Dave Richards AA7EE

August 14, 2015

A Sproutie is Born in France, to Henri F6GMQ!

Filed under: Amateur Radio,Ham Radio — AA7EE @ 12:10 pm
Tags: , ,

Around the same time I heard from Andy M6YAO that he had finished his Sproutie, I heard from Henri F6GMQ, who was also building a Sproutie and close to completion. A Sproutie in Orsay, in the North of France – how inspiring! To my knowledge, there are now 3 Sprouties in existence – Henri and Andy came in joint second.

Henri built his regen in an old measuring instrument case. He kept the original 12V power supply, for powering the circuit. The variable capacitor came from an old tube radio. He’s already thinking of constructing a second one, in a nice wood or aluminum enclosure. Love those instrument handles!

A view from the back, showing the side braces that help to make the structure more solid. We must be thinking alike Henri, as my most recent version of The Sproutie also has instrument handles and side braces –

Henri’s first coil gives coverage from 5.5 – 7.2MHz. He says he has been able to listen to SSB, CW and broadcast stations and that selectivity and sensitivity are great, considering the relative simplicity of the circuit –

It’s interesting to see how other people build things. It looks as if Henri made his own Manhattan pads. Nice job! He also mentioned that he likes the AF stages of this receiver. Our thanks go to Charles Kitchin N1TEV for that, as they are the AF stages from the regen he described in the Feb 2010 issue of CQ magazine. Henri said that the receiver behaves exactly as I described. I do try to accurately reflect my experiences, so thank you for mentioning that Henri. I don’t think there’s any point in covering things up. If I think there’s a potential issue, I’ll mention it so you, the reader, will know what to expect.

Henri is looking for ideas for a simple 40M VFO, as 40M is his favorite band. He is thinking of building a high performance receiver for 40. If anyone has any ideas, you can leave comments underneath so that Henri will see them. He’ll be very grateful, and interested in all ideas, I’m sure.

Thank you very much for sending your photos Henri. It’s really great seeing how others build things, and it’s really great to know that there are now Sprouties in the US, the UK, and also France. Also, a big thank you to all who were involved in designing the circuit elements that make up this cool little receiver. They include (but are not limited to) GI3XZM, GM4HTU, G3RJT, G3VMU, G4RGN, VK2BHT, G3RJV, and N1TEV.

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August 8, 2015

Andy M6YAO Builds A Sproutie!

Andy and I have been communicating via e-mail since April. He is M6YAO now but back in April, he was plain old unlicensed Andy, who was about to apply for his Foundation License in the UK. He had built a Mark regen from Walford Electronics, which seems to have given him a taste for regens. He mentioned that it was a good receiver and worked well but that the tuning, accomplished by a polyvaricon with no reduction drive, was a bit critical, so he was looking for a regen to build that represented “the next step”, so to speak. It turned out that The Sproutie was that next regen for him.

I haven’t built any of the currently available regen kits but The Mark from Walford Electronics, and The Scout from QRPKits both strike me as good ones for anyone who has never built a regen, and wants to get their feet wet. However, when you’re ready for more, there’s nothing like a quality air-spaced variable capacitor and a nice solid reduction drive with calibrated dial to make you feel like you’re navigating the airwaves in style. In my secret (and perfect) world, there is a kit version of a regen with a pre-drilled and engraved, large and stout aluminum chassis, top quality air-spaced variable capacitors and reduction drives, and a variety of accessories (wooden enclosure, extra formers for adding bands, etc). Also, in my perfect world, this kit wouldn’t cost the many hundreds of dollars it would need to in the real world we all live in. If anyone were admirably eccentric enough to produce such a kit, I think that very few would actually buy it, due to the high cost.

Andy and I continued to e-mail each other, as his Sproutie gradually took shape. It was really interesting viewing the progression of his project as he encountered challenges, experienced setbacks, asked questions and one by one, solved his problems. It was a process that all home-brewers will recognize from their own pursuits, and a pleasure to observe. We have all had the kind of projects that present issues we are unable (or unwilling) to solve, so it is a fantastic feeling of achievement when projects succeed despite the obstacles that occur along the way. I get as much of a kick out of others’ successes as from my own – especially when it’s with a receiver like The Sproutie that is rather dear to me.

Incidentally, in the UK, when upgrading from a Foundation to an Intermediate license, there is a practical element to the requirements. Andy wanted to use his build of The Sproutie to qualify. The RSGB website says, “First, a practical skills assessment is taken which demonstrates your competence in basic electronics. This involves soldering a rudimentary circuit together using some of the components you learned about on the course.” A successful Sproutie build would seem to more than fulfill these requirements.

Bit by bit, Andy sourced the parts from various sources, including some from the US. He ended up with more reduction drives than he needed, and had to decide which one to use. He also incorporated a DC ripple filter from VE7BPO’s blog (I’m not sure if that became part of his final build). As the receiver slowly began to take shape, he was still deciding what to use for an enclosure. Whenever we build something, we make multiple decisions along the way, and it was interesting to follow along as Andy went through this process. I’m not sure if he experienced this, but I sometimes find that the plethora of decisions to be made really slows me down. Planning a project is a bit like playing a game of chess, as a decision you make now will affect many other moves in the future.

Although the AF amp board worked, on connecting all the boards together for the first power-up of the complete receiver, Andy was greeted by – a big nothing. We’ve all been through that and it can be somewhat dispiriting, but this is where our valiant builder’s homebrew mojo really kicked in, and he earned his stripes. He checked a lot of things, which all seemed to be in order, but didn’t give up. Finally, one afternoon, I received an e-mail that was titled “Eureka moment”. It turned out that his RF board was connected to the +ve supply line, but not to the ground. This is one of those “How on earth did I miss that?” moments that anyone who has ever built anything will know all about. Andy did experience a few more issues as he cased the set up but as they arose, he dealt with them. He said, ” I have learnt lots and I think it will help me in other projects I undertake in the future. ”

He used a metal file case for an enclosure, and the main tuning dial and drive is a NOS (New Old Stock) Muirhead Type C, with a 50:1 reduction ratio. 50:1 is huge – you must have fantastic slow tuning Andy –

Andy reports that it works well, fills the room with sound, and the bass boost works too. Because the file cabinet has a lid with a latch, he stores the unused coils inside the lid, held by spring tool clips. The plate on the top will have a legend, indicating the frequency ranges that the various coils cover –

Andy also owned a Tecsun PL-880 but he says that compared to The Sproutie, it seemed sterile. He writes, “The Sproutie seems to live and breathe in comparison and requires user interaction instead of just punching in a number through a keypad. ” He recently sold the Tecsun because, in his opinion, although it was probably technically better, it didn’t provide the same user experience as his new regen. A convert! This is exactly how I feel about direct conversion receivers and (particularly) regens. The simple circuit architecture leads to a relatively unprocessed sound and makes me feel as if I’m in more direct contact with the airwaves (or perhaps it’s just the lack of AGC!) It’s very affirming to hear the same sentiment voiced by someone who is a relative newcomer to these intriguing receivers.

Andy will be taking the exam in October to upgrade from his Foundation license to an Intermediate license. He already submitted his Sproutie build as the “simple” radio project part of his exam and of course, it passed.

Congratulations Andy, and thank you for sharing your Sproutie build with us!

