Dave Richards AA7EE

August 25, 2014

A Huge Compliment From Dashtoons – And A Variable Capacitor Offer

I’m sure you’re familiar with Jeff Murray K1NSS. He’s the man behind Dashtoons, those ever-so-creative and mirth-inducing ham radio cartoons and funnies that appear on many a happy ham’s QSL card and in print, on websites – in fact, wherever a good clean piece of chuckle-creating ham radio artwork is needed. Jeff is well-known within the ham community (and he drew comic strips for print publications in the past) so seeing this today, fresh from Jeff’s pen and creative mind had me, as my fellow Brits say, truly gobsmacked (in a good way). It got such a laugh from me, as it came just a day or two after I had referred to myself as an old coot in the Ham Radio Operators group on Facebook -

One of the things I love about this image, is that it could almost be an ad out of a magazine taken straight from the 50’s. The typefaces, the layout and the wording are all reminiscent of print ads from the middle of the 20th century – yet the design is not solely mid-century. There is something contemporary and clean about it as well, and it is obviously executed with modern tools. Great stuff!

Jeff’s site is here and it’s well worth a look, if you haven’t had a gander at it yet (as some of us Brits are wont to say). I’m even featured on his home page for the time being. Aww shucks! Jeff is available for commissions, is surprisingly affordable and although I haven’t asked him, perhaps he wouldn’t mind drawing or designing non-ham things for you if you have the need? You can always ask. Thank you Jeff – you’re the best!


Now on a different tack, I have a couple of air-spaced variable capacitors that are surplus to my requirements. I’d like to pass them along to someone who can use them, for the price of shipping. They have ceramic insulators and what look like aluminum plates. They wouldn’t be ideal for VFO’s, due to the single bearing and the aluminum plates, as opposed to the double-bearings and brass, or nickel-plated brass that are preferred for very high stability circuits. Also, the bearings in them have quite a bit of friction, even when lubricated. There are actually no bearings in these variable capacitors. From what I can tell, the spindle and the frame around it are in direct contact with no bearings. The spindles do turn and the rotation is smooth, but there is a fair amount of friction. It can be a little hard to turn the spindles by hand but when you put a knob on them, they rotate with no problem. They are identical, with a maximum capacitance of 140pF each. The best way I can think of to describe the rotation is “smooth, yet with a fair amount of friction.”

Although these would not be ideal for the main tuning on a receiver or transmitter, I’m thinking they would work well in a situation where they could be set and left – where they were being used like trimcaps. They’d be great for the trimcaps at the base of an antenna, where they could be set once and left. If you put a knob on them, adjusting is not difficult at all – it’s just that they don’t have that silky smooth feel you’d want for a tuning control. I’ve done my best to describe them accurately and will mail them anywhere in the continental US for $3 (preferably via Paypal) for both of them. That should cover the shipping and the Paypal fee. Please don’t ask if you’re outside the continental US – I’d like to keep this quick and simple.  In case there are several people wanting these, don’t send any money until I tell you. Send an e-mail first to let me know you want them – I’m good on QRZ. If you leave a comment under this post, that will work too, as the system will send me an e-mail notification.

I know they’re only a couple of parts, but I don’t like having components lying around that I know I’m not going to use.

That’s all for now, as The Sproutie is calling and I have some listening to do :-)

EDIT – The variable capacitors are spoken for. Sorry about that!


August 18, 2014

The HumanaLight – A Flashlight That Uses Your “Dead” AA Batteries

A couple of weeks ago, I was spending a very pleasant hour or so waiting in the front yard for the mail carrier to deliver some packages of vintage radio parts I had ordered a few days earlier. My neighbor’s cat Stephen was lounging around with me, and it was one of those perfect afternoons where time almost stands still. It was warm, with a slight breeze and as Stephen and I lay on the garden path looking up at the sky, I nearly forgot the reason for my being out there in the first place.

Eventually, the mail carrier arrived and Stephen took off. He’s an indoor/outdoor kitty, so mistrust of humans he doesn’t know is a valuable trait. The mailman handed me two packages packed with vintage dials and other parts – and another, smaller packet from my friend Thomas Witherspoon K4SWL. Inside was a kit to build the HumanaLight – a flashlight that uses the residual energy in depleted AA batteries to provide useful light for much longer than would be possible without this neat circuit -

The HumanaLight is based on the “Joule Thief”, a self-oscillating voltage booster that boosts the low voltage from a nearly depleted AA battery in order to light an LED. It does this, of course, at the expense of a greater current draw from the battery but it’s not as if this energy was going to be used otherwise.

Thomas is the founder and director of Ears To Our World, a non-profit organization whose main goal is to empower people living in extreme poverty or war-torn areas of the world by distributing self-powered short-wave receivers to them. It may sound like a simple thing, but for people living under very difficult circumstances, access to reliable news and information from areas directly outside their own can be a lifeline.  This page explains it more succinctly.  Many of the radios that ETOW distributes incorporate LED flashlights, and it was noticed that this feature of the radios is very popular. If you don’t have reliable electrical service, a flashlight that can be powered by hand-crank or batteries charged by solar cells is a very useful thing to have.

The HumanaLight was inspired by the LED lights on the self-powered radios distributed by ETOW. It’s a neat idea – a little LED light that is powered by a novel power source – the residual energy in nearly-depleted AA batteries. When the voltage in the AA cells you are using to power your portable radio, camera, or other device, has dropped so low they will no longer power it, there will most likely still be enough energy  in them to run this little flashlight for a useful length of time.

The HumanaLight comes with an easy to follow set of step by step instructions for assembly. It would be an ideal kit for a beginner -

Stephen strolled along to see what was going on and decided to inspect. Luckily, it passed the whole process without a scratch -

Taking a brief break from the rigorous quality control process -

Assembly is simple – just a few components to solder into the board and bingo – you’re done!  The kit comes with two white LED’s – a standard size one, and a jumbo one. You also have the choice of mounting the LED either with the leads bent at right-angles so that the LED points forward like a flashlight, or you can solder it flush with the board so that it points upward. I couldn’t decide, so I didn’t solder it in at all for these pictures, just placing the LED through the mounting holes without soldering (I later decided on using the jumbo LED and soldering it in flashlight-style).

For comparison, I first plugged in a fully charged NiMH cell with an unloaded voltage of 1.35V. You can’t really get an idea of relative brightness from these photographs, as the LED completely blows out the highlights but here’s the picture anyway -

I then tried an old battery that measured 0.76V unloaded -

You can’t see it too well in the picture, but the “dead” battery gave noticeably less intensity. However, if I was in such a situation that I needed an emergency light, and all I had were a few nearly exhausted batteries, I’d be glad for this much light to see my way around. I had another cell in a similar state of depletion, but no others to try. I have read comments from others who tried AA batteries with unloaded voltages of ~0.4V that didn’t work. This circuit does usefully boost the voltage available from a near-depleted cell but it obviously has limits. A cell with an unloaded voltage of ~0.7V isn’t useful for much though, so it’s great that you can use the HumanaLight to get some useful emergency light from it.

The board has a handy hole at the opposite end from the LED – no doubt for a lanyard or suchlike. You could also use it to hang the HumanaLight on a nail on the wall for easy access during an emergency. It would be fun coming up with an enclosure for this – perhaps some thin-walled tubing. I have left mine as is. I plugged a freshly-charged cell into it and switched it on Friday night. Although not an intense beam (it is, after all, a single LED) it raised the ambient light level in my room enough to make it a bit harder to get to sleep, so the next morning I moved it into the hallway where it remains. I’m keen to know how long it lasts.

The HumanaLight is available from Universal Radio here. With circuit design by Gregorgy Majewski and board layout by David Cripe NM0S.  It’s a neat kit and if, like me, you believe that shortwave radio is still a very relevant and useful way to get news and information to people living under very difficult circumstances, purchasing it is a great way to contribute to the cause.



August 6, 2014

N8RVE’s WBR Regen Receiver

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I’ve been chatting with John N8RVE via e-mail for a while now. He built a little receiver that I dubbed “The Rugster” - it’s a direct conversion receiver consisting of a standard NE602 front end, with a “poor man’s varactor” (1N4001) to tune the bottom 50KHz of 40M. The AF stages and narrow filtering are provided by the 4SQRP Hi-Per-Mite filter.  John’s Rugster initially drifted a little, then when he used NPO caps in the frequency sensitive  parts of the circuit, the drift issue cleared right up (funny how that happens!)  He was very happy with his Rugster, as am I with mine.  It’s always great to hear of fellow homebuilders successfully completing projects.

