the exception of the narrow CW filter, were designed with a 6dB gain, so I designed my “straight-thru” filter with a 6dB gain also, so I could step through the bandwidths seamlessly. If doing this again, I would have given the filters a bit more gain. I’ll explain why later. Dan N7VE gave a talk to the Arizona QRP Scorpions a few years ago on (among other things) designing active audio filters. It’s definitely worth taking a look at his presentation, which is available here. In fact, I wish I’d paid attention to it before embarking on designing the filters for this receiver, as I would have tweaked some of the resistor and capacitor values a bit. Dan explains how it’s desirable to keep the resistors in the main signal chain fairly low in value, to avoid noise. He recommends trying to stay under 1K. I only read the presentation before designing the very final filter – the CW one with a cut-off of 700Hz – so while my resistor values in that filter are nice and low, they are not quite so low in the others (though in my defense, they are not atrociously high either).

Here’s the first, and widest filter. As far the ear is concerned, it’s not really a filter, as it has a cut-off set at 20KHz, with a gain of 6dB –

Fig 5 – The “straight-through” filter (an LPF with a cut-off of ~20KHz)

I wasn’t interested in the shape of the response as, for this stage, all I wanted was effectively an unfiltered stage with a gain of 6dB. For this reason, I used just one half of a dual op-amp 5532 package as a real-pole filter. Filter Pro doesn’t show the power supply and biasing arrangements, so I added the 2 x 47K resistors to keep the input biased at about half of the supply voltage. I also added the 10uF capacitor, which keeps the bottom end of the 1K resistor at ground potential for audio signals, while blocking the DC bias. I also added the lowpass filter formed by the 10 ohm resistor and the 100uF electrolytic on the supply line, as well as the 0.1uF ceramic RF bypass cap on pin 8 of the IC (mounted close to the pin). I don’t know how essential these 0.1uF caps are, but the datasheet suggests them, and they can’t do any harm.

The other filters were all 4th order low-pass filters (2 stages = 1 x 5532 dual op-amp package), with the exception of the 2.4KHz filter, which was an 8th order low-pass filter (4 stages = 2 x 5532 dual op-amp packages). The 8th order filter has a sharper cut-off, of course. Feel free to design your own filters, with the help of Filter Pro, for whatever cut-off frequency and rate of roll-off you wish. I’ll show you the R and C values I used for my filters but you might want to fiddle around with the software and come up with your own values that keep the R values in the main signal chain at or below 1K, if possible. The resistors in the first stage of the filter are particularly important, as the noise they produce is amplified more than noise produced in later stages. Just click on a component in Filter Pro, enter a different value, and hit return to see what new values of the other components the software has calculated. A bit of trial and error should get you close. Also note that you can specify the series of resistor and capacitor values you want to use (E96, E48, E12 etc), and watch how the filter response curve changes as you change the tolerances and values.

First of all, here’s the gentler roll-off 4th order filter that uses just one 5532 8-pin dual op-amp IC – or use the op-amp of your choice. I chose the 5532 because I had a bunch of them in my parts stash and because they are the 2N2222 of the op-amp world – plentiful, reasonably priced, and all over the place –

Fig 6 – Schematic for the gentler roll-off 2-stage LPF

Here are the component values I used for my 4th order filters –

Fig 7 – Component values for the 2-stage filters in my Sproutie MK II

For a sharper roll-off, an 8th order filter, which uses 2 x 5532 dual op-amp packages (or equivalent) –

Fig 7 – Schematic for the 4-stage sharper roll-off LPF

The 2.4KHz 8th order filter I used, although a bit on the narrow side for SSB, is good for listening when there are nearby stations higher in pitch that need cutting out. If you think about it, this 2.4KHz LPF is going to sound roughly like the 2.1KHz filter in a regular SSB rig. The reason for this is that your regular SSB filter is a bandpass filter, with the bottom edge being set to cut off at about 300Hz. This means that a 2.1KHz SSB bandpass filter will pass frequencies up to about 2.4KHz (2.1KHz + 300Hz). Here are the values I used in mine –

Fig 8 – Component values for the 4-stage filter

After I had built the receiver and all these filters, and done some listening, I concluded that for SSB and CW, a bit more filter gain would be helpful. The set has plenty of gain when listening to AM but on CW/SSB, the RF gain has to be wound right down to prevent the oscillator pulling. This creates a need for more AF gain in the CW/SSB modes. At the time of writing this, I have only just finished building this set and have no enthusiasm for building more filters. I actually had to build 8 filter boards to get the 6 that I used, and 3 front end boards to arrive at the final one. Together with the physical side of the construction, I am tapped out right now and have no desire to construct anything else at all for a while!