April 3, 2015

An Early Morning Spin On 49M With The Sproutie

This morning, my 2 eldest kitties did a real number on me. The senior was the first. At about 5am, she sat on her food shelf (one of 3 shelves mounted on the wall next to my bed, specifically for the cats to hang out on), next to her empty food bowl and began meowing loudly, while fixing me with an innocent gaze. I was able to ignore this for a good 20 minutes until the next eldest, my blind cat Jingles, jumped up on the bed and also began a “feed me” campaign, which consisted of vigorously rubbing her little furry head against my face. The combined effect of both initiatives was too much to easily ignore so as soon as I had fed them, I found myself sitting in front of The Sproutie and thinking that I might as well make use of the fact that I was up at 5:30am, while night-time and grey-line propagation on 49M would be in full swing.

The choice of 49M for this listening session was simply because it was the coil that was plugged in. I listen to Radio Habana Cuba most nights on 6165 and 6100KHz. The 6165KHz signal, which comes online at 6pm local (0100z) has been rather weak recently, but the signal on 6100KHz from 10pm-midnite (0500-0700z) is a powerhouse. I sometimes record the 6100KHz signal but am quite often foiled in my attempts to catch the penultimate hour of programming, due to RHC’s various foibles. Last night, the carrier appeared on 6100KHz at 4 mins after the hour, followed a further 5 mins later by the audio. My plans to record the 1-hour program in English were thus foiled and by the time it was repeated at 11pm local, I was feeling too sleepy to last the whole hour.

When going to bed, I usually leave The Sproutie on 6100KHz so that I can awake to the sounds of KCBS Pyongyang on the same frequency. It is mainly music, with occasional spoken word in Korean. I hear many of the same tunes during their morning programming, and there is great theater of the mind in hearing their slightly kitschy melodies interspersed with the impassioned-sounding commentary in Korean. I hear the same melodies most mornings, and there is a certain appeal to this somewhat exotic “sameness”. I can imagine the members of the elite in Pyongyang waking up to this kind of “inspirational” programming every morning.

Coffee at the ready, I decided to perform a band scan on 49M with The Sproutie. The idea was to log every station I could hear on the band. The excellent site short-wave.info made it possible to quickly ID most stations, before moving on to the next. I didn’t linger for too long on any one frequency, as the goal was to get an overall idea of band activity, rather than to positively ID every single station heard.

Needless to say, I heard a lot of Chinese 🙂  Here’s what The Sproutie and I came up with –

 Freq  Station  Language  UTC
 5830  WTWW  English  1342
 5875  BBC  English  1343
 5915  CRI  Mongolian  1347
 5925  CNR 5  Chinese
 5935  PBS_Xizang  Chinese
 5955  CRI  English  1354
 5975  CNR 8  Korean  1356
 5990  PBS_Qinghai  Tibetan  1358
 6015  North_Korean_Jamming with un-ID’ed station underneath  1401
 6030  CNR 1  Chinese  1404
 6055  Radio Nikkei  Japanese  1405
 6065  CNR 2  Chinese  1406
 6080  CNR 1  Music  1414
 6095  KBS World Radio  English  1415
 6100  KCBS Pyongyang  Korean  1417
 6105  Radio Taiwan International (jammed, but jamming not heard)  Chinese  1418
 6110  PBS Xizang  Tibetan  1420
 6125  CNR 1  Chinese  1422
 6135  North Korean Jamming (w/ music underneath)  1424
 6155  CNR 2  Chinese  1427
 6175  CNR 1  Chinese  1429
 6185  Unidentified station (possibly China Huayi BC. Corp  Music  1431
 6190  PBS Xinjiang  Mongolian
 6195  BBC (jammed, but jamming not heard)  English  1434
 6200  PBS Xizang (or Voice Of Jinling)  Chinese  1436
 6250  North Korean Jamming  1438
 6280  Xi Wang Zhi Sheng (just 100 watts!)  Chinese  1440
 6348  North_Korean_Jamming_with_station_underneath_(presumably_Echo_Of_Hope)  1447

Lots of stations – and loud too, For the majority of the listening session, I had the RF gain on the little Sproutie cranked down to 1/2 or 1 on a 1-10 scale. Another benefit of this band-scan was that I got to fill in a few more calibration points on the dial calibration graph for this coil. The details on this screen grab are a little hard to read but that’s fine, as your calibration graph would be different anyway. Just take a gander at that nice smooth curve though –

Anyway, that’s it. It is now about 9:30am and I am beginning to wish I hadn’t risen so early. However, I blame the cats, and the good side is that I got to take a whirl on 49M before first light. Don’t let anyone tell you that you can’t use a regenerative receiver for serious SWL’ing. If anyone says that their regen doesn’t cut it for SWL’ing, just tell them that it must be because they didn’t build it properly 🙂

The Sproutie and a cuppa coffee kept me company early this morning throughout my sojourn on 49M.

February 26, 2015

A Popcorn QRP Regen Receiver and Lots More Air-Spaced Variable Capacitors

Many of us in the home-brewer community were really disappointed when Todd VE7BPO recently discontinued his popular and very through-provoking site “The QRP/SWL Homebuilder”. An archive of the site is available for download in pdf form and is a great resource. Though not quite the same as having the site, it’s great to have a copy of it for reference. Todd was having some issues with the site. He didn’t take it down due to lack of enthusiasm on his part and by way of proof, he’s back in style, with the new “Popcorn QRP – Scratch Homebrew Component-Level Radio Electronics” blog. It’s great – just like having his old site back. Todd combines circuit analysis and a theoretical approach with a strong leaning towards practical circuits that can be built by the home experimenter. Economy of design and performance are both considered, and from reading the accounts of Todd’s exploits, one suspects he is having a complete blast. If you haven’t visited Todd’s current blog or his previous site before, please note that the intent isn’t to provide the home-builder with complete step-by-step instructions on how to build a series of projects. This is circuit-level stuff, but if you’ve had a little experience at building circuits from schematics, all the circuits presented are tried and tested by our faithful protagonist, VE7BPO aka retired Professor Vasily Ivanenko.

All this is leading up to something, and that something is that our intrepid experimenter recently announced he had been revisiting the subject of regenerative receivers. He had built 4, and was sharing one of them with us on his blog. Happy, happy, joy, joy! Even better, this circuit was the same basic topology that I used in The Sproutie – a  circuit that separated the Q-multiplier and detector into separate stages. It’s an arrangement that is well-behaved and performs well. The regen control, a resisitive component, exhibits no hysteresis, and the addition of an RF preamp means that the circuit doesn’t suffer from common mode hum. If you build it well, it will be frequency-stable too, but that part is up to you 🙂

The blog-post is here. It is based on the regen circuit published by Makota 7N3WVM, whose website is a treasure trove of circuits for the home builder. You’ll notice great similarity to the circuit of Nicky’s TRF that first appeared in SPRAT Issue 70 in 1992, and N1BYT’s WBR from QST Aug 2001. What’s really interesting though, is that Mr Ivanenko has added a bipolar transistor (a 2N4401) to the J310 FET infinite impedance detector, to turn it into a hycas (hybrid cascode) pair in order to increase the level of audio from the detector, as well as the reverse isolation, which can never hurt, right? Great idea! His circuit includes a bipolar RF preamp in common base mode to add isolation of the oscillator from the antenna, as well as a little bit of gain, and a 2-transistor preamp after the detector that he has used in other “popcorn” designs. He also makes his argument for continued use of the LM386 as a final audio amp in this post. The description in the 2nd paragraph, of the folklore surrounding regens is mirth-inducing – and spot-on.