More recently, John built a WBR regen receiver with a FAR Circuits board that he picked up at Dayton, and sent along some pictures of the final receiver. Talk about a neat and original enclosure – he used a piece of plexiglass and a reticle from an oscilloscope -

That’s a neatly wound toroid John -

John says that it sounds great, though he uses an outboard amp, as the audio level was low.  I’m thinking it shouldn’t be too hard to construct a one-transistor pre-amp ugly-style, so that this receiver can pack a little more audio output.

Great job John, and thank you for sharing your success with us!

May 11, 2013

The NA5N Desert Ratt 2 Regen

EDIT If you’re thinking of building the Desert Ratt 2, although the pictures in this post are numerous and quite large, I do recommend reading all the text too, as I have included what I thought were relevant details on the construction as part of my narrative. Also make sure to read the comments and replies.  Previous blog-posts have taught me that readers often ask pertinent questions, so you may be able to glean a little more information from them too.  In fact, just before I wrote this, Paul NA5N made a comment which includes a usefiul piece of information about the 2 x 1,000pF (0.001uF) capacitors in the regen stage.

EXTRA EDIT – Please read the update at the end of this post, after the videos.

I’ve been wanting to build NA5N’s Desert Ratt regen ever since I first found his very attractively drawn schematic for it online. I then found the updated version, called the Desert Ratt 2, and a very good description of how the circuit works – all of these documents available on Paul’s website. What more could an avid regen builder want? Not much, it turned out. Late last year, when N2CX and N2APB dedicated an episode of Chat With The Designers to the Desert Ratt (and to the subject of regens in general), I just had to listen and of course, it fueled my interest in building the DR2 even more. The whiteboard for this particular episode of CWTD is here, and the podcast audio is here.

The WBR was a successful regen for me and while it worked well on SSB/CW, it didn’t seem to quite have the gain with AM stations. This makes sense, as a regenerative detector has to be set below the point of oscillation for AM reception, at which point it has less gain than when it is oscillating (which is where you set it for SSB/CW reception.)  Even so, I had read that bipolar transistors tend to work better as regen stages for AM, as they have higher gain when not oscillating. The search was on for such a receiver, and this was one of the key deciding factors in building the DR2 for me. In fact, Paul has mentioned (I forget where I saw it, as I have done so much reading on this receiver) that the Desert Ratt doesn’t do so well with SSB/CW as it does with AM. My experience with it backs up this assertion, thought it’s a pretty neat receiver for AM.

In particular, I wanted a receiver for covering the 49M SW BC band as although my Elecraft K2 covers a few of the BC bands, 49M is not one of them. There were a few things I found interesting about the design. The use of a phase splitter transistor to convert the single-ended output of the detector to a balanced output in order to drive the LM386 in differential mode was novel. Paul talks about how much RF is flying around inside regen receivers, and how the common-mode rejection of the 386 when used in differential mode can be advantageous in such an environment. I was also intrigued by the detector consisting of 2 germanium diodes – I think I was just looking for an excuse to build something with Germanium diodes again to remind me of my crystal-set building days as a kid :-)

If you look at the schematic of the DR2,  you’ll see that one of the changes in the design from the original DR is that instead of a variable capacitor, it uses 1N4004 diodes as varicaps. I have a bit of a “thing” for nice air-spaced variable capacitors, and I had in mind a nice Millen 50pF capacitor that I picked up on eBay for a very fair price last year. Combined with a 6:1 reduction drive, it made a good combination with a very useable tuning rate for tuning in AM stations.

Anyway, I’m getting ahead of myself here. I did make a few changes to the original schematic for my version, so allow me to introduce my rather wobbly circuit diagram -

The differences between my schematic and Paul’s are as follows -

- I added an RF attenuation pot at the antenna input. After building the DR2, I found that using a relatively short piece of wire indoors as an antenna was causing a lot of common-mode hum.  On top of that, I wanted to be able to increase the signal level into the receiver with the use of my regular outside antenna (A 40M dipole fed with 300 ohm balanced feeder.)  Using the attenuation pot allowed me to use the large outdoor antenna without overloading the receiver.  Use of my outdoor antenna created enough separation between the receiver and antenna that the hum problem almost entirely disappeared.

- Earlier versions of the Desert Ratt included instructions for winding the coil on a plastic 35mm film canister and on an IC shipping tube. The DR2 schematic doesn’t include such instructions, but I wanted to use a toroid, so I experimented a bit and came up with a scheme that seems to work OK.  I used a T68-6 former and the turns info is on my schematic above – a T50-7 would take up a little less space. More about this later.

- I had a few 2-position center-off switches that I wanted to use, so I used one of these for a bandswitch instead of the SPST switch in NA5N’s DR2 schematic. I had originally thought that using the 50pF tuning capacitor with no padding would make the upper limit of frequency coverage too high, resulting in too large a frequency swing in one band, but there must have been more stray circuit capacitance than I had anticipated, as the coverage with no extra padding was about 7.3 – 13MHz. This band became the center position.

- I was attempting to power the DR2 from my shack power supply, which is about 45AH of sealed lead acid batteries with a float charger constantly connected.  This also powers my K2, and the DR2 was picking up processor noise from the K2, as well as a low-frequency “burbly” kind of noise of undetermined origin. The problem went away when I powered the receiver from a separate SLA. but I decided to add extra filtering to the power line anyway.  I found that a 1mH choke as well as a 1,000uF electrolytic almost (but not quite) got rid of the unwanted interference on the power line.  For good measure, I added a 0.01uF RF decoupling capacitor across the power line at the input connection.

- I added an AF preamp stage directly after the diode detector to ensure enough power to easily drive a speaker – even with weak signals.

- The inputs to the LM386 are the opposite way around from the way indicated in NA5N’s DR2 schematic.  With the inputs connected as shown in Paul’s diagram, the LM386 emitted a loud screeching sound.  Swapping the inputs cured this. I was not the only person who had this problem, as I discovered from this post in the GQRP Yahoo Group (you need to be a member of the group to read the post).

-  I left pin 7 unconnected. I don’t understand the way that NA5N has it connected to the junction of the series resistor and capacitor connected between pin 5 and ground in his diagram.  Most circuits that use pin 7 call for a decoupling capacitor direct from pin 7 to ground (usually about 10uF).  This helps reduce large signal distortion, though Paul does say that in this application, it may not do a great deal to help and is therefore optional.  I elected to leave it unconnected.

Now for some pictures.  I didn’t want to spend a lot of time constructing an enclosure, so decided to make a simple PCB L-shaped chassis and build the circuit directly onto that.  With the variable capacitor mounting bracket, it still ended up taking quite a while to construct though. All my projects begin like this, with the main components and control being laid out on the front panel, while deciding on the basic layout -

I’ll spare you the words at this point and apologize for all the pictures that are about to come. If you’re living in a remote area and are still relying on dial-up, then I feel a bit sheepish about the sheer number of images to follow!  I’ve talked before about constructing enclosures from PCB material, so won’t repeat that information here. As well as constructing the chassis from PCB material, I also made a mounting bracket for the variable capacitor and a tuning pointer to attach to the reduction drive with 2 small screws – all from double-sided copper-clad laminate.

I applied several thin coats of lacquer from an aerosol spray.  It was sprayed from a distance, resulting in a light, and stippled coating, which you can see in these pictures. I’d rather apply too light a coat than risk overdoing it. The downside of this is that oxidation will being to affect the appearance of the copper fairly soon. Oh well. The capacitor mounting bracket received a thicker coat. You can see the smoother, shinier finish.

I got the 6:1 reduction drive from Midnight Science. A number of others sell them, and one place that springs to mind is Mainline Electronics in the UK. They are the suppliers for Jackson Bros components (I think they have the rights to manufacture and sell the parts).  They sell on eBay using the name anonalouise.

The enclosure looked a little bit different by the time the DR2 was finished, as the hole for the nylon toroid mounting hardware hadn’t been drilled in the base at this point.

Look at that gorgeous variable capacitor!

A close-up view of the Millen 21050 50pF air-spaced variable capacitor and mounting bracket. This component is silver-plated (the vanes are probably brass), and has double bearings and a ceramic base. It is a very nice variable capacitor, and had never been soldered to before being used in this project. It is at least 35 years old – most likely older!

Boy, was I glad to finish the chassis so that I could start work on wiring it all up.  I decided to build the AF amp first and work backwards, my thinking being that the AF amp would be relatively straightforward. The act of touching the input with a metal screwdriver and hearing a hearty buzz in the loudspeaker would give a welcome psychological boost! If I started by building from the antenna end, I’d have to wait until the entire receiver was built before getting any clue as to whether it was working.