If you want to use this receiver mainly for SSB and/or CW, you may want to experiment with the value of the NPO capacitor in the front end that connects the hot end of the main tuning coil to the base of the 2N3904 oscillator transistor. It is listed on the schematic as being 39pF, and that is the value I used. However, it is possible that a lower value will cause the oscillator to pull less on strong signals. Of course, the lower value might also reduce the signal strength into the detector which will put you back to square one. It’s worth trying though. I’d be tempted to try a value as low as just a few pF. Remember that changing this capacitor will affect the frequency coverage – particularly at the top end of each range.

When building the filters, I originally built the 700Hz CW filter with a gain of 6dB, like the other filters. The idea is that if they all have the same gain within their passband, the operator can step through the different bandwidths without a change in the volume of the wanted signal in the speaker. This was the way it worked except with the 2 narrowest filters. The 2.4KHz 4 stage filter had a slight, but noticeable drop-off in volume. The effect was very pronounced with the 700Hz filter – so much so that I redesigned it with a gain of 20dB and still found that there was a slight drop-off in volume within the passband as compared to the other filters. I don’t know the reason for this. EDIT – Thomas LA3PNA Tweeted the following explanation – “The perceived loss when changing filters is because the power delivered to your ear is 10log(BW of filter) and less with less BW. So basically, the reduction in noise makes it sound like the volume goes down”  He also gave a very useful tip for adjusting the gain of the filters so as to preserve the perception of constant volume – “I like to add gain in a filter circuit after the formula 20log(bw/orginal bw) for AF filters”  That is very useful information Thomas. I’m a little tapped out after building The Sproutie, but if and when I decide to revamp the filter bank, I’ll be paying attention to this formula.

I may, at some point, rebuild the 3 narrowest filters with higher gains. If that ever happens, I’ll report the results here in this post. Incidentally, at this point, allow me to say one more thing about the filters. If building and wiring up all these filters sounds like it is making the construction of a regen overly-complicated, I can definitely sympathize. If you want to use this set for CW, SSB and AM and you want to permanently wire in just one filter, I’d go for a 4th order (2-stage) LPF with a cut-off of 3KHz. The one I have is perhaps a touch wide for SSB (it’s roughly equivalent to a 3.3KHz passband filter, as explained earlier) and a bit narrow for AM broadcast, but it’s a good compromise for both. If it were the only filter I had, I know I would get used to the sound of it. As for the gain, mine has a gain of just 6dB, but I’d like to up it in order to have a good volume when turning the RF right down, as is necessary to prevent oscillator pulling on SSB/CW. I can’t know until I’ve tried it, but I’m thinking something along the lines of 26dB gain. Just make sure to be careful when on AM, as you may find that you have way more gain than you need – so keep an eye (and a hand) on that RF gain control.

A big part of the inspiration for building this receiver, as I mentioned earlier, was the physical form of K4XAF’s version of NR5Q’s Ultimate Regen. In the search for a National HRO dial and gear drive in really nice condition, I bought several, and finally came up with a dial and drive combination that just cried out to be included in this receiver. This gear drive has a shaft rotation limiter, which was perfect, as the tuning capacitor I wanted to use didn’t have any kind of rotation limiting built in – it was the capacitor in the first photo in this post – a Hammarlund MCD-50-M. The final M stands for midline, referring to the fact that the off-center shaft and shape of the vanes help to make the tuning a lot more linear than with regular variable capacitors. With a standard capacitor, you’d find that the frequencies would become very compressed at the top of the tuning range i.e. the tuning would get a lot more fiddly. Try to get a midline unit. I believe they also go by other names, depending on the manufacturer.