I know that at least a few builders are considering making their own Sproutie and if you are still at the planning stage, you might want to think about Todd’s version of the front end. I haven’t tried it (yet) but Todd ain’t no slouch 🙂  If I were to incorporate it into my next regen build, my current thinking is to use his front end, and feed it into a one-stage active audio filter using a 5532 op-amp or similar, and then into a nice, low-noise LM380 with it’s fixed amount of 34dB gain. If I ever do this, I can promise you two things –

a) it will be many months, maybe even a year before I do it, because I am very slow at these things and

b) I’ll show you the circuit of my AF stages so you can join it up with Todd’s (ahem, I mean Vasily Ivanenko’s) front end circuit

 

Todd just revealed 2 encouraging pieces of news –

a) He just ordered some black and red chicken-head knobs for his next project and

b) He has decided to spend another 2 weeks working on regens

If you don’t already follow Popcorn QRP, it’s well worth adding to your RSS reader, bookmarks bar or similar.

 

The rest of this post may be a little annoying to those who have limited bandwidth connections, though I imagine anyone who is still surfing the internet on a dial-up connection or a very slow mobile connection learned long ago not to come here 🙂 I recently acquired some more air-spaced variable capacitors and I’d like to share some photos of them with you for no other reason than short-term visual gratification! As always, my preferred brand is Hammarlund. Not only are they of high quality, but I happen to like the way they look as well. They are drop-dead gorgeous.

I’ll start with a piece that was acquired a few months earlier, before the current flurry of buying activity. This is an MCD-50-M and may well end up as the main tuning capacitor of my next regen, unless I happen to find another MCD-35-MX like the one that was used for tuning The Sproutie. MCD means that is is a double-ganged unit (unlike the single-ganged MC units), 50 is the maximum capacity of each section, and the M at the end refers to the fact that the offset rotor plates give it a “midline” capacity characteristic, keeping the rotation vs frequency characteristic reasonably linear. Nickel-plated brass vanes for a good temperature coefficient, and all mounted on a high-Q ceramic base. Perfection! Look at those bright and shining never-been-soldered-to-before terminals –

Leaping forward in time to a couple of weeks ago, this MC-200-M “midget condenser” came into my life sporting an older original box, in almost as good condition as the capacitor itself. I love the graphic design on these older boxes –

Then came my haul of just a few days ago. I bought them all from the same seller. The boxes are a bit beaten up, but the capacitors are in great condition. First off, here’s the group shot-

Among them were two of these HFA-100-A’s. If you’re as picky as I am, these are not ideal for maximum stability in a VFO or receiver tuning control, as the vanes are only supported at one end. It would be fine as an antenna trimmer where it’s placed in series with the antenna lead, or as a reaction control, in a regen where a variable capacitor is used for this function. I’m not sure what material the vanes are made of in these parts –

In the same vein (vane?), I also scored an HF140. What a great part. It offers two methods of mounting. If I possibly could, I’d use both of them for maximum stability. This variable cap could be mounted underneath a chassis so that the nut on the threaded shaft helps to hold the front panel to the chassis, while the mounting bracket was screwed to the underside of the main chassis for extra rigidity. Rigidity is a very good thing with regens 🙂 –

An MCD-100-M (2 x 100pF).  Nickel-plated brass vanes, a ceramic base (steatite actually), regular plate-spacing, and a “midline” capacity characteristic . Such a beautiful part. What else can I say? The US was once a manufacturing powerhouse –

Also in the haul were 3 x MC-20-S. I used one of these (from another buy) as the fine tuning control in The Sproutie –

Lastly, here’s an MC-50-MX. Single gang with capacitance swing of 10.5 – 53pF, midline capacity characteristic (for reasonably linear rotation-frequency relationship) and extra-wide plate spacing. This would be great for a VFO –

 

I also very recently acquired this National gear drive with 3 x 250pF variable capacitor attached. My relative lack of knowledge on National products caused me to misjudge. I discovered when it arrived, that the gearbox is a later model that is smaller than the older “classic” National gearbox drives. Also, it doesn’t have an eccentric bushing for driving the micrometer-style dial. I read somewhere that National stopped using the classic dial in their receivers in response to upgraded mil-specs that negated it’s use. It’s in good condition and turns freely, though the grease is old and it would probably benefit from a cleaning and re-greasing. I may well put this one up for sale –

There’s a little bit of surface dust on the plates and shaft but otherwise, it’s clean, and those terminals have never been soldered to. Amazing! –

No cracks in the insulators –

There’s only one detail that would require some attention from a builder, and that is that it looks as if the underside received a thwack at some point – either that, or it’s a manufacturing defect. One of the mounting holes is distorted and would need re-drilling and re-tapping if it is to be used. I think this is a solvable issue –

Another view showing this issue –

Old grease on the gears. If I were to use this, I’d want to clean out and re-lubricate, but that’s par for the course with these old yet still very serviceable gearboxes –

 

That’s it for now. Hope you didn’t mind me sharing all these pictures with you. As a parting thought, if you’re still planning to construct a regen and haven’t completely decided what to build, remember to take a look at VE7BPO’s Regen #4.

 

 

February 17, 2015

Extra Coils For The Sproutie Regen, With Coverage Up To 30MHz

Filed under: Amateur Radio,Broadcast Radio,Ham Radio,QRP — AA7EE @ 3:43 am
Tags: ,

Since completing The Sproutie Regen in it’s basic form in August of last year, I have been spending lots of time listening to it, and also some time winding coils for extra bands. On top of that, I wanted to add some extra thoughts and observations on building it and instead of creating a new blog-post every time I wound a new coil, or found something new (such as the fact that it seems to work quite well all the way up to 30MHz), I have chosen to add to the original blog-post. I have also been editing the post a little while adding new material, the point being to improve it and make it as informative as possible to anyone thinking of building it. Also, if I added a new blog-post for every new piece of information, then potential builders would find it harder to access all the info. This way, if you want to learn about, and maybe build The Sproutie, reading the one original post will always bring you up to date.

Since finishing The Sproutie, I have added coils for 2063 – 2670KHz, which covers the 120M BC band, 49M, 31M, 25M, 19M, 16M BC/17M ham, and an experimental coil that covers ~24-29MHz. The coil box is now full, and a picture of it has been added to the original post. I have also updated the coil tables to include full details. The experimental coil for 24-29MHz was wound out of interest, to see if this receiver would work passably at the higher HF frequencies and indeed, it does seem to. I copied SSB on 24M, as well as SSB  and CW on 10M, and local CB’ers on 27MHz. (EDIT on 2/18/2015 – this afternoon, I copied 10M beacons from K5AB in Texas on 28280KHz and WA2DVU in NJ on 28257KHz) I added no padders or series caps to taylor the coverage to a specific band. I didn’t even add a link winding – plenty of RF was being coupled into the circuit from pin 7 of the octal base without it, though a finalized coil would probably include a small loop to couple as much RF as possible, withut overloading the detector or stopping the oscillator.

Blog posts aren’t much fun without photos so, although I just added this photo to the original post, here’s what my coil box looks like now that it’s full up with coils.  If I wanted to add coils for specific ham bands, as well as the remaining BC bands above 16M (and the 22M band), I daresay I could fill another coil box!

The cigar box full of Sproutie coils. The unmarked one sitting above the 25M coil is experimental, and covers approx 24-29MHz.