Here’s the chassis with the LM386 amp, the 2N3904 phase splitter, and the 2N3904 preamp built. As has been the case with all my projects since I started using then, I used W1REX’s wonderful MePADs and MeSQUAREs to build the circuit -

Here’s a close-up. The 2N3904 preamp is just below the 6:1 reduction drive, and the 2N3904 phase splitter is to the left of the LM386.  The 100uF capacitor that decouples the supply line to the LM386 straddles it. I read that it is best to ground it to pin 4 instead of to some other point on the chassis to avoid instability, hence the reason for this placement. The other electrolytic that is straddling the chip is the 10uF capacitor between pins 1 and 8 that sets it to the maximum gain of 46dB. The black shielded cable connecting the AF gain pot to the circuit on the PCB is lavalier mic cable.  It has 2 conductors, each of them in it’s own shield, which is ideal for wiring up potentiometers. It is fairly thin and very flexible. I use it in all my home-brew projects. I bought it from a local pro-audio store which recently closed down, so will now need to find another supplier.

In this view, you can clearly see the extra DC supply line filtering that I added, consisting of a 1mH choke in series with, and a 1,000uF electrolytic across, the DC supply. After seeing these pictures, I noticed that there wasn’t very much solder on the joint connecting the choke to the power jack, so I re-flowed the joint and melted a bit more solder onto it.

The power indicator LED’s main function is as a voltage regulator. NA5N marked the various voltages on his schematic for the DR2, and I chose an LED with a forward voltage drop to match those voltages as close as I could.  A green LED in a variety pack I got from Radio Shack had a forward voltage drop of 2.1V, which seemed about right.  The 1N4148 had a forward drop of about 0.65V.

The next stages to be built were the detector and impedance converter/buffer stages.  The description of the DR2 on NA5N’s site gives more info on these stages (as it does for the whole receiver). I couldn’t be sure these stages were working, but bringing my finger close to the diodes resulted in a pleasing cacophony of stations in the headphones – and at a louder level than in doing the same to subsequent stages, so I figured there was some detection/amplification going on :-)

I didn’t know how many turns I was going to use on the toroid, but using the calculator on W8DIZ’ site and an online resonant frequency calculator, I figured that 36 turns on a T68-6 should be a good starting point for the whole winding from pin 3 to pin 6. In Paul’s version, with the coils wound “traditional style”, the tickler winding was about 1/3 of the whole winding.  Coupling between windings is tighter with a toroid than a “regular” coil, so I reduced the number of turns on the tickler. I found that regeneration was occuring at only about 25% rotation of the regen pot, so further reduced the number of turns. Using the turns shown on my schematic at the beginning of this post,  the regen stage moved into oscillation at anywhere between 40 and 50% rotation on the pot, so I left it at that. For the same reason of tight coupling, I used fewer turns on the antenna winding too and because I am using an outdoor antenna, could probably have used even fewer turns.

The toroid was fixed to the PCB with nylon nuts, bolts and washers that I got from my local Ace hardware store.

Here are some pictures of my Desert Ratt 2 with the circuit finished -

The red wires running along the back of the front panel are the regulated 2.1V and 2.75V lines.  I would have run them on the main board but ran out of room due to lack of planning, so went vertical.  Incidentally, although I refer to the 2 regulated lines as 2.1V and 2.75V,  the exact voltages aren’t important.  That’s just what they turned out to be in my case.

The RF amp and regen stages can benefit from transistors with high hfe. I got a cheap Harbor Freight DMM that measures hfe from an eBay vendor for under $6 including shipping.  hfe varies depending on the collector current, but I was doing this mainly for comparative purposes rather than absolute values, so the fact that I didn’t know what value of collector current was used to measure hfe in this cheap meter didn’t matter. It just so happened that my 2N2222A’s tended to have higher hfe than my 2N3904’s, so I ended up using a 2N2222A that measured in at hfe = 203 for the RF amp, and a 2N2222A with hfe = 223 for the regen stage.  The other stages don’t require high-gain transistors. NA5N talks about it in this post on QRP-L from 1999. Bear in mind that he was talking about the original version of the Desert Ratt in this post (just so you don’t get confused when he identifies the various transistors).

I did promise that I’d give a bit more detail on the toroid. Mine was wound on a T68-6 former. The main winding was 30 turns tapped at 27 turns from the top (3 turns from the bottom). The antenna coupling winding was 5 turns.  All turns are wound in the same direction. I used 26 gauge wire, but the precise gauge isn’t important. 26 gauge was narrow enough to easily fit all the turns on the former, yet stout enough to lend some stability to the oscillator, as the toroid isn’t sitting close to the board, and the leads are relatively long. When putting taps on coils, I used to not cut the wire i.e. I would simply make a loop in the wire, twist it, tin the twisted part and keep on winding.  Now I find it is easier to treat them as 2 separate windings connected together. If you can get heat-strippable wire, please do – it makes winding toroids so much easier and more pleasurable.  I wound the first winding of 27 turns, stripped and tinned the end, then stripped and tinned the end of another piece of wire, twisted and soldered them together, and carried on winding the last 3 turns in the same direction (this is important).  The separate antenna winding of 5 turns is also wound in the same direction.  I’m afraid I didn’t write down (or if I did, I have since lost it) the lengths of wire used. I did notice that the turns calculator on W8DIZ’ site (linked earlier in this post) was quoting lengths that are too short for the T68-6 former.  All you have to do is wind one turn around your former, measure that length, multiply it by the number of turns you’re going to wind, add an extra inch or two for the leads and, as we say in England, Bob’s yer Uncle and Fanny’s yer Aunt (meaning – you’re home free!)  When winding toroids, I often find that the first 1 or 2 turns aren’t quite as tight as the rest so when I’ve finished winding, I will unwind one turn from the beginning of the coil, then wind an extra one at the end, to keep the total number of turns the same.  Sometimes I will repeat that exercise a few more times until all the turns are nice and tight.  For this reason, I use enough wire to leave several extra inches at each end.

The next picture shows an anti-hiss filter that wasn’t in the earlier pictures, which I tried and ended up removing due to a low-frequency oscillation it was causing at the higher volume settings.   It was a series 0.01uF capacitor and 4.7K resistor connected from pin 1 of the LM386 to pin 5.   From what I have read, too low a value of resistor or too high a value of capacitor can cause the oscillation. I have seen other anti-hiss filters that used a 0.01uF cap and a 10K resistor, so it is very possible those values would have cured my problem. However, I was near the end of the project and itching to move on, so I just removed it. You can also see the 0.1uF capacitors on the inputs of the IC that have been swapped over to stop the uncontrolled oscillation, and are now crossing each other.  You may not have to cross these caps if you plan your layout accordingly -

Other than the problem with the loud screeching that was solved by swapping over the inputs to the LM386 (my schematic reflects the way the inputs were finally connected), the only other problem I had was with what appeared to be a defect in the 0.001uF (1,000pF) capacitor that leads from the tap on the coil to the emitter of the regen transistor.  I wasn’t getting any regeneration at all but on replacing this capacitor, the circuit broke into a nice loud hiss when advancing the regen pot.

I do have one ongoing issue that I hope someone can shine a light on for me, and that is a loud crackling sound when adjusting the tuning capacitor. At first, I thought a dirty rotor connection was the problem, but it only happens when extra padding capacitance is switched in by the band-switch   With no extra capacitance switched in, the tuning is smooth, but on the lower frequency bands, the receiver crackles when being tuned.  I need to try bypassing the band-switch and soldering the padding capacitors into circuit in case the switch is the problem. I’ll report back when I’ve done further work on this.

Incidentally, the main tuning range on mine covers approximately 7250 – 13000KHz.  Switching in a 47pF capacitor changes the range to 5825 – 8050KHz. I’m a bit limited with my receiver and test equipment here, so haven’t yet been able to determine the coverage of the lowest frequency band.

When first listening to the DR2, I had no idea what frequency I was listening to – only that I was probably somewhere between 5 and 12 MHz. I had no antenna connected (and at this point, hadn’t even built the RF amp stage) but started hearing CW. Lo and behold, it was Hank W6SX 180 miles away from me in Mammoth Lakes, CA. His CW signal was coming through well and in fact, this was the only time I have received CW in a satisfactory fashion on the Desert Ratt. There was no antenna – he was being picked up directly by the toroid.  Any concerns I might have had about the sensitivity of this receiver would have been immediately allayed.

I know the main question that is probably on your mind is – how does it sound, and what is it like to use? How does it “handle”? There are some videos of my Desert Ratt 2 in action at the end of this post. Apologies for the poor video quality, but my only video camera is 10 years old (and has a faulty CCD sensor). You’ve probably read articles about regens that describe the many and subtle adjustments that need to be made when tuning a regen in order to coax maximum performance from it. If you haven’t operated a regen before or if it’s been a while, it does take some time to get the hang of getting the best out of it. As you get further away from the setting of the regen pot where it breaks out into oscillation you lose selectivity and gain, so you need to try and keep the control set just under the point of oscillation. Loud stations can overload the detector, resulting in audio distortion, so it’s worth keeping an eye on the RF attenuation pot too. Also, if the attenuation pot is set too high (too little attenuation), you may get breakthrough from stations on other frequencies. There’s quite a bit going on to keep under control, but if you manage to keep all controls adjusted well, you can coax some pretty decent performance out of the set. I think this is why regens appeal to some people – we are incurable knob-twiddlers!