Of course, a big dial and gear drive need a big chassis, and Terry from Seaside Chassis, who made the chassis for The Sproutie, came to the rescue again. I decided to use a chassis and front panel that would be compatible with 19″ rack cabinets, for a variety of good enclosure options. A chassis that big needs to be fairly thick in order to still be stout and solid. Terry does offer the use of 12 gauge aluminum for bigger enclosures, and I wanted this receiver to be big and solid (although compared to your average boat anchor, it’s still relatively light). As well as a large, stout chassis, I decided that I wanted to try designing a custom front panel with the services of Front Panel Express in Seattle using their free design software. Right at the beginning of this whole project, in the first month or two of 2015, I downloaded their software and casually laid out a very rough front panel, mainly for the practice, and the fun of learning something new. As the project progressed, I’d spend a few weeks working on circuit boards, then go back to the front panel, then do a bit of work on the plans for the chassis, to send to Terry. I had an idea that, with a bit of luck, I’d complete the whole thing in or around the fall, and that’s how it worked out. At no point did I rush though. Why rush? Besides, the longer a project takes, the less it costs per month. I could see that building this regen in the way I had chosen to build it was not going to be a cheap affair, so I took my sweet time.

Here is the chassis as it arrived from Seaside Chassis, along with 2 side braces for supporting the front panel, 2 mounting brackets for the main tuning capacitor, and 2 mounting brackets for the regeneration pot. I only needed 1 of each of these brackets, but like to have extras on hand. As it turned out, an extra bracket was needed to help secure the main tuning capacitor which I forgot to ask Terry for, so I put in an extra order. The shipping from Canada dwarfed the cost of the bracket but at this point, it was easier to ask him for it than to find someone local and besides – I just wanted him to fabricate all the chassis components. Terry’s work is first-rate. It’s good to give him as much relevant information as you can. Simple drawings with penciled-in dimensions work well. If it’s important to you, remember to take into account the thickness of the aluminum if there are any dimensions that are particularly critical. Also remember that he is bending and fabricating these components by hand, so allow for a certain amount of tolerance in the final dimensions. Having said that, the chassis he supplied was remarkably close to the exact dimensions I requested, and within the tolerances I had allowed for. If you have any dimensions that are particularly critical or non-critical, I think this is all good information to pass onto him when making your request –

Figuring out exactly where to drill holes for controls in front panels and enclosures usually takes quite a lot of time. It’s a bit like a game of chess in that every decision you make affects everything else down the road. To make matters tougher, I have trouble thinking about more than one thing at a time, so juggling all the variables in my head takes a lot of thinking, measuring, and drawing. For front panels, I always draw the shape of the panel on a full-size sheet of paper, and place all the knobs and controls on it to see how they look in various configurations. Just when I think I have it right, I leave it and walk away, often overnight. On returning, I inevitably come up with an improvement or two. Building something like this is all baby steps for me. I am impressed and amazed by builders who claim to be able to throw something like this together in a few afternoons – this one took me over 6 months. Heaven knows how long a more complex receiver, such as a multiband superhet, would take me.

I took a great deal of time and care in designing the front panel. They are worth every penny, but they are not cheap. I didn’t want to make a mistake that would result in having to re-order the whole thing. So after checking, rechecking, going to sleep, then waking up and rechecking again, I went through this whole process several more times before finally clicking “order”. A week or so later, this beautiful 4mm thick aluminum panel arrived via UPS, packed with a little bag of gummie bears –

Gummy bears!

The front panel as it arrived from Front Panel Express, vacuum packed to a stiff baseboard. The metal ruler is 18″ long (the panel is 19″ wide).

Look at this beautiful, black anodized front panel!