If you’re getting a bit fed-up with me talking about this little receiver a full 6 months after I finished building it, take it as evidence that it’s a good ‘un. 6 months after building it, I still think that it was a very worthwhile project, and continue to derive much enjoyment from it.  The sounds of Radio Habana, Cuba fill my apartment on many evenings, and on the same frequency (6100KHz), music from KCBS Pyongyang in the mornings, as well as Radio Australia are my main morning staples. I’ve heard Spanish numbers stations, air-traffic control, coastal stations, military communications, and all sorts of weird and wonderful bleeps and bloops that you expect to hear in the shortwave bands. Before I end this post, allow me to say just one more thing that I have said many, many times before. If you are going to build a regen, make sure you pay careful attention to the physical construction. There, I said it. I promise I won’t mention it again 🙂

 

January 27, 2015

Aaron N9SKN’s Sproutie Regen Receiver

I was quite excited when Aaron N9SKN told me he was building a Sproutie. Sometime earlier, I had discovered his website, billed as the “Home Of The 500mA Sidetone Oscillator/Shack Heater” I was searching for information on building HF receivers, and came across Aaron’s build of W7ZOI and K5IRK’s Progressive Receiver, as described in the Nov 1981 issue of QST, and the ARRL handbook for several years. Look at the pictures of the boards that Aaron made for the project in this article. Good stuff!

Aaron’s Sproutie build must have been a breeze for him in comparison. What a beaut. I’m wondering what material he made the front panel from. Is that garolite or something similar, or is it foam-core board? He did a great job of cutting the oval hole for the speaker. I like the “oxblood” color of the phenolic tube bases too – the same color as the Doc Marten’s I wore as a young man 🙂

 

“The Sproutie” as built by Aaron N9SKN. Photo courtesy of N9SKN

Aaron already had a Cardwell 2 x 35pF tuning capacitor in his “junk” box. It was still unused, which is why I put quote marks around the word “junk”. I am often amazed at the number of these lovely old vintage parts that have yet to be used in a project – it’s a great thing for us home-brewers. You can see it in this rear view of the receiver. Note the aluminum plate he installed behind the front panel to minimize hand capacitance effects. I’m looking at those leads from the tube base and the variable capacitors to the circuit board, and wondering if he gets any microphony effects –

Rear view of N9SKN’s “Sproutie”. Photo courtesy of N9SKN

A view of the underside, showing that oval speaker –

The underside of N9SKN’s “Sproutie”. Photo courtesy of N9SKN

Aaron is a hardier soul than me, as he made his own Manhattan pads. Here’s a view of his RF board –

The RF board in N9SKN’s “Sproutie”. Photo courtesy of N9SKN

Nice job Aaron. He posted 5 videos of his Sproutie in action too. Here’s one of them, showing his Sproutie in action on the 25M band. You can find the other videos of his Sproutie on his YouTube channel –

One of the enjoyable things about sharing pictures and descriptions of my activities in this blog, is hearing from builders like N9SKN. It’s great to know there are other people out there building things. I am occasionally tempted to spend my money on a commercially-made HF receiver instead, but I wouldn’t have anywhere near as much fun. Thanks very much for sharing details of your Sproutie build Aaron!

PS – Allow me to rave about Aaron one more time. He scratch-built a K8IQY 2N2/20 Manhattan-style. Major respect!

January 7, 2015

Does The Sproutie Regen “Work” On SSB and CW?

Since building The Sproutie a few months ago I have had a great deal of fun with it. It is only the 4th regen I have ever built, but it is the best one so far. One of my main motivations for building it was to own a “serious” regen. I have long thought that the main reason this type of receiver is not taken more seriously nowadays is because they are rarely taken seriously when being built – and perhaps even designed. Kit designers are forced to make severe compromises because, well, who is going to pay hundreds of dollars for a high quality regen kit? A few of us would, but probably not in large enough numbers to make such a kit economically viable.

As an example of taking things seriously when building a regen, take a look at this build of NR5Q’s “Ultimate Regen” by Jim K4XAF.  Now that is a receiver any avid SWL would be proud to own and operate.

To make a long story short, I wanted to prove to myself that a regen could serve as a useful and valuable listening tool.  I was mainly concerned with SW AM broadcast stations as my main station rig, a K2, doesn’t have general coverage receive. For AM shortwave listening, The Sproutie is indeed very usable, and definitely more than just a novelty. I had spent very little time or effort listening to SSB and CW, and my initial impressions were that CW reception was fine, but SSB reception was occasionally good and occasionally not. I didn’t really think about why, and thought that perhaps it was something to do with the design that I didn’t understand.

Recently, I spent some time with The Sproutie on the ham bands, and the obvious finally occurred to me. It works fine on SSB but when the input signal is too strong, the oscillator pulls, resulting in FM’ing of the signal. In order to overcome this, the best way to operate The Sproutie when listening to SSB is to run the AF gain at, or near, maximum volume, and use the RF gain to set the desired volume. This will ensure that on strong signals, the RF gain is kept down. This is counter-intuitive to anyone who is used to operating a modern receiver with a product detector, where the modus operandi is usually to keep the RF gain at, or close to max, while using the AF gain to control the volume. However, if you got your start with SSB by using an older receiver that had a diode detector and was primarily designed for AM, you’ll remember that controlling the amount of BFO injection was fairly important in resolving the SSB signals well. With one of my first radios, a British R-107 WW2-era military receiver, I was taught to keep the AF gain turned up, and to control the signal-to-BFO ratio by adjusting the RF gain. On strong signals, I quickly learned to keep the RF gain down so there wasn’t too much input signal for the amount of BFO signal. With The Sproutie, the principle is the same, except you are also limiting the amount of input signal so as to not cause the oscillator to pull. Those who have built and operated a number of different regens will be able to comment on this, but my sense is that this is a very common issue with them. Perhaps some designs minimize the effect of oscillator pulling. Can anyone more experienced than me comment? (Note – qrpgaiijin did. Please see his comments below this post on the reasons for oscillator pulling in regens. Input from experienced builders is very valuable so if you’re interested, please do take the time to read.)

Also note that another technique you can use to prevent oscillator pulling on stronger signals is to increase the amount of regeneration. On weaker signals, you might want to reduce the amount of regeneration closer to the “critical” point of onset of oscillation.  At that point, sensitivity is greater, which will help with the weaker signals. Of course, all these adjustments will affect the tuning, so you will need to adjust for that. It’s all part of the fun of operating a regen!

To sum up, The Sproutie does indeed resolve SSB signals well, but it requires much more attention and input from the user than other receiver architectures do. The “sports car with a stick shift” analogy works well here. When tuning the bands for SSB signals, you need your hands on the controls on a much more regular basis than when tuning AM signals. Listening to a QSO with stations of vastly different signal strengths can be an exercise in user attentivity and engagement.

By contrast, listening to AM stations on this receiver is much easier. If the oscillator pulls a few 10’s of Hz on strong AM signals (which it almost certainly does), you’re not going to hear the effects. It’s still a good idea to run the AF at a high gain setting so as not to overload the detector, but the need for this is nowhere near as critical. In fact, listening to AM stations on this little gem isn’t much more work than doing the same thing on a superhet. Although the precise regeneration point varies with frequency, you don’t need absolute maximum sensitivity when scanning the band for signals. When casually tuning a SW BC band, I can tune several hundred KHz before roughly resetting the regeneration control. Only when I find a signal I want to investigate further do I take the time to set the regeneration more precisely.  It’s a process that becomes second nature after a while. I can almost imagine the diehard regen users in the 1930’s deriding owners of the newer superhets, as they were too easy to use and “not real radios”. What’s the betting that happened?

So here’s the deal – The Sproutie does indeed receive SSB just fine, but you’re going to have to put a bit of work into it. It is, after all, a sports car with a stick shift, and not a luxury sedan with an automatic transmission:-)

NOTE – I just read the original article in Electric Radio magazine, describing NR5Q’s “Ultimate Regen”. There is, of course, no definitive word on whether it is indeed the best regen out there, but I took heart from the following quote by Bruce,

“Before we go any further, if you are a SSB operator you may be wasting valuable time. While I listen to SSB all the time on my ‘regens’ I would not want to try to operate a SSB station using nothing but a homebrew regenerative radio – that would be an exercise in futility.”