Stability is easily good enough for AM reception and with a logging scale fitted to the front panel, I don’t think it would be hard to find specific frequencies, as the majority of SW BC stations stick to 5KHz channels. In my casual listening so far, I have heard The Voice Of (North) Korea on 9435 and 11710KHz, Radio Habana, Cuba on the 49M band, Radio Australia on the 31M band, coastal station KLB (South Korea) on 8636KHz, the BBC World Service (forget which band or frequency), China Radio International on 9790KHz, WTWW on 5830KHz, and a number of other evangelical Christian stations (sorry, I tune them out and don’t pay them much attention.)

To sum up, you can definitely have a lot of fun and engagement with the bands on this set.  Being a regen, it is not the easiest receiver to operate, but you shouldn’t let that put you off. The best analogy I can think of is to reference the way that although an older British sports car may not have the finesse and performance of a newer sports model, it’s a lot of fun, and it’s lack of suspension gives you an exhilarating feel for the road that the more expensive cars cannot.

The Desert Ratt 2. A logging scale fixed to the front panel would make frequencies in the SWBC bands easy to find. I must do this sometime :-)

Please note that in the following videos, an MFJ-281 ClearTone speaker was used. My understanding is that this speaker has a slight resonant peak at around 700Hz (helpful for CW) and a relatively restricted overall bandwidth that is good for communications applications. This probably means that it’s not optimum for getting the maximum fidelity from an AM SW broadcaster (not that those stations have a lot of fidelity, but they tend to have a bit more than your average SSB transmission). On top of that, the audio was captured with the built-in mic in my old Canon A80 compact. Please don’t judge the quality of the Desert Ratt 2 audio from these clips. It’s better than this! I’m working on a few audio only recordings that will better demonstrate what the DR2 sounds like, and will put them up in the next blog-post (hopefully within a week or so).

Update – It has been about a year since I built my version of the Desert Ratt 2 and I feel compelled to provide an update. Whenever I first build a project I am often so thrilled that it works at all, that I tend to gloss over any shortcomings, particularly in my blog write-ups. Some of this is due to the possibility that any deficiencies are due to my layout and construction, as opposed to a problem with the circuit design. In the case of my DR2, I am still not sure whether the issues arise from the circuit itself or from my construction, as I have only built one of these. I did, however, want to document what I have observed, as my DR2 has laid on my shelf for the past year, largely unused, while I drag my WBR out and take it for a spin on a regular basis. Here are the issues I have observed -

* There is a lot of scratchiness in the speaker when tuning the DR2. This happens on some frequency ranges more than others, but it happens a lot.  At first, I wondered if it was due to inadequate grounding of the rotor plates but I don’t think this is the case. There is a solder tab for both the rotor and the stator, and the rotor is grounded to the chassis by a direct wire. Also, it is a quality Millen variable capacitor, and it is clean (the oxidation has been cleaned off).  I’m still considering the possibility that it as something to do with my variable capacitor, or the way that I have connected it.

* The set does seem to overload very easily on my outside antenna. Breakthrough from other frequencies is a common occurrence. This got me to thinking about the RF amp stage. The instructions call for picking a high hfe transistor to use in this position but thinking about this, I’m not sure why. Surely the purpose of an RF stage in a regenerative set is to provide isolation between the detector and the antenna, with gain actually being undesirable, due to the tendency of the detector to overload? The more I think about it, the more I think that different configuration for this RF stage would be more appropriate.

* Hum, though not always apparent, does still occur from time to time.

A commenter who goes by the name of Mast does mention that the tank circuit is very tightly coupled to the collector of the regen transistor. I’ll cut and paste his comments here, as I now wonder why I didn’t pay more attention to his input at the time,

“A nice schematic for general use. But the tank circuit is tightly coupled to the collector of the regenerative stage. You will suffer a lot from changing internal stray capacitances of the transistor when setting the regen level. And strong SSB signals will change these capacitances too, causing an unintelligible reproduction of SSB signals.”

At this point, the DR2 has gone back on the shelf while I move on to planning other projects, but I’d be very interested to hear what the experiences of others have been with this circuit.  I know there are folk who found N1TEV’s beginner’s regen to be a little hard to tame – and the DR is based in part on that circuit.  In contrast, both my WBR’s are well-behaved, and have been used regularly since I built them.

April 17, 2013

My Ongoing Pre-Occupation With High Quality Air-Spaced Variable Capacitors

I’ve blogged before about air-spaced variable capacitors.  I’ve always liked ‘em, but I think my understanding of what makes a good one is maturing a little more. I was the winning bidder on a really nice-looking specimen on eBay a few days ago.  Ever since placing the winning bid, I had been excitedly looking at the pictures of it posted by the seller. It looked great. How exciting when it arrived in the mail yesterday and I got a chance to see it “in person”, as it were!  I got it for $11.50 and I think I scored -

It is NOS (New Old Stock) meaning that while it is old, it has never been used. Surprisingly, there seems to be quite a few of these high-quality NOS caps still floating around. Here are the specs for this series of variable capacitors from Hammarlund -

The cap that I scored has nickel-plated brass vanes. Brass is good, as it expands and contracts with changes  in temperature less than aluminum does (the other main material from which variable capacitor rotors and stators are made.) Also good are the bearings on each end of the rotor shaft. I can’t see them, but I assume the bearings are hidden away. It gets better. This capacitor has wide-spaced plates, meaning less change in capacitance with temperature changes than a part with closer spacing. Oh – and this is all firmly mounted on a ceramic base. Ceramic is a great insulator and I’m thinking that this must also be good for the physical stability of the component with regards to changes in temperature.

I just noticed something. As you rotate the shaft clockwise, the capacitance increases. It’s normally the other way around.  An end-stop prevents the shaft from rotating more than 180°, or this wouldn’t be an issue.  This must have been intended for use with a drive mechanism that translated the rotation of the tuning knob into rotation of the capacitor shaft in the other direction. I hope that the length of shaft protruding from the other end is enough for me to connect to, otherwise it might end up on the shelf for a few more decades!

One thing you may not appreciate from these photos is the feeling of solidity. This is a beautifully engineered part. See how the shaft is off-center? This makes for a non-linear relationship between the rotation of the shaft and the change in capacitance.  The change in capacitance occurs in such a way as to make the higher frequencies a little less cramped together, which is what happens with a capacitor where the relationship is strictly linear.

I mean, really – do variable capacitors get much better than this?  I don’t have definite plans yet for this little beauty but if my current interest in regens continues, I can see it paired up with the Jackson Brothers Dual Ratio Ball Drive and Dial I just ordered from the UK and used as the main tuning cap in a general coverage regen receiver – all built on a generously-sized aluminum chassis with front panel. (EDIT – unless I am able to connect the ball drive to the rear end of the shaft, this is not going to happen. Fingers crossed.)

Scroll back up to the top of the page and look at this fabulously engineered piece of American history sitting on top of it’s original box. That’s what it feels like to me – a piece of American history, and I got it for a few bucks. I will feel terribly privileged to be able to incorporate it into my own project at some point, though I’m going to hang onto that box.

Incidentally, while riding around Oakland, I noticed that this commercial space is up for lease.  It would be a good place for a ham-oriented business don’t you think? EDIT – It is now March 2014 and I recently noticed that this space has been turned into a coffee bar – the type that looks like it is part chemistry lab, with much glassware used in the brewing of the coffee.  Aah well – better than being left empty!

March 10, 2013

W9RNK’s WBR Regen Odyssey

About a week and a half ago, I received an e-mail from Rich W9RNK.  After a long period of home-brew inactivity (about 20 years) he decided to pick up the soldering iron and start building again. He said that my post on building N1BYT’s WBR Regen Receiver (the most popular post on this blog by far) had inspired him and I consider that a great compliment. If one of my posts inspires someone to do something they haven’t done before, or haven’t done in a long time then in my mind, it completely justifies having and keeping this blog.