I just couldn’t get enough of this thing when I first saw it –

There were some scratches in the black finish on the rear, but this is normal. I later found out that  it is possible to add a note when ordering, to ask the people working with the milling machinery to take extra care with the back side of the panel. The front surface is guaranteed, but not the back.  I decided I was OK with the rear of my panel as, well, it was the rear, and the bottom half of it would be in direct contact with the front of the chassis anyway –

You’ll notice a number of “blind” holes milled on both the front and rear. The panel is so thick (4mm) that controls sticking through both the chassis and this panel wouldn’t protrude far enough for the nuts to thread onto the bushings. For the RF gain, AF gain and filter rotary switch, the blind hole was milled on the front side, as the knob would cover it. For the phone jack and bass switch, the blind holes were milled on the rear. Here’s a close-up of the blind hole on the rear side for the bass toggle switch. You’ve probably figured (if you didn’t already know) that a “blind” hole is one that doesn’t go all the way through the panel –

After the initial euphoria of receiving this fantastic front panel had subsided a little, it was time to put some time and labor into making all the remaining cut-outs in the chassis. I had asked Terry to make the holes for the octal tube socket and the main controls, but there were others that still needed to be done. My usual method of making non-standard cut-outs and holes is very time and labor-intensive, but it works quite well. I mark the edges of the cutout with a pen or pencil, then with a hand-drill, drill lots of small holes around the perimeter. Then, with an old screwdriver, I knock out the piece of metal in the center, and clean up the edges with files, usually using a bastard file first, and finishing off with something finer. These photos should help illustrate the process. The speaker cut-out was inspired by a WW2-era British military R107 receiver that I owned as a teenager. It is simple – just 4 large holes arranged in a square. This is the “during” photo, showing the series of small holes drilled around the edges of the holes. The rectangular cut-outs to the right were made using the same technique, incidentally –

– and after –

Here’s another photo, taken a bit later during the assembly, showing the placement of some of the main components. This particular National HRO NPW gear drive, unlike most that I have seen, has a shaft rotation limiter. The tuning shaft is a little on the short side. I needed to mount the gear box as close to the front panel as possible in order to be able to mount the dial properly. If you scroll back and look at the photos of the front panel, you’ll see there are 3 smaller holes located around the main hole for the gear drive. These holes helped in locating the gear box as close to the front panel as possible (the 3 screw heads fit into the 3 smaller holes on the front panel). Most of these gear boxes don’t have this rotation limiter, so the extra holes won’t be necessary. Also, do you see the aluminum shaft couplers on the regen pot and fine tuning capacitor? Those are quality parts personally machined by John Farnsworth KW2N. The one on the right is a standard 1/4″ to 1/4″ coupler, while the one on the left was made to order. It couples the 1/4″ shaft of the 10-turn regeneration pot to a short 3/16″ shaft that the National knob fits onto. I wanted to use the same type of National Velvet Vernier knob and escutcheon plate for the regeneration that I used for the fine tuning, but I didn’t want to use the 5:1 reduction drive. I wanted to use a 10-turn wirewound pot instead, as I like the feel of those pots. From the front (as you will see in later photos) the 2 National knobs and escutcheon plates look the same. However, the knob on the left is connected directly to the 10-turn pot and not to a National Velvet Vernier reduction drive. The black escutcheon plate for the regen control is spaced away from the front panel by one washer thickness, and bolted to the front panel with 4-40 hardware. It is not used for anything, other than looks.

Now, let’s look at some of the boards. They were built, as always, with W1REX’s very useful MeSQUARES and MePADS. This is the AF output stage and the 4KHz filter mounted on one board, and installed in the chassis. The idea was that this board, together with the main RF board, would form a working receiver, after which I could build and install the other filters, one by one –

Mounted above the AF output stage, on the stand-offs, is this next filter board, carrying 2 LPF’s. The first filter to be built was the 6KHz one –

Next came the 3KHz filter (in the foreground of the next shot). The grey rectangular poly capacitors were from Tayda Electronics. Thier prices are low, and the caps seem good. The resistors are 2 types – either 5% carbon film from the parts stash I had as a kid in England in the early 80’s. They lasted a long time, but I am beginning to run out of them. The others are newly-acquired Xicon 1% metal film parts, purchased in lots of 200 from Mouser –