The above quote comes from a gentleman who built over 60 regens and authored many articles in the pages of Electric Radio. His words mirror my experience with The Sproutie, and further cements my belief that, as far as regens go, this one is pretty darned good. I love listening to AM on it, really like listening to CW on it, and although I can listen to SSB on it with little difficulty, I’d rather listen to SSB on a superhet with a product detector.

Apologies if you’re viewing this on a low-resolution screen, but I have an affinity for nice large pictures of radio sets.

November 23, 2014

Videos Of The Sproutie Regen In Action

Many apologies for taking so long to get these videos up. The only camera I have that can do video is so old and gives such poor quality video, that it’s a little tough for me to feel inspired in that direction.  I do like to put quality still pictures on my blog, and am currently unable to do justice to my projects when it comes to videos.  However, even a low-res video can still give you an idea of how a receiver handles that no amount of still pictures can, so last night and this morning, I made a few brief videos, and here they are. I would recommend viewing them on this page rather than on YouTube, simply because there is no point in seeing the larger version on YouTube – the video resolution simply isn’t there. Aaron N9SKN is building a Sproutie, and asked if and when I was going to post videos. His request gave me the final push/feeling of guilt that was needed to get me moving!

Here’s The Sproutie receiving CW and SSB on 20M (with the coil that tunes from 12100 – 14400KHz) –

and here it is receiving AM stations on the 60M and 49M BC bands (with the coil that tunes from 4810KHz – 6320Khz) –

As the main blog-post on The Sproutie shows, I have coils for continuous coverage from about 3MHz up to 16MHz (as well as a coil for 2.1 – 2.7 MHz) and have wound temporary coils that worked up to 24MHz. It will probably work even higher. I have even read reports of Nicky’s TRF (which is the circuit I used for The Sproutie’s front end) being used successfully on the 10M amateur band!

The original blog-post giving construction details of The Sproutie is here.

August 21, 2014

The Sproutie – A General Coverage Regen Receiver with Plug-In Coils

NOTE – Many thanks to Aaron N9SKN and Cliff WA9YXG, who pointed out errors in the schematics. They have been corrected, and N9SKN has built a working Sproutie from the schematics in this post so rest assured that if you follow them, you can too.

If you’re thinking about building this great little general coverage regen, I’d urge you not to print out any of this article to work from. The reason is that whenever I make an improvement or addition to this receiver, I edit this article. By working from a printout, you’ll be missing out on any changes I subsequently make. Having said that, The Sproutie works fine as is, so don’t be scared off from building it.

I’ve mentioned before in posts how one of my first shortwave receivers as a teenager growing up in England (in fact, possibly the first) was a one tube battery-operated regen built from a kit. Many of the popular electronics magazines at the time, including my favorite, Practical Wireless, carried advertisements from a company called H.A.C. (“Hear All Continents”) who sold kits for simple HF regenerative receivers. This was the ad I remember best. To the teenage me, this receiver was the holy grail. With this receiver, there would be no stopping me. I would be the king of the hill, if only I could have this magnificent shortwave receiver –

Ads like this for H.A.C. shortwave receiver kits were common in the UK up until the early 1980’s. Image taken, with permission, from Louis Meulstee at http://www.wftw.nl/

I saved my pennies and eventually sent off for the H.A.C. Model DX Mk. 2. It wasn’t as fancy-looking as the one picitured in the ad, as it didn’t have a front panel or a calibrated dial but hey – those kinds of regens were only for the truly well-heeled, and I was just a kid with a modest allowance. The kit that arrived used an HL23DD valve (or equivalent). It was a battery operated double diode triode, with a coated filament, to maximize emission on the low filament voltage of just 1.5V (2V maximum, with a current consumption of just 50mA). This set didn’t have a front panel or a calibrated dial, sporting just a modestly-sized aluminum chassis with 3 chicken head knobs on the front, but with my 2000 ohm headset and 90V high tension battery, I truly was the king of the shortwave hill. I don’t have any pictures of my H.A.C. Model DX Mk. 2, but featured here are pictures of someone else’s taken from Louis Muelstee’s great website, which is where the ad shown above came from too.

The H.A.C. Model DX Mk. 2 cost me all of £14.50 in the late 70’s. (Photo taken by Philip McNamara and taken, with permission from Louis Meulstee at http://www.wftw.nl/)

This one tube regen used an HL23D double diode triode tube with low current consumption 1.5V filament. The blue lead on the left leads to a connector that plugged into a 90V high tension battery. (Photo taken by Philip McNamara and taken, with permission from Louis Meulstee at http://www.wftw.nl/)

Truth be told, this wasn’t exactly the most sensitive receiver ever created, but it mattered little to a teenager in England in the 1970’s, with plenty of loud shortwave broadcast signals. There was much to keep those high impedance headphones firmly glued to my head. They were fairly cheap quality, and the way the metal headband tensioned the earpieces against my ears made them a little red after 30 minutes of use. Did I care? Not at all – I wore them for hours on end, as I was enthralled by the sounds of Radio Nederland, Radio Prague, Radio Tirana Albania, Radio Moscow, The BBC World Service and many other broadcasters, as well as all the weird-sounding utility stations and the very mysterious numbers station from East Germany. I had no idea back then what it was, but the female voice announcing strings of numbers in German was strangely compelling. Every day, I would rush home from school, eager to get into my bedroom, plug the low-tension battery in, wait for a short while for the tube filament to heat up, then connect the high tension battery and clamp the headphones to my head, cup of tea by my side, as another listening session began. Weekends were heaven. As soon as all my homework was out of the way, there was nothing but blissful hours and hours of potential shortwave listening time stretching ahead. From time to time, the 90V battery would run down, and I would walk the 2 miles into the village of Astwood Bank to buy a new one from the local gas station.  It didn’t take me long to figure out how to power the filament from a transformer in order to save money on low tension batteries. I eventually figured out how to do the same for the high tension supply too. On good days, I could even pick up some local amateurs on 80M SSB. Man, I was indeed the king of the shortwave hill! At the back of my mind, though, was the idea that somewhere out there was still a truly dreamy shortwave receiver – one that had a front panel fashioned from a sheet of aluminum, and a calibrated tuning dial. It only took me until the age of 50 to finally own one of those only-in-your-dreams kind of receivers.

Which is what this blog-post is all about.

I’ve had some encouraging success with regens recently. Both the WBR and my modified version of the the WBR, which I built for the 31M BC band, worked well, with no common-mode hum, instability, or any of the other kinds of naughtiness that sometimes accompany the operation of regenerative receivers. There was one main thing about the WBR’s that limited them for me, and that was the fact that they only operated on a limited range of frequencies. After building these 2 receivers, the next logical step was to build a general coverage regen with plug-in coils. I wanted a set that was built solidly, with a reduction drive and a calibrated tuning scale, so that I could prove to myself something that I already knew – that a regen, properly constructed, can serve well as a shortwave receiver rather than just as a novelty, which seems to be the category most people have placed them into these days. I’m reminded of a comment on a discussion forum I saw recently, in which a gentleman was talking about a regen he had built once. It was sensitive, received lots of stations, and gave him much enjoyment, he said, but he never really knew where he was on the band. “Well of course you didn’t!” I thought to myself, “but that’s not because it’s a regen – its because when you built it, you didn’t build it with a calibrated dial. It’s not the regen’s fault you didn’t know where you were on the band – it’s yours!”