He did get his WBR receiver working after some initial setbacks   It seems that his problems were caused by using a core material for the inductor that wasn’t suited for the frequency. He used a toroid with a blue core, which is quoted as not being suitable for frequencies over 3MHz.  On substituting the recommended yellow color-coded toroid, the receiver started working.  In his write-up, which I link to below, he shows the schematic of 7N3WVM’s version of the tank circuit which includes a 0.22uH inductor from the center-tap to ground.  The QRP-Tech Yahoo Group run by Chuck Adams K7QO made the WBR the subject of an informal group-build not too long ago and I noticed that some of the members experienced problems with sensitivity. Steve AA7U found that adding a choke from the center-tap to ground alleviated the sensitivity problem. Based on his experiments, he determined that the optimum value is around 1uH.  I had no problems with sensitivity, so my recommendation would be to build the WBR as per the original QST article, and to experiment with adding an inductor if you do experience low sensitivity. However, I do wonder why others have had these problems when I haven’t?  In the original article, Dan mentions that the length of the stiff wire connecting the center-tap of the coil to ground should be about 1″.  I was careful to make mine about 1″, as well as to connect it to the ground-plane of the PCB, as opposed to connecting it to some other grounded point on one of the potentiometers or the enclosure. That’s all I can think of but hey – if an inductor works for you, that’s great.

The other main issue Rich had with his WBR was drift.  I hadn’t measured the drift on mine as it seemed to be quite good. However, prompted by his observations, I decided to take measurements on mine today.  From a cold start, it showed by far the biggest drift rate in the first minute (no surprise there) by drifting 120Hz downwards. In the next 14 minutes, it drifted another 190Hz down, for a total drift of 310Hz in the first 15 minutes. In the next hour, it drifted another 240Hz down, and the hour after that, 100Hz.  I would have been interested to see what the drift was in the 3rd hour but boredom, and the lure of other tasks to complete prompted me to stop!  My WBR (which has an AF preamp stage, unlike N1BYT’s original design) still only draws 13mA so when using it, I used to leave it on all day.  I’d find that I could set it on a net frequency, come back an hour or two later and hear little drift, so I’m thinking that had I measured the drift in the 3rd and 4th hours it would have been less still. Not world-class, but not bad at all for a circuit with no attempts made at temperature compensation, and intended just for general listening.

Here is W9RNK’s write-up detailing his odyssey towards a working WBR Regen.  It’s a pdf file, so make sure you have a pdf reader on your computer.

Rich W9RNK – WBR Build

Many thanks to W9RNK for writing this up, so that it can be shared with others. Hopefully it will serve as an inspiration to anyone else who hasn’t picked up a soldering iron in a while.

PS – I do, like Rich, think an AF pre-amp is a worthy addition. I took N1BYT’s advice and used the same pre-amp that he used in his OCR II Receiver (Sep 2000 QST). Here’s the schematic of the AF stages of my version of the WBR -

That’s it for now.

March 9, 2013

TX5K – A Well-Run Operation and an Interesting Island

Filed under: Amateur Radio,Ham Radio,QRP,Uncategorized — AA7EE @ 8:47 pm

Today is the last full day of the TX5K team’s operations from Clipperton Island and they have already dismantled site B.  Site B was mostly CW which meant I had to abandon my hopes of getting them on 40 and 30 in order to achieve a clean sweep on QRP CW for all bands 80 – 10M.  However, getting a single DXpedition on 6 bands is a first for me, and I’m pretty happy with it.

Clipperton Island is an interesting place. In modern times, 4 nations have fought for ownership, partially for it’s strategic positioning, and partially for it’s surface layer of guano (translation – the island is covered in bird-droppings.)

The last attempt to permanently colonize Clipperton ended in tragedy in 1917. I’ll leave you to read about it but as Joel KB6QVI said to me, a film could be made from the drama that occurred on this small island in the North Pacific. Indeed it could, and not much in the way of dramatic license would need to be taken in order to make the story compelling for a modern movie-going audience. The Wikipedia entry about Clipperton Island is here (opens in a new window), but you’ll find a more lively read in this article.

Two things struck me almost immediately about TX5K -

1) It was a well-run DX-pedition. Good operators with good ears.  I’m referring to the CW side of the DXPedition as I almost never use SSB when DX’ing,

2) The ability to see the QSO you have just made on a map on their website, as well as see your QSO in their online log is fantastic.  No waiting for a log to be uploaded – the website updates every 60 seconds and with each of the 6 QSO’s I made, I saw myself in the log no more than 2 minutes after making contact. No more wondering whether to make an insurance QSO.  This kind of technology can only have a positive effect on the QSO rate, although I did hear the op on 40M last night firmly talking to a station that had already made 5 QSO’s with him. Obviously that station wasn’t familiar with the near real-time online log. The software was written by expedition leader Robert Schmieder KK6EK, and sets a new standard for DX-peditions of this size,  IMO.

Here’s how I managed. Got ‘em on 6 bands with 5W of CW to a 66 foot inverted vee with the apex at 47 feet (partially obscured and partially in the clear).  As Justin VE3XTI commented, I sure suck at SSB :-)

John AE5X got a clean sweep on CW from 160 – 10 which, knowing John’s experience, came as no surprise at all.  I pretty much expect that kind of excellence from him!

Aerial photos of the DX-pedition site can be seen here.  Teams who mount these events go to great lengths so that we can have our DX QSO’s, so no whining on the cluster because the entity you want is not currently taking QSO’s in your preferred mode from your part of the world. In fact, don’t treat the cluster as a message board, period.

Cordell Expeditions, who mounted the TX5K operation, are planning an expedition to Heard Island in Antarctica next year. Definitely one to look out for.

In the meantime, I’ve got my sights set on 9M4SLL, which takes place March 10th – March 18th. Thanks for the tip-off Jason :-)

December 31, 2012

The ARRL 10-Meter Contest and Checking In To SSB Nets with QRPp

A few days ago, Bryan Herbert KE6ZGP, posted on Facebook that he’d come first place in his section for Single Op QRP phone in the 2011 ARRL 10-Meter contest and posted a picture of his certificate. I thought it was pretty neat-looking and gave him my congratulations, telling him that I was envious, but happy for him, and also noting that I’d never won anything like that, as 2 hour sprints were about the most I had any kind of stamina for.

Then a little over an hour later, the front doorbell rang.  It was the mailman with a few packages for my neighbors and a large brown envelope for me, containing this -

I had completely forgotten entering the ARRL 10-Meter contest.  It was almost a year ago!  I had participated (casually), submitted my log, and promptly forgotten about it.  Now I know that I am by no stretch of the imagination even a semi-serious contester, so figured that there probably hadn’t been many other QRP CW contenders in my AARL section.  On checking the ARRL site I found that there had been just one other. Nevertheless, I was very happy to have this piece of paper, which is already framed and hanging on the wall.

In other news, I have been doing no home-brew – sorry about that. My INTJ mind is either very pre-occupied with something, or not noticing it at all. Currently, I am engrossed with the task of committing as many music CD’s as possible to hard drive in order to de-clutter my living space. It’s all part of a long-term plan for the future which may include living in an RV, or simply another apartment.  Either way, I want less stuff, and 10,000 music CD’s are awful heavy when it comes to moving time. While busying myself with the task of ripping and scanning during the day, I have had the K2, my main station rig, tuned to 40M and in particular, the Noontime Net on 7268.5 KHz. My mind works in strange ways, and for the 3 years I was into CW, that was all I was interested in.  I had spent plenty of time operating SSB (and FM on the 2-meter band) in the past and it no longer held any interest for me – it really didn’t.  Every now and again, I would tune up to the phone portion of whatever band I happened to be in and after just a few minutes of listening, wonder how anyone could remain interested in amateur radio if SSB was their main mode of operation. I like the mental challenge of decoding a CW signal in my head, and that is as much of an attraction to me as the radio part.  Decoding SSB in my head was a skill I learned when very young, so there’s not much challenge there!

Nevertheless, while busying myself with the task of ripping CD’s and scanning all the artwork, I had the K2 tuned to 7268.5 KHz from about 9:30am – 2pm every day to listen to the Noontime Net.  I have never done a lot of listening to nets before and at first, couldn’t quite understand the attraction of checking in to a net on a regular basis when the main purpose of doing so seemed to be to just check in and then not do much else. However, there is a little bit more to it than that, and after a few weeks of listening, I started to get a feel for it and checking into the net became a welcome part of my daily routine. EDIT: After a few months of checking in daily to the Noontime Net, it has become a very welcome part of my daily routine and to amend what I said a few sentences earlier, there is a lot more going on with a net like this than first meets the ear. It is a very well-run net that manages to check in a lot of people every day, while still having time for the occasional bit of friendly chat. It never wanders into the territory of “clique-ness”. The balance between the business of checking in a lot of people, while retaining a sense of camaraderie and connectivity is perfect. KV7L Lynn is the net manager, and along with every single one of the net controllers, is to be commended for pulling off this feat. It’s not an easy thing to do.

The Noontime Net is a traffic net, and traffic is indeed passed on occasion.   After a few weeks of listening almost daily (at first on the WBR regen receiver when I was still fresh out of building that) I began to recognize the regular characters,  including the very distinctive voice of Clyde AA7WC who took early check-ins daily until his recent illness. I checked in a few times, and then having the radio on and listening to the net in the background as I did other things around the shack, checking in on an almost daily basis started to become a welcome part of my daily routine. Many days, I will check in fairly early, and the re-check later.  It’s also interesting to listen to many of the same stations regularly to see how propagation affects how we all hear each other – and this brings me to the aspect of the net that has interested me the most in the last week or two.