The same board, taken from above (3KHz filter on the left, 6KHz filter on the right) –

The same board, with the 3KHz and 6KHz filters, mounted in the chassis above the 4KHz filter and AF output stage –

Here are 2 shots of the 4-stage (8th order) 2.4KHz LPF, with temporary leads in place for testing. It’s quite the QRM-buster –

At this point, allow me to introduce the main RF board. Electrically, it is exactly the same as the one in the original Sproutie. I tried a couple of small mods but went back to the original. So – nothing new here, except for a small physical detail that I learned from my experience with The Sproutie. There are 2 pads on the board that connect to the octal tube socket with (ideally) short, stiff wires. In the original Sproutie, I used very short lengths of solid 16 gauge wire. They were so stiff that, over time, with repeated insertions of coils, the wires placed enough stress on the pads to detach them from the board. It took me a while to figure out why the dial calibration was suddenly off by about 10KHz. The pads had only separated from the board by 1mm at most, so it was hard to see, but it was enough to throw off the dial calibration, and cause it to change slightly in an unpredictable fashion. I did 2 things to remedy this. The first was to replace these 2 wires with thick stranded wire, which I tinned thoroughly. The tinning stiffened the wire, but it still had more flex than the original solid 16 gauge wires. Secondly, I removed the 2 pads, and re-attached them with epoxy instead of superglue. Problem solved!  When I built the Sproutie MK II board, I attached these 2 pads with epoxy (I used JB Weld). Superglue gel was used with all the other pads, as before. The 2 pads in question are at the very front edge of the board in the next shot. They are the second and third pads from the right. Missing from this shot is the 0.1uF capacitor that couples the audio to the next stage. There is also one extra capacitor that was part of a mod I later uninstalled. I’m showing you these shots to give you the overall idea of layout, what it looks like, and because it’s fun looking at circuit boards. For absolute accuracy of the circuit, follow the schematic –

The next 2 shots are the same board, but at an earlier point when I was using 1uF caps for interstage coupling. They are the 2 blue box-like caps. They didn’t make it to the final version of the board –

Here’s a wider view of the underside of the chassis at this stage of the construction, showing the main RF board wired to the octal tube socket, as well as the AF output stage with 4KHz filter, the 3KHz and 6KHz filter board on top of it, and the 2.4KHz filter board sitting on it’s own for the time being –

A closer view from a slightly different angle. At this point, it was beginning to dawn on me that keeping all this wiring tidy would take a bit more work than I had anticipated. I never did get the wiring as tidy as I wanted, but it’ll do –

This one’s a bit boring. It’s the “straight-through” real-pole LPF with a cut-off frequency of 20KHz, shown installed in the chassis on top of the 2.4KHz LPF –

and the 700Hz CW low-pass filter –

Here are all those filter boards stacked on top of each other. Looking at the left-hand stack first, from the top down is the 700Hz filter, the 20KHz “straight-through” filter and, at the bottom, the 2.4KHz sharp roll-off filter. On the right-hand side is the 3KHz and 6KHz filter board, with the 4KHz filter and AF output stage board on the bottom. You can also see the 6-position rotary switch that selects between the different filters. I had no trouble finding a 6-position switch with 2 poles but when I decided to also switch the +ve supply line to the filters, finding one with more than 2 poles proved tricky. I finally found it from a supplier of parts for musical instruments. It is distributed by AllParts, and is part number EP-0920-000. It is a 6-position 4-pole switch (one pole goes unused). Prices vary a bit, so search around for the best deal if you want this particular switch. If you want fewer filters, then you’ll probably find it easier to locate a switch that has 3 or 4 poles and 4 positions or less. This is the finished receiver, by the way. Well, finished for the time being – until I decide I just have to modify something –

Some more views of the underside of the finished receiver. You’ll notice that I designed a rear panel too. That also came from Front Panel Express – a more detailed view of it is coming later. The speaker is an 8 ohm, 4 inch, 6 watt unit made by CUI, model # GF1004. I got it from Digi-Key, part # GF1004-ND. Before finding this speaker, I purchased one from a company well-known for supplying vintage radio parts. It turned out to be very lightweight, with a small magnet, and generally rather disappointing. I liked the speaker I used in The Sproutie, so got the 4″ version of that one instead (the one in my Sproutie is a 3″ version). The aluminum speaker grille was custom cut by speakerworks.com