Charles Kitchin had a design for a receiver which caught my attention. It was published in the Feb 2010 edition of CQ Magazine and consisted of an oscillating detector feeding a 2-stage amplifier consisting of a low-noise FET-input opamp acting as the preamp. The preamp had a low-pass filter with a variable cut-off point, as well as an extra capacitor in the audio chain that could be switched in to give a nice lift to the lower frequencies, for those times when you have a nice strong signal and want a bit of bass boost. This preamp drives an LM380, which makes for a much lower noise AF amp chain than the default in these types of receivers that employ an LM386. On top of that, there is provision for a line out jack for recording. I was interested – regardless of the front end I used, this could definitely be the AF amp for a “serious” regen!

Before I had even fully decided on the finer details of this project, I assembled the AF amp on a separate board. I wanted this to be a somewhat modular receiver, with the AF and RF sections built on different boards so that if either section didn’t work out, I could try a different one. I wasn’t entirely convinced that the value of Hammarlund tuning capacitor that I was planning on using was going to be ideal, so I wanted it to be a relatively easily swappable part with other tuning capacitors of different value but with the same form factor (of which I own a few). If I was going to go to the trouble of building something like this on a nice chassis, I wanted to give myself the maximum possible chance of succeeding.

Here is the schematic of the AF board. It is a little different from the version originally designed by Mr Kitchin (though not by much) as I will explain –

In Chuck’s original version, the 2.2K resistor on the input was 5K.  The ratio of this value to the value of the 100K resistor between pins 2 and 6 of the AD820AN determine the gain of the stage, and I wanted a bit more. Also, the LM380 was motorboating when the AF gain pot was set to anything higher than half-volume, so I added the 10 ohm resistor in the supply line and bypassed it with a 470uF electrolytic, which stabilized it nicely. The +ve supply line was connected directly to pin 7 of the AD820AN, but this could also be bypassed if necessary. A series 100 ohm resistor with a 47uF or 100uF bypassing to ground should work nicely. You can also sprinkle a few large decoupling electrolytics in the range of 100 – 470uF at various points on the 12V bus directly to ground. A small issue I experienced was that when the AF gain pot was at absolute maximum volume, rotating the low-pass filter pot caused clicks and “bloops” in the speaker. It seemed to only happen when the slider of the pot had finished traveling over the carbon track and had actually made contact with the metal that formed the hot end of the control. A 47 ohm resistor placed at the hot end of the 10K AF gain pot provided the necessary isolation (this is shown in the schematic), and I was left with a volume control that operated smoothly, and a variable low-pass filter pot that also operated smoothly. I also added a 0.1uF coupling capacitor on the input (pin 2) of the LM380. The 0.1 and 220uF bypass capacitors on the 12V line were placed so as to bypass the 12V supply directly at the point of entry into the chassis. They were soldered directly on the back of the DC power connector and grounded with a solder tag bolted to the chassis. The 1N4001 diode was also placed at the same point.

Here’s the AF board as I first built it, before changing the 5K resistor on the input to a 2.2K resistor – and before adding the 10 ohm resistor in the 12V supply line and the 470uF capacitor to bypass it. The lengths of lavalier mic cable for the variable low-pass filter and the AF gain potentiometers have already been soldered in place, and they exit through holes drilled in the board. The headphone jack and DC power connector are temporary, for the purpose of testing. The Manhattan pads are of course, as always, W1REX’s MeSQUARES and MePADS

The front end is a very standard design. It is the same configuration (and indeed the same circuit) as used in the WBR, with the exception that the tank (unlike that in the WBR) is unbalanced. This same arrangement was used in Nicky’s TRF, as featured in issue 70 of SPRAT, and I believe the original circuit was developed by GI3XZM. I wanted this receiver to be usable over a wide range of frequencies, and in keeping with my “modular” approach, wanted the receiver to be as versatile as possible. A plug-in coil system, with both gangs of a dual gang variable capacitor, as well as the fine tuning capacitor, all available at the pins of the coil base, allows for a lot of flexibility when winding coils for different bands. The user decides, when constructing a plug-in coil, whether to include parallel or series capacitors for the main tuning and fine tuning capacitors, as well as choosing whether to use one, or both gangs of the tuning capacitor. In this way, with some calculations and a bit of trial and error you could, say, wind a coil to cover a large segment of the HF spectrum, or a single narrow band of frequencies. If, after some listening, I decide one day that I am particularly interested in the 16M broadcast band, I can construct a coil to cover just that one band. Neat!

The J310’s in the RF amp and the detector stage could be any similar N-channel JFET such as the MPF102 or the 2N3819. Likewise, the two 2N3904’s could be most any small signal general purpose NPN transistor. I originally fed the output of the J310 “infinite impedance” detector stage directly into the input of the AF amp board, but quickly discovered that the gain wasn’t enough to comfortably drive a loudspeaker. Had I done a few quick calculations beforehand, I would have realized that. I wanted to take advantage of the fact that the output chip is an LM380, by driving it enough to make a loud noise into the speaker! Adding the single 2N3904 preamp stage after the detector solved the problem nicely. I have built enough of these simple receivers that can drive “a small speaker to a comfortable volume in a quiet room” 🙂 No more!

As with any circuit of this type, the RF stages, and the frequency-determining part of the circuit especially, should be built with short leads, and stiff wiring. Top quality components will help.  The two 330pF capacitors in the feedback circuit of the 2N3904 oscillator stage should be NPO’s (or C0G’s – same thing), as should the 39pF capacitor. The coils were wound on toroids, and the coil assemblies mounted in octal tube bases. I spent a great deal of time on W8DIZ’ site, using his online calculators to figure out the number of turns required for varying degrees of coverage. Unless you build a receiver with the same variable capacitors, and use a very similar physical layout, you’ll need to do your own calculations, and then be prepared to tweak the final values of inductance and capacitance to get the coverage you want. Incidentally, I used a Hammarlund MCD-35-MX dual gang component for the main tuning capacitor. It was this one that I got a deal on over a year ago. The official specs say that each section has a capacitance of 6 – 31pF, but I also had to make a rough estimate of the stray and circuit capacitance when calculating the required values of inductance and capacitance to cover each band. My fine tuning cap was a Hammarlund MC-20-S, and I had to include the capacitance of that in the calculations too. This is the online calculator on W8DIZ’s site for the T68-6 core. He has similar calculators for all the popular toroids. Very useful stuff.  Note – for some reason, the calculator doesn’t always estimate the correct length of wire that needs to be used. This is easy to work around. Just wind one turn around a toroid measure it’s length, multiply that by the number of turns, and add a few extra inches for good luck (and pigtails).

Here’s a view of the RF board as initially built, before adding the extra (pre-AF board) preamp stage –

Here are the details of the coils wound so far, including the temporary “experimental” coil for 24-29MHz. I didn’t get as far as installing a link winding for this coil, but the main coil was picking up plenty of signal from the proximity of pin 7 of the tube socket to the coil. I have been very pleasantly surprised at how sensitive and stable the set is at these higher frequencies. Soon after winding it, I copied SSB on the 12M and 10M amateur bands, as well as plenty of over-modulated and very loud local signals on 27MHz 🙂  Unless you also use the same values of tuning and fine-tuning variable capacitors, and closely copy my layout, your values will be different, but here is the info on my coil set so far. After a little while spent looking at it, it should make sense. Once you get used to figuring out how to wind a coil for a specific set of frequencies, it’s fun.  I have 15 coils so far, with ideas for a few more. I have already filled up my cigar box coil box, and am getting ready to make a second coil box and wind a few more coils. One of the really enjoyable things about a regen with plug-in coils is making coils for new bands. Fun!