I had been checking in to the Noontime Net with my K2’s full output power of 15W.  About 10 days ago, I decided to dial down the power to see whether I could still check in with one of the net control stations.  On CW, you can turn the power down to 100mW, and on SSB, 1W.  I dialed down to minimum SSB power and called Lynn KV7L in Princeton, Oregon. I thought I was running 100mW but forgot that on SSB, even though the K2 may indicate an output power of 0.1W, it is actually putting out 1W. To my surprise, Lynn gave me a 58 report. He is 412 miles from me. I also got a 59 report from a station in Bakersfield, about 245 miles to the south.  Thinking I was running 100mW, I was ecstatic but in retrospect,  a 58 report from a station 412 miles distant when you’re running 1W of SSB is still pretty good.  Since then, I have regularly checked into the net with just 1W and am heard well by KV7L in Princeton, OR, W6FHZ in Reno, Nevada and N7WH in Boise,  Idaho.

I often received unprompted reports of good audio too, for which much of the credit has to go the K2.

All of this has gotten me quite excited about seeing how low I can take the power and still successfully check in to the Noontime Net. I cannot dial the power on my K2 below 1W on SSB,  so the next step is an attenuator.  Even though I have not been doing any home-brew and am concentrating most of my efforts on non-ham radio pursuits, I think an attenuator is in my immediate future.  I would love to be able to tell net control that I am running just 50mW – or even 10mW! Stay tuned to this space.  Maybe I can get something together in the next few weeks. (EDIT – I ordered an attenuator online before this post was even finished – keep reading.)

The upshot of all of this is that although when people think of QRP, they usually think of CW, and the 13dB disadvantage of SSB compared to CW is well-known, you can still achieve things with QRP SSB. Bryan Herbert KE6ZGP has made many great DX contacts with just 5W of SSB (and even FM during 10M openings) and he told me recently how he thinks the potential of QRP SSB is underestimated.

On another tack, I was in Cost Plus the other day and saw a mint tin that was just crying out to have something built in it.  Some people think of electronic gadgets as boxes of “black magic” and indeed, even us hams think of radio as quite magical.  I like to put as many of my mint tin projects in different looking tins as possible, to make them easier to tell apart from each other. I think this tin fits the bill perfectly. What piece of black magic could I build into this enclosure?

My recent experiences successfully checking into the Noontime Net with just 1W PEP of SSB made me keen to see if I could check in with even less power.  The minimum amount you can dial the power down to on the K2 on SSB is 1W, so to get it down further I would need an attenuator.   I was looking for a cheap way to do this without having to build anything, and settled on this 20dB inline attenuator that I got from eBay for $6.99 including shipping -

I like it because unlike the step attenuators in regular enclosures, I don’t have to come up with an extra BNC to BNC cable.  It’s quick n’ dirty n’ cheap. Without setting up a separate receive antenna, the attenuator also attenuates the signal on receive, but as I plan on initially using it to check in with net control stations that are very strong here, that won’t matter.

In theory, when I set the K2 to 1W and connect the output of it to the attenuator, which is terminated in a 50 ohm load, the 1 watt should be attenuated by 20dB, giving me a final output signal of 10mW into 50 ohm, but when I connected the output of the K2 (set at 1W in CW mode) to my OHR WM-2 QRP Wattmeter, the output of which was terminated  in a 50 ohm load, I measured 40mW and not 10mW.  I do believe the meter to be calibrated accurately  so I am not sure what is going on here.

The next step should be to construct my own attenuation pad to verify these results but for the meantime, the Noontime Net was in progress and I wanted to see if net control could hear me. KD7RTE was taking check-ins and couldn’t hear me, but Lynn KV7L in Princeton, OR gave me an S3. He is 412 miles distant – not bad for 40mW of SSB.

I have gotten into the habit of checking into this net with 1W PEP and I think I will continue to do so, but the quick n’ dirty experiment with QRPp was pleasantly fruitful. I kind of wish it was possible to use the front panel control on the K2 to dial the power all the way down to 100mW on SSB, the way you can on CW – or even lower. QRPp is fun! 40mW is flea power, and it’s especially gratifying for a signal of such low power to be copied 412 miles away on SSB.

In other news, it has become harder to operate the radio, because Sprat The QRP Cat has decided that she likes biting the fingerpieces of my Bencher paddle.  I try to put the K2 in test mode so she doesn’t transmit. When she’s not practicing the code, she just likes to get in the way when I’m trying to operate the radio, and steal the spotlight -

November 11, 2012

S9 +10 QRM Problem Solved and a Cat Adoption From HRO

Shortly after making the last blog-post, my radio operating activities were severely curtailed by QRM that registered well over S9 across all the HF bands. It wasn’t continuous but would come and go seemingly at will throughout the day and night – there was never a time when I could be sure it wasn’t going to obliterate whatever I was listening to.  Several times it would appear while I was in the middle of a QSO, and cause me to QRT prematurely. I hoped that the QRM would disappear as mysteriously as it arrived, but after a few weeks, this “hoping” approach didn’t seem to offer as much, well, hope as it had before.

I live in a 100 year-old house that was converted several decades ago to individual studio apartments.  The first step was to verify that the QRM was coming from my building, so I walked around, both inside and outside, with a small battery-operated portable Grundig shortwave receiver. Inside the house, the QRM had a fairly even signal strength, becoming a little stronger as I got closer to the walls. When walking outside the house, the QRM faded rapidly, only becoming stronger as the radio got closer to the outside walls of the house.  I concluded that the QRM was being carried on the AC wiring of my apartment building and was being generated by something plugged into the AC.

I know all of my neighbors, and relationships with all of them are cordial, except for one. She decided a while back that she just didn’t like me, and I tired of trying to make peace. It seems that wherever I go, there’s always one, but that’s a different story :-)  Even though I get along with nearly all of my neighbors, I wasn’t sure how successful I’d be approaching each one individually and requesting permission to go on an RF snooping exercise inside their apartments. It wasn’t really something I fancied doing.

So what to do? I had no idea, and for the next week or so, had partially resigned myself to the idea that I was just going to have to deal with the fact that I was now living in an environment that made my ham radio and shortwave listening activities much, much more challenging. How very frustrating!  Many times in the last few weeks, I had asked myself if anything in my apartment had changed recently and every time  the answer I came up with was that it hadn’t. Then I remembered something.  Recently, I started fostering a sweet and very shy 10 year-old cat called Chala.  You can see her at the end of this last blog-post.  The foster agency with whom I was working gave me an electric pet heating pad for her – and that was at about the same time the QRM began!  It was like a light-bulb going on in my head and of course, it was too good to be true.  But it wasn’t – I unplugged the heating pad and the QRM disappeared instantly.

The level of QRM was so high and so well distributed throughout the whole house, it was hard to believe that a little 9″ square heating pad could cause so much interference, but it sure did.  Luckily,  I don’t think she really needs it anyway. It’s just as well, because it’s not going to be used at this QTH any more.  Any locals want a pet heating pad for free?

Be warned – this pet heating pad will radiate S9+ QRM from the wiring in your house/apartment on all HF bands!

I have been doing very little radio recently other than checking into the occasional SSB net while doing other things, so there is no news of any new home-brew projects I’m afraid   There is nothing planned either, so I may be posintg even less frequently in the future than I have been doing in the past.  My interests are shifting back towards trying to get as much of my music collection as possible transferred onto hard drive in case I purchase an RV and take to the road in a few years. The other thing that has been on my mind is cats.  I’ve begun the steady inexorable march towards becoming a certifiably crazy old cat guy. My new companion, Chala, is a sweet kitty, but she’s very shy. My last cat, Rug, was a lot more outgoing and I miss that. Chala’s great and I derive a lot of of satisfaction from giving her a safe, comfortable home after her ordeal on the streets, but I have been wanting a little more kitty interactivity.