Coils were constructed in the same fashion as the coils for The Sproutie. In fact, the pinouts used on the octal socket are the same, so my Sproutie coils work in the Sproutie MK II, though they cover a wider range, due to the greater maximum capacitance of the tuning capacitor I used – a 2 x 50pF instead of the 2 x 35pF used in the original Sproutie. I decided to wind a complete set of new coils for this receiver. As of writing this post, I have 6 coils wound with a few more to go, as needs and desires dictate.

With The Sproutie, I used nylon hardware to secure the larger T68-6 toroids for the lower frequency bands. On the higher frequency bands, I used T50-7 toroids, and secured them with hot glue. This time around, I found that hot glue worked perfectly well for securing the T68-6 toroid cores too, so I used that technique exclusively. It’s faster and easier than using nylon nuts, washers and bolts. I didn’t think it would be the case, but if you need to re-make a coil, you can peel/break the glue off and re-use a tube base. In fact both the coils in the photos below were made with bases that were used at least once before –

I like these ceramic bases, because they are just a little higher than the phenolic ones, offering a bit more protection to the toroid. Wherever you get yours from, if they’re ceramic, they may well be the same ones as these, as most of these bases and sockets seem to be made in China these days –

“Take us to your leader”

You’ll need to figure out the exact details of your coils with the help of online calculators (I like the ones on W8DIZ’ site) and good old trial and error, but here are my details – they should give you a start. Remember to take into account the values of main and fine tuning capacitors, if they are different from mine – and the value of that 39pF capacitor between the tank and the base of the oscillator transistor, if you try a different value. I’ll update this table as I wind more coils. The plan is to wind general coverage coils up to about 21MHz or so, and a few more coils for specific bands. It is much easier, with the aid of the dial calibration graphs, to pinpoint exactly which 5KHz channel you are on, when the band coverage is limited to 1MHz or less. With the 20:1 reduction ratio of this National HRO drive, and the large, relatively massive dial, I found it quite easy to tune in stations even on the 13500-18300KHz coil, which spans almost 5MHz. For pinpointing which 5KHz “channel” I am on though, a general coverage receiver to listen to the oscillator of The Sproutie is more reliable (and faster) than reading dial calibration graphs.

For dial calibration, I use a piece of freeware called Graph. You won’t be able to read the following graph, as it’s a bit small. The original is a bit larger, and the software has an option for zooming in on a particular area of the graph. This is the dial calibration graph (so far) for my 5475-8450KHz coil –

I guess it’s time to do a reveal and show you what this little feller looks like from the front. You wouldn’t think it, but I spent a great deal of time on the front panel, figuring out the exact placement of all controls, placement of the lettering, and fonts. I was looking for a specific type of vintage knob for the RF gain, filter, and AF gain controls, but didn’t find any in good condition while building the receiver. Then I found some knobs on clearance at my local Radio Shack. Those are brand new RS knobs, but I think they look good and fit in well with everything else on the front panel. My main concern was to not “overdo it”. When sitting at the computer with the Front Panel Designer software running, it’s quite tempting to go overboard on the lettering, or try a colored panel, and colored letters in a fancy font. Just because you can do something though, doesn’t mean you should, and I wanted a front panel that was understated, functional, and that would still look good, regardless of how my personal aesthetic might change. Minimalism is the key, though the one extravagance I did allow myself was the larger “Sproutie MK II” declaration, and my callsign. I did try my callsign in red but decided that it looked gaudy. Best to play it safe, I think. I was also concerned that the finish might be a bit too shiny or glossy, but it turned out to be matt with a slight sheen. I’m very happy with how this looks –