If you wind too many turns for the link winding, you may find that you have to turn the regeneration control nearly all the way clockwise in order to reach oscillation, or you may not be able to reach it at all, as the link winding loads down the oscillator. It is particularly easy to do this on the higher frequency bands. If this occurs, remove a turn or two from the link winding. In operation, it is easy to overload the detector (as it is with all regenerative receivers). I use my Sproutie with a large outdoor antenna and find that on the lower bands, I usually only need to operate the set with the RF “gain” control set halfway.

The 15855 – 17850khZ coil stops about 50KHz short of the top of the 16M band, which is nominally 17480 – 17900KHz. However, all these coverage figures are quoted with the fine tuning control set to maximum capacitance. With the fine tuning control, I can tune all the way up to 17900KHz with that coil plugged in.

With the first set of coils I wound for specific bands, I was using significant values of fixed capacitance across L1 in order to reduce the frequency swing caused by adjustment of the main tuning capacitor. I noticed after a while that these specific band coils weren’t giving such good sensitivity as the general coverage coils. I have since discovered that it is best to avoid large values of parallel fixed capacitance, as this seems reduce the performance. Adding a capacitor of a few pF to tweak the coverage is fine, but large values (of the order of 50 or 100pF) will reduce performance. If you want to reduce the frequency swing to cover a narrow band, best to achieve it with the use of a capacitor in series with the main tuning capacitor instead. The performance of the coils in this receiver seems to be maximized by using as much inductance and as little capacitance as possible. This is more noticeable on the higher frequency bands.

The table for specific band coils is a work in progress. I will add to it as I wind more coils –

The coils were constructed in two different ways. The lower frequencies used a larger T68-6 core which I mounted with nylon hardware. I first took a #10 nylon bolt, cut the head off, and epoxied it into the hollow center spigot of the tube base thus –

Before adding the toroid, any jumpers and capacitors were soldered in place (this is going to be the 3050- 3950KHz coil). The soldering’s a bit messy, but it was the first time I had soldered one of these things –

A couple of nylon nuts followed, then a nylon washer, and then the toroid, topped off by another washer and finally, another nut –

The higher frequency coils used T50-7 toroids, and were mounted vertically and secured with a couple of dollops of hot glue from a glue gun. In the following picture, the 3050 – 3950KHz coil is on the left, the 14460 – 15980KHz coil in the middle (in a white ceramic tube base), and the 8040 – 10720KHz coil on the right.  The middle and right coil were pictured before the hot glue was added. Since building this version of The Sproutie, I have started using hot glue for the larger, lower frequency coils too, and it works fine. It is a lot faster than using the nylon bolts and nuts –

Here’s the 14460 – 15980KHz coil with the 2 dollops of hot glue to secure the toroid. I like these ceramic bases and think I’ll use them for all subsequent coils. Incidentally, here’s a quick hot glue tip. I don’t know what temperature the guns that have a single setting use, but if you purchase a dual-temperature gun and use the dual temperature sticks, the hotter setting allows the the glue to flow more freely before it sets, which makes building these coils a bit easier, and gives a better end result. I think the coils in these photographs may have been made with the temperature inadvertently set to the lower setting, giving me headaches while the glue was setting as to whether it was going to flow into all the places I wanted it to before it set! –

The coils for the higher frequency bands need less in the way of a link winding, such as 1/2 a turn, which is simply a piece of wire passing through the toroid, but not even being wound around it. For the 16M/17M coil, I found that a 1/2 turn from pin 1 to pin 7 wouldn’t allow the circuit to oscillate, so I used a simple u-shaped loop of wire between pins 1 and 7 placed near the toroid, as in the photo below. The link winding is the green wire. My attempt at using a 1/2 turn link winding for this coil involved a wire from pin 7 through the toroid to pin 1, and this stopped oscillation. However, it’s possible that a 1/2 turn from pin 7 directly through the toroid to pin 4, which is also at ground potential. might allow oscillation while coupling more signal into the detector (it’s a shorter run of wire). I didn’t try it though, opting instead to go for a loop outside of the toroid. Experimentation is definitely key here, and it’s one of the things I had in mind when building The Sproutie. Once you’ve built the receiver, you can still have plenty of fun designing coils for many different bands and amounts of coverage. Here’s that 16M/17M coil, showing the green link winding –

The coil for the 16M BC and 17M ham bands. This one covers 17400 – 18200KHz.

When designing coils for The Sproutie, here are a few things to bear in mind –

Adding capacitance across the coil will bring the overall frequency down, and limit the range of frequencies that the main tuning capacitor will cover (as the tuning capacitor is now just part of the overall capacitance across the coil). However, if you place too much capacitance across the coil, the circuit will not oscillate. When making estimates and performing calculations, remember to include the capacitance introduced by the circuit, and stray capacitances. Another strategy for limiting the range of frequencies the tuning capacitor covers is to put a capacitor in series with it (the tuning capacitor).  If I haven’t already mentioned it, the online calculators on W8DIZ’s site are great for figuring out resonant frequencies for tuned circuits involving toroids. The calculator for the T50-7 is here, and the menu to the left of the page has links for the pages for each of the other toroid cores. Each page also tells you what range of frequencies that particular material is good for. However, even after you think you’ve figured out what values you need for the inductor and capacitors, whether you’re going to use padders, series caps etc, you’ll most likely still have to do some tweaking of values until you get the coverage for each coil that you want, based on observation and experimentation. Once you’ve got the exact values you want, make sure to hot-glue the toroid to the tube base. If you don’t do that, you’ll experience instability and microphony. It’s amazing what difference a couple of dollops of hot glue will make!

For the chassis, I first looked at what was available in off-the-shelf sizes and couldn’t find anything that fitted the bill. Hammond have a good selection of different sizes, but their enclosures, for the most part, use 0.04″ thick aluminum. I wanted something thicker, for a very sturdy structure, so I decided to look into having a custom chassis made. A bit of searching turned up two businesses that manufacture aluminum chassis’ for homebrew tube amp enthusiasts – Dirty Dawg Amps, a US based business who are temporarily out of business due to a fire, and Seaside Chassis Design, who are located in Novia Scotia. Seaside Chassis use a minimum of 14 gauge aluminum for their enclosures. 14 gauge is about 0.064″, which I knew would make for a nice stout case.

Terry was very communicative and straightforward via e-mail about what he could do and what it would cost. I sent him rough drawings, with dimensions, of the chassis, front panel, and mounting bracket for the main variable capacitor that I was hoping he would be able to fabricate. He was able to make all 3 items and on top of that, he would punch all the main holes for me, leaving me just to drill the smaller holes for mounting screws. This was great news, knowing that I would shortly have a solid and well-made chassis on which to build this receiver.

I dropped the ball somewhat and didn’t take a picture of the chassis when it arrived, but here’s what it looked like with all the main components fitted, before wiring it all up. The 2 biggest factors in making this receiver look so grand are the National “N” dial with Velvet Vernier drive, and the excellent chassis. Does this look inspiring or what?

The controls on the upper row are, from left to right – regeneration, the main tuning knob, and the fine tuning. On the lower row, also from left to right is the headphone socket, RF attenuation, the bass boost switch (down = more bass) , the low-pass filter cut-off control, and the AF gain control.