It was with this general mindset that I made a trip to the Oakland Ham Radio Outlet about a month ago in order to buy an 8-pin mic connector. It was also an excuse to browse the magazines and books. While standing at the counter, the employee who was helping me walked out from the back room and was being followed by a little kitten, who was happily prancing around and generally being very friendly to anyone in the vicinity. HRO wasn’t a place I’d normally expect to see a cat, so I was curious to know why she was there.  It turned out that Nick, one of the employees, had discovered her trying to keep warm that morning by pressing herself up against the engine of his truck in the parking lot. He pulled her out, and she spent the rest of the day in the store happily attaching herself to the employees. When she jumped up on the counter, stood on her back legs, put her two front paws on my shoulders and gazed at me, I was hooked. Then when she curled up on the counter in front of me, pressed her little body up against me and started purring, I was a goner.  I asked Mark WI7YN, the manager, what he was going to do with her. He said that he didn’t want a store cat, so had been thinking of asking the customers if they wanted a kitty. Without giving it a second thought I said that I’d take her, bundled her into my backpack and cycled home with her.  So began a love affair with this fabulous little kitty companion -

What to call her?  I wanted a name that reflected where she was found, but anything too ham radio oriented wouldn’t make sense to my non-ham friends (who are most of the people I know.) In the same way that hams have both a regular “civilian” name and a call-sign, this little kitty has her regular name, which is Sprout – as she’s a cute little Sprout!  Her ham radio name is “Sprat The QRP Cat”. I hope the GQRP Club approves -

Sprat The QRP Cat

I still haven’t used the 8-pin mic connector I bought that day but I’m looking at it this way – I paid an $8 fee to adopt a kitty and had a free mic connector thrown in. Thank you Mark WI7YN and the team at Oakland HRO.

PS – Sprat The QRP Cat was not micro-chipped and not spayed.  The vet estimated her age at 5 months. She has since been micro-chipped, spayed and has had her shots. She’s in fine shape!

September 19, 2012

Courtesy Of F5VJD – A Working G4JST/G3WPO DSB80 80M DSB Transceiver!

Filed under: Amateur Radio,Ham Radio,QRP,Uncategorized — AA7EE @ 5:03 pm
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As I’ve explained in earlier posts, my interest in the G4JST/G3WPO DSB80 rig goes back a long way – back to the mid 1980’s in England when I read the description of this little rig in Ham Radio Today and scratched together the money to buy the basic kit. An enclosure was also available but I didn’t have enough money for that as well, so built it into an aluminum enclosure I already owned. That little rig gave me much fun until one day in my apartment in Hollywood in the mid-1990’s when I accidentally connected the 12V power to it the wrong way round and it instantly stopped working. I didn’t have the patience, time or experience to get it working again, so (and it pains me to say this) I tossed it into the trash. There have been several times since then that I have regretted doing that, and since then, the inability to see my DSB80 only served to further memorialize that rig in my mind.

Recently I dug up the reprint of the article that came with the DSB80 kit (I did keep that) and tried to rebuild it Manhattan style – here and here.  The receiver worked as well as I remembered the original working, but I experienced a problem with the transmission of a residual carrier on transmit. After a few weak attempts to cure that issue, I shelved it in favor of other construction projects. It’s a weakness of mine – if something doesn’t work well the first time I switch it on, unless the fix is relatively simple, I don’t always pursue it. I didn’t consider it a failure, as the receiver worked well – and it was wonderful to once again listen to a direct conversion receiver that utilized a diode ring DBM . The TX seemed to work up to and including the final,  so there was really not that much to troubleshoot if I ever wanted to give it another go.

Then a very exciting comment was left by Richard F5VJD on the blog post about my DSB80 build. It read as follows -

“Hello Dave

I also built one of these in 1983 and I still have it… but like you I fried it during a fit of nostalgia.

I do still have the original instruction sheets and the original Ham Radio Today articles which I could copy and send you if you like… and as I can’t really see myself replacing all the fused components in the RX, I would also be happy to send you the radio if you promise to repair and use it. It has some nostalgia value for me because it was the first kit I ever built and I had my first ever QRP QSO using it, so it would be nice if it was back on the air again after all these years.

Let me know what you want to do and I’ll get things started my end.



Well, how do you think I replied? This was a chance to see that little rig again – and to see how another ham had built it too.  Richard told me that he had used the original case suggested by Frank and Tony, so I was curious to see a more “original” version of the DSB80 than mine was.  Richard packed up the mighty little transceiver and even took a picture of him with it outside his home in Northern France to mark the beginning of the journey to it’s new home in California:

About a week later, it turned up on my doorstep in California:

Wow – talk about well-packed! The DSB80 was very well protected with much packing material, and Richard had written his address inside each layer while packing, just in case it became partially unwrapped in transit.  We needn’t have worried, as it made it’s way to me in one piece. It’s just as well that I’m patient, as it must have taken the best part of 10 minutes before I finally saw the object of my desire. What a great looking transceiver! As well as the several address labels in the package (including one taped to the rig itself), there was an envelope inside the enclosure, with a note from Richard and some extra J310’s and BC182’s. The BC182’s are near-equivalents to the BC238’s and BC239’s used in mic amp, AF pre-amp and RF driver.

I could barely wait to open it up and see that circuit board once again:

I could hardly contain myself.  It was so great to see that circuit board that I remembered so well from my youth.  Notice Richard’s ingenious use of Meccano to help support the mounting bracket for the tuning capacitor. I think that Meccano sets were called Erector sets in the US:

Here’s a view from the other end of the rig, showing the input/output bandpass filter, with the 2 inductors wound on T68-2 cores. Fixed to the back of the case, that board with the relay gives full break-in operation:

In case you’re not familiar with the architecture of this rig, or don’t remember my previous posts on the subject, it is a CW and DSB transceiver based around a Mini Circuits SBL-1 diode ring double balanced mixer package.  The SBL-1 was rated down to 100KHz so gives excellent out of band rejection at the design frequency of 3.5MHz. My earlier Manhattan version used an ADE-1 which is only rated down to 1MHZ, but there was not a trace of any out-of-band breakthrough.  Here’s a block diagram and device breakdown:

Block diagram and device breakdown of the G4JST/G3WPO DSB80 80M CW/DSB transceiver, details of which were first published in the March 1983 edition of the UK magazine “Ham Radio Today”.

This DSB80 of Richard’s had been inadvertently connected to 12V with reverse polarity, just as I had done with mine. The first order of the day was to remove the board from the case and, well, make it work again! Richard mentioned that one or two of the electrolytics had exploded, so I knew that at the very least, I’d need to change some of the electrolytics and one or more active devices.  On getting the board out of the case and onto the workbench, one of the big advantages of boards without plated-through holes became apparent – with the help of desoldering braid, it was very easy to remove old components and replace them with new ones. After replacing the big electrolytics that performed service as smoothing capacitors for the 12V supply (one of which had very obviously exploded) I realized that it would be very little trouble to go ahead and replace every single electrolytic. After all, the rig was about 25 years old, and those caps might be getting a bit dry by now.

After replacing all the electrolytic capacitors (even the small signal ones – including replacing the 1uF electrolytic in the diplexer with a polyester cap just for good measure), I connected wires for the volume pot, antenna and speaker, connected a 12V supply (the right way round this time!) turned the volume up and – as predicted – heard absolutely nothing. This was not a surprise as I had a feeling that amongst the devices well and truly cooked would have been the LM380.  This rig used the 14-pin version of the LM380 and I had planned in advance and purchased one. In it went (thank heavens for de-soldering braid!) On re-applying power, I heard hiss in the speaker, and on touching the input to the DBM, I heard atmospheric noise.  It couldn’t be this easy could it? Well yes, it could!  Further investigation revealed that the VFO and buffer were working and the receiver was fully operational.  Not only that, but the transmitter was working too – and without the issue of residual carrier emission that I had experienced with my Manhattan version. Woohoo!

This was the point at which I became a little uncertain what to do next. I still felt that it was not really my rig – it was Richard’s that he had sent to me.  I knew that he had given it to me, but still felt a reluctance to change it too much from the way in which he had built it, for fear I was being disrespectful to the history of this fabulous piece of home-brew. After all  it was the first transceiver he had ever built, with which he had conducted several hundred QRP QSO’s.  Richard put my mind at rest by saying that it had ceased being his rig once it left his house in that brown paper package. He was happy to know that it would continue having a life in California, and wanted me to do whatever I wanted in order to “make it mine”. What a helpful and wise sentiment. I wanted to retain something of the original rig other than (obviously) the circuit board. Richard suggested that perhaps I could fabricate an enclosure from copper-clad laminate and use the original top cover. What an excellent idea!