Although the regen and fine tuning knobs, and escutcheon plates look the same, the ones on the right are attached to a National “Velvet Vernier” 5:1 reduction drive, via a fairly long coupling shaft. The knob on the left is connected to the 10-turn regen pot (via a 3/16″ to 1/4″ shaft coupler), while the black escutcheon plate is spaced away from the front panel by washers, and attached to it in a fixed position with 4-40 hardware –

Here’s The Sproutie MK II with her little sister, for size comparison –

A quick word about that regen control. On first installing the main RF board, one filter, and the AF amp into the chassis, I noticed that occasionally, when receiving a strong carrier, I’d hear a ringing in the speaker. My first thought was that it was microphonics caused by physical feedback between the internal speaker, which was bolted to the chassis, and some part of the circuit. Plugging in headphones didn’t cause it to go away, however. Undeterred, I continued building, and it was only after finishing the whole receiver, that I realized what was going on. I discovered that if I hear a ringing, all I have to do it back off the regeneration control a bit, and it disappears. I think this ringing is due to the high Q of the circuit when set right at the threshold of oscillation. If you recall Dan N7VE’s presentation on filters that I referenced earlier, he talks about how ringing in filters is caused by abrupt phase changes at the edges of the passband. The cure, when designing them, is to limit the Q in any one stage. Similarly, if you experience ringing in your regen, backing away from the critical threshold of oscillation will lower the Q of the circuit, and should solve the problem. Fascinating. I’ll be interested to hear if any other regen operators have experienced this. My guess is this would be less likely to happen in a regen that utilizes a bipolar transistor for the detector (or combined oscillator/detector if it’s just one device, unlike this design).

I had to try a shot from a lower angle, for that authoritative look. When I’m spinning that big old dial and listening to CW, I can almost kid myself that I’m intercepting enemy broadcasts for the valiant code-breakers at Bletchley Park.  In reality, I’m usually just listening to some ham tell some other ham what the weather is like at his QTH! –

The rear panel (thanks again, Front Panel Express) –

I like this receiver as it is, with the partially open chassis. From using The Sproutie, I have become used to seeing the vanes of the variable capacitor rotate as I tune the band, and I like that. I like seeing these vintage radio parts in action. However, I did learn from The Sproutie that whatever isn’t covered picks up dust – and when you’re living with 3 cats, 2 of whom are long-haired, a lot of cat hair too. I designed this receiver so that it would fit any standard 19″ enclosure that is also 6RU (rack units) or more high. The first plan was to make use of a hack (as the kids call it) of an IKEA product to make a low-cost rack cabinet. The IKEA Rast nightstand is the right size, and only costs US$14.99. For that, and the cost of a pair of rack strips, you can have a rack cabinet that is either 6RU or 8RU high, depending on how you construct it. A Google search on “IKEA Rast rack cabinet” or similar will yield a lot of sites and info on how to do this useful mod.

That was my plan for this receiver until I came across nice-racks.com.  David Tatelbaum makes beautiful studio racks out of his workshop in Massachusetts. He uses furniture-grade pine, though he will use other woods if you request them. The mahogany racks look gorgeous (but they do cost a bit more, of course). From his website –

“Nice-Racks are constructed of solid Pine furniture-grade panels…not just pressed wood or particle board covered in a laminate like some studio racks, but 100% real wood. The panels are cut to size and the components joined together securely using pocket-hole construction and self-tapping pocket-hole screws. The front sides and top edges are rounded, then the racks are sanded and stained. The finish is a clear matte enamel, scuff sanded between coats, to preserve the look and feel of real wood. Finally, hardware is installed and the fully assembled rack is boxed up and shipped out to its new home.”

After finding his site, I was hooked.  Yes, it was going to cost more than the cheap IKEA hack but at some point during the design and construction of this regen, I decided that I wanted it to look really nice, and expense was going to be a secondary concern. I was going full-hog on this. Besides, it took me over 6 months to plan and put together and spreading the cost over that time, the cost per month for my hobby was actually quite reasonable – especially if I take into account all those movies and dinners I didn’t go to because I was at home building! Incidentally, David’s racks are most definitely not expensive. When you consider the cost of your standard rack cabinet – the ones you find in music stores that are made of heavy particle board and covered in black veneer, his racks compare in price very favorably – and they are vastly nicer. They’re not ideal for the rough life of touring but for a home studio, they are perfect – and very good-looking.