Here’s a view from the back at this point in the construction. Look at that accurately made chassis, front panel, and capacitor mounting bracket. Terry from Seaside Chassis Design did a great job –

Both the RF board (without the extra AF preamp that was built later) and the AF boards installed but not yet wired up. All cables are tagged for easy identification –

Another view of the underside, before everything has been wired up –

The next task was to begin wiring the boards to each other and to the controls. Looking at this view of the underside, I’m thinking that I perhaps could have put a little more effort into dressing the cables more neatly, but it’s perfectly functional. The schematic shows pin 1 of the octal base being grounded but as I was wiring it up, I decided to also ground pin 4 –

Some more views of the underside from different angles and distances. I only twisted the 12V supply lines together for neatness and not for any electrical reason, though it does rather make them look like tube filament wiring 🙂  Just to the left of the antenna socket on the right, is the phono jack for the line out. This is such a useful feature. In fact, as I write this, I am using the line out to record KCBS from Pyongyang on 11680KHz. On the other side from the BNC antenna connector, you can see the DC power jack with the reverse polarity protection diode and the RF bypass capacitors. Vinyl grommets were used for all wiring that needed to pass through the chassis. RG-174/U in the form of Belden 8216 was used for the connection from the BNC antenna connector to the board, and lavalier mic cable with 2 conductors and a shield for all other connections to controls (and to the phono jack) –

A view from the top, with a coil plugged into the octal tube base. The shaft couplers came from different sources. The one on the left, on the main tuning control, is a Jackson Bros part, purchased from Mainline Electronics in the UK through eBay. The coupler on the right was made from all aluminum by John Farnsworth KW2N. He has a small business making these and can also make custom sizes, if you have a non-standard shaft you want to use. For instance he just made a 3/16″ to 1/4″ coupler for my next project. John sells on eBay, but you can also contact him directly through his fledgling website (not yet finished) here. I really like his all-aluminum couplers –

The original intent was to mount the internal speaker on top of the chassis on the side using some kind of simple right angle bracket(s). I didn’t ask Terry from Seaside Chassis to fabricate a bracket for me because at that point, I didn’t know what speaker I was going to use. Looking around my room for something I could use, I noticed an unused LMB Heeger enclosure #143 in the size 4″ x 4″ x 2″ – exactly the same enclosure I used for the 31M version of the WBR. I figured that the top part of the box, being a U-shape, could be used as a bracket. If using that part though, why not use the whole box? There might even be some extra acoustic benefits to housing the speaker in a little case, and having it fully enclosed will protect it from dust and small bits of wire, metal filings etc being attracted to the speaker magnet (which happens here in the shack). The sound was a little “boomy” with the case closed, so I stuffed some foam in with the speaker, and it cleaned the “boominess” right up. Although you can’t really see it in these next shots, the speaker case is bolted to, and spaced off the chassis with 4 vinyl grommets to dampen any unwanted acoustic resonances in the chassis. The speaker wire enters the speaker enclosure through a grommet in the side. It’s a small detail, but the grommet is mounted not in a hole, but in a slot in the side of the cover. That way, when I remove the cover of the speaker enclosure, I can slide the grommet out, leaving the grommet still on the speaker wire, and allowing me to completely remove the cover –

There are a few improvements and modifications I’m considering making to The Sproutie but it is now completely functional, and this is how it looks at this point. I must say that I think it’s looking pretty good –

I was lucky enough to obtain a National “N” Dial in good condition and nice working order – not all of them look or operate this well. I bought several from Gary at Play Things Of Past and used the nicest one. The tuning knob and reduction drive are an important part of the feel of any receiver, and can do a lot to affect the operating experience so I’ll say a few words on that subject if I may. Before, I do, here’s a clip from a page of the 1947 National Radio catalog. I get a kick from seeing vintage parts in old catalogs, then seeing the exact same thing, in really nice condition, in front of me. It’s a bit like meeting a celebrity for the first time 🙂

I was initially concerned that the 5:1 reduction ratio of the National drive wasn’t going to be high enough for accurate tuning on the HF bands – it was a good part of the reason why I chose the value of the main tuning capacitor and wound the coils so as to limit the tuning ranges to around 2MHz or less. This approach results in more coils, but really helps in creating a regen that can be set to a particular frequency, and from which you can read the frequency (with the help of a calibration graph – more on that later.) This receiver can be set to within a few KHz of any frequency. This is good enough for finding a particular SW AM broadcast station. I can also read the dial setting and then consult my custom calibration graph to find what frequency I am on to within a few KHz. It’s not much by modern standards, but is pretty good for a regen with an analog dial.

The National “N” Dial is marked from 0 to 100 and thanks to the vernier scale located at the top, it can be read to one-tenth of a point. These dials, when in good condition, have a firm yet smooth action with no backlash that makes tuning a receiver like this a good experience. Another thing to note is that these dials were manufactured with CW (clockwise) and CCW (counter-clockwise) characteristics, meaning that as you rotate the dial clockwise, the numbers either go up (CW type) or down (CCW type). This makes sense when you consider that variable capacitors were made as units that either increased in capacity as you rotated the spindle clockwise, meaning that the frequency went down (CCW type), or as units that decreased in capacity as the spindle was rotated clockwise, meaning that the frequency went up (CW type). The latter type is the convention for variable capacitors today. When we rotate our tuning knobs clockwise, we expect the frequency to increase. Back in the days when our predecessors thought more in terms of wavelength, they would have expected wavelength (instead of frequency) to go up with a clockwise rotation of the knob. This particular regen uses a CCW-type variable capacitor, so I married it up with a CCW-type vernier dial. It does take a while to get used to the fact that the frequency goes down when you turn the tuning knob clockwise, but I am beginning to adjust. There seem to be quite a lot of these lovely old National “N” dials around, if you take the time to look. A fellow homebrewer told me that his local electronics surplus store had a number of them in good condition for a very good price (I believe he bought them all!) Hamfests and swapmeets are also a good place to look. eBay is another possibility but the prices asked are a bit on the high side, in my opinion. I got mine from Gary at Play Things Of Past. He was easy to deal with.

Note – the National N dials have 3 small rubber/fiber bumpers installed on the mounting plate to prevent the front metal “flange” (the part with the engraved dial markings) scraping on it when the dial is turned.  If your dial is in good condition, none of the main parts are bent, and everything is running “true”, you can remove these bumpers. I did, and the result was a dial that rotated very smoothly. With the bumpers in place, there is a very slight scraping sound as the dial is turned. If you do this, make sure to save the bumpers in case you later wish to re-install them.

One downside to each coil only covering a relatively small part of the shortwave spectrum is that you end up with quite a few of them – more if you decide to wind specialty coils for specific bands. A coil box was definitely in order, so I headed to my local cigar and tobacco shop and purchased an empty cigar box. A trip to the local craft store yielded a length of bass wood, which is a little harder than balsa but can still be cut with a sharp craft knife. I cut slots in the lengths of basswood so they would slot together to form dividers to store the coils in –

The dividers installed in the cigar box, with the coils that had been wound so far (at time of writing this, I now have one more, for the 120M BC band) –

In order to know where you are on the band, you’ll need to calibrate your dial.  I accomplished this by plotting a graph for each coil with frequency on the x axis and dial markings from 0 to 100 on the y axis. For frequency references, you can use a crystal-controlled marker, or off-air signals and an online frequency database such as short-wave.info  Bear in mind that the setting of the regeneration control does alter the received frequency. Probably the best way to standardize your results is to keep the regeneration at or just below the point of oscillation at each dial setting that you take a measurement. The following is one of the graphs I am currently plotting. The original was larger and it is a little hard to read the markings on each axis on this smaller version. That’s fine, as your calibration will be different anyway.  In this graph, look at the line formed by the red dots (the black dots are something different – you can ignore them) –

The variable capacitor