First of all, I wanted to modify it to cover the entire US band of 3500 – 4000KHz. The original version, being a UK design, covered the UK 80M band of 3500-3800KHz. I used a different tuning capacitor – a 365pF air-spaced variable with a built-in 8:1 reduction drive that I bought new from Midnight Science. I also re-wound the VFO toroid and changed a few of the other caps in the VFO circuit to achieve a coverage of 3485 – 4019KHz.  Even with the reduction ratio of 8:1, this still gives a tuning ratio of over 125KHz per turn of the tuning knob.  In order to help, I added a fine-tuning control consisting of a 1N4001 diode across the VFO tank circuit, acting as a varactor, and tuned with a 1K linear pot. The schematic of the modified VFO, with values, is as follows:

The other modification I needed to perform was to redesign the input/output bandpass filter in order to accomodate the wider US band.  Thank goodness for the software that comes with EMRFD – the program DTC.exe makes the business of designing a double-tuned filter quite straightforward.  The filter used in the original design of the DSB80 uses taps on the inductors for impedance matching into and out of the filter, while the circuit that the EMRFD software is based on uses a tap point at the connection of 2 series capacitors.  The filter I used keeps the output of the transmitter relatively constant over the 500KHz bandwidth of the US band:

Here’s what the board looked like with the mods finished.  The redesigned bandpass filter is at the left-hand side. Just to the right of it, the ferrite toroid wound with the green wire is the transformer that matches the low output impedance of the MOSFET final to the 50 ohms the bandpass filter needs to see. The VFO coil is on the far right of the board, just above the LM380.  The double-balanced mixer package (the heart of the rig) is the silver rectangular package just to the right of center:

Here you can see a closer view of the VFO toroid.  It’s not very easy to see, but very close to, and to the right of it is the 1N4001 diode that is used as a varactor to provide bandspread. The lead sticking out to the right is for the volume control and the lead leaving the board in the foreground is for the bandspread potentiometer:

Even though this particular board is 25 years old and has been worked over a few times by my soldering iron, I still think it’s pretty nice-looking:

I have only reproduced the schematics of the parts of the circuit that I altered. It didn’t seem appropriate to show the full schematic of the DSB80 here without permission. However, although the original article doesn’t seem to be available on the internet in good resolution, it is available from the right people if you know who to ask :-)

Now that the board was fully operational in both DSB and CW, the next task was to fashion a new enclosure.  I did want to retain some of the flavor of Richard’s version of this fine little rig and had wanted to keep the 2 small pieces of Meccano that he used in his tuning capacitor mounting bracket. After the decision was made to use an air-spaced variable instead of the polyvaricon that the original used, this didn’t seem possible.  I went with Richard’s suggestion to make a new enclosure from copper-clad laminate and use the original top-cover.

I cut 3 pieces of laminate for the bottom, back and front panels, and started marking the positions of the front-panel controls on a piece of paper.  When doing this, I mark the outline of the front panel life-size on a piece of paper and keep re-arranging the controls to find a suitable layout. This picture gives you the idea, though when this picture was taken, neither the paper layout nor the partially-drilled front panel were complete. To the right of the horizontal rectangular cutout for the frequency display are 4 holes that I drilled at what were to be the 4 corners of the vertical rectangular cutout for the modulation meter.  When making square or rectangular cut-outs, I drill a series of overlapping holes around the perimeter of the rectangle, remove the center piece, and use a small file to file the edges of the cutout smooth.  It’s slow work, but with care you can make some very acceptable cutouts:

Wherever possible, I mark the cutouts and hole-centers on the copper side of the board:

The finished front panel (before I realized I was going to have to enlarge the hole for the main tuning capacitor) -

The finished 3 panels with all cutouts and holes.  I think I might have cleaned and lacquered the boards at this point.  I scrub the boards clean with a Scotch-Brite pad, a little dish soap (washing up liquid for the Brits!) and plenty of elbow grease. This was the first time I decided to drill extra holes for those little “spigots” that help to keep switches and pots from rotating off-center -

 I use a hand punch to make holes wherever possible. It’s quicker and more convenient than drilling.  For larger holes, I start with a hole made with the punch, then enlarge it with a T-handled reaming tool. I got lucky and bought my punch from Harbor Freight for around $20.  They don’t carry this anymore, but similar punches are available online.  Mine came with a series of different-sized dies and looks like this:

I think it turned out pretty well:

Aw heck – I’m just dying to show you how the rig looks in it’s new case with it’s fancy digital display from N3ZI. The 2 knobs on the upper left hand side are the volume and bandspread respectively. Under the bandspread knob is a switch that will be used to switch between 2 different bandwidths when I fit a single-stage audio filter in between the AF pre-amp and the LM380 output stage. Under that switch is the headphone/speaker socket.  I did buy a nice speaker and grill cloth from Elecraft (a K2 replacement speaker) to fit in the top cover, but realized that drilling holes in the top cover might possibly damage the crinkle finish.  I didn’t want to risk that, so will probably live without an internal speaker.  I could always make a top cover from copper-clad laminate and drill holes in that for a speaker, but I like using the original top cover. Underneath the right-hand side of the frequency display is a toggle to switch the LCD backlighting on or off.  The meter is for monitoring modulation level in DSB transmit. The bank of switches on the far right are (top to bottom) TX/RX, DSB/CW and the on-off switch for the whole rig -

You’ll notice that I’ve used a hot glue gun to secure the VFO toroid to the board. This is also the first view of the 365pF air-spaced variable cap from Midnight Science. -

A few more views -

There are a few small issues that I’m working on. The TX does chirp a bit on CW transmit.  It didn’t do that on the bench, and I know that Richard’s version didn’t either. I’m pretty sure that a few more well-placed  RF bypass caps and/or feritte beads will cure the problem.  I think that I need to do a bit more work on how the board is grounded also.  Future projects will be to add a switchable bandwidth audio filter.  The later version of the DSB80, called the DSB2, had one, and I plan to use the same circuit.  It uses a single op-amp.  Richard’s version had a sidetone oscillator for CW and I’d definitely like to add one.  My antenna is rather inefficient on 80, so if I want much success on this band, CW will be the way to go.

Richard and I have kept up a regular e-mail correspondence in the last couple of months and in one e-mail, he told me how his DSB80 started it’s life -

A bit of history for you:  the rig first squawked it’s mighty 2 watts in anger at 00h08 27 January 1986; signals received by G4BMR Derek (599 about 40 miles away from my then QTH Swindon) but it wasn’t really the first proper QSO as I was already in QSO with Derek on 2M FM and had been for the previous 4 hours.  He was helping me to try and solve the hum, drift and chirp problems and we were also in QSO on 80M CW so all I did was just change rigs when I thought that I had the problems licked – it was quite a thrill to at last hear a nice clean CW signal coming back to me via 2M.  As soon as that had been achieved and we had swapped signal reports, Derek went QRT – not surprising after 4 hours!

I then finished boxing the little chap up but at 01h03 with the adrenalin still running high, there was only one thing for me to do and that was to call CQ.  I received an immediate response from OK3CSA Juro in Myto who gave me a 569 report;  for me, this has to be the first real QSO with the rig and also my first QRP QSO and my first QSO with something I had put together myself.  (Paper logs do still have their uses – the one in question is in front of me as I write – which is why I still to this day log this way!)

Here is that log entry of which Richard speaks – the QSO with Derek G4BMR and the first “proper” QSO, with OK3CSA -

Richard’s note continued -

Enjoy your time with your visitors and I look forward to reading the next instalment of the saga of ‘The little rig who found a new home in America…’

Well, the next installment begins here! The big success of this rig for me is that it has connected me to my ham radio past and filled in the gap on a long-lost piece of radio nostalgia.  It all happened because Richard G0BCT/F5VJD shared with me his first ever home-brew rig and allowed me to let loose on it with my soldering iron.

For that, I thank you OM!

Note – although the wiring on my version may look a bit neater, my version chirps and Richard’s didn’t.  He found that it was important to keep the various leads to the board well-separated, and I think I will end up bringing my connections out to the top of the board like he did in order to experiment with them to find a layout that works best.  He told me that his choice was between pretty yet defective, or scruffy and functional.  I am going to have to make the same decision the next time I take the top cover off this rig!

The intention when taking this photo was to set the DSB80 to 3985 – the North American QRP SSB calling frequency. It wasn’t until later I noticed that I had set it to 3895. These senior moments worry me!

PS – I liked Richard’s original version of this rig so much that I have kept the case, tuning mechanism and associated components intact in case I wish to recreate it one day.  I do like the ability to see where I am on the band with the LCD frequency display but in my opinion, his version of this DSB80 looked more like a “real home-brew rig”. I have not had a QSO with my version of the rig yet, but have spent many hours listening to it already. I love listening to this DC receiver! There is still a slight chirp for me to get rid of before I use it on CW and truth be told, I am more of a CW person than a phone person.  I was 100% phone in the earlier days of my ham career and maybe the pendulum will swing back in that direction one day but for some reason, after a working life in which I earned my living by talking (DJ’ing and voice-overs for radio and TV commercials), I now can’t think of very much to say on a microphone!  Even on CW, I tend to be more of a listener than “talker”, but I do love to listen. Besides – listening is the perfect thing to do while I’m building , and this little rig sounds great :-)

Stop Press – I fixed the chirp.  It was a wiring error on my part and a simple fix. Will explain in a future post. I also had my first QSO with the rig this evening (Oct 4th) on 75M DSB! More info to follow.

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