OK, so time for the big reveal. This rack cabinet makes The Sproutie MK II look so great –

David also fitted rack rails to the top half of the cabinet at the rear, and supplied a 3RU-high steel panel to help enclose the receiver, and hopefully keep the cat hair away. On the left interior side you can see the recesses for the self-tapping pocket-hole screws that hold the whole cabinet together –

And in case anyone ever wonders who made this fantastic cabinet for my regen, David left his mark. What a quality job! –

The National HRO gear box does have a small amount of backlash – even when I apply as much tension to the anti-backlash gear as my poor little fingers can manage. At first, the backlash was something like 1 – 1 1/2 dial divisions. After increasing the tension on the anti-backlash gear as much as I could reasonably easily manage without the use of tools, the backlash, though still there, decreased to about 1/2 a dial division. It is a small amount, and also predictable, so not really a problem. For the purposes of dial calibration, I always turn the dial in the direction of increasing frequency before taking a dial reading. This ensures consistency in the readings.

Some videos of The Sproutie MK II in action. In the first one, the  towels are on top because Sproutie, my 3 1/2 year-old kitty (aka Sprat The QRP Cat) likes to sit on top of it, and I don’t want her claws to do to the wood what they have already done to my leather sofa –

The Sproutie MK II on 49M, 41M and 40M (though mainly 49M) –

There are some more videos of the Sproutie MK II, showing how a regen can be used in exalted carrier mode to enhance reception of weak AM stations, and on the 25M band, in this slightly more recent post.

There are a couple of things about my Sproutie MK II build that I’d like to change. The first is that, especially at the higher frequencies, the set is slightly sensitive to physical shock. A knock on the cabinet will shift the frequency slightly. I don’t recall noticing this effect with the original Sproutie, although to be fair, I didn’t do as much listening to SSB and CW with it as I do with the new receiver. I think one reason for this slight frequency shift may be the fact that the thick wires connecting the 2 stators of the main tuning capacitor to the coil socket are longer than in the original Sproutie. Although the effect is only slight, it is there, and that bugs me. It may also have to do with the much larger chassis, meaning more metal in the vicinity of a tuned circuit, that flexes when a physical shock is applied. The more I think about it, the more I think this second factor is the main reason. In practice, it is not a problem, but it is there, and I’d like to reduce it, if not eliminate it completely. Fixing a bottom plate to the chassis may help in this regard. Incidentally, banging the desk on which the Sproutie MK II is sitting has no effect. The rubber feet probably help a lot.

The above phenomenon is responsible for an interesting ringing effect that happens occasionally when the regen is set close to the critical point for receiving AM. It only happens with the internal speaker, so is being caused by sound from the speaker vibrating the main chassis. I did mount the internal speaker on small grommets, but this didn’t cure the issue. I have been looking for a reason to purchase a Palstar SP-30B external speaker, and this may be it! This is what the ringing effect sounds like –

The second thing is that, because the cabinet is wood, the receiver is not completely shielded. This would be useful were I to wind a coil for the 2-3MHz region and use The Sproutie MK II in conjunction with crystal-controlled converters to cover specific bands. This is a Regenorodyne approach, like Gary WD4NKA’s inspiring Regenerodyne receiver here. It would also be nice to reduce the possibility of picking up very local QRM in the shack. I could achieve better shielding with my Sproutie MK II by either simply housing it in an all-metal rack cabinet, or by cladding the interior of the existing wooden rack cabinet with thin metal plate or mesh. There is absolutely no hand-capacitance effect when using the set, due to the metal front panel, but when my cat Sprout jumps up on top of it (as she often does) the frequency shifts by about 20Hz. This is also due to the lack of shielding on top of the set. Again, it is not much, but it is there.

Sproutie (aka Sprat The QRP Cat) and The Sproutie MK II. Her contribution to the dial calibration of this receiver was carefully knocking the plug-in coils off the top of the receiver and watching them hit the floor.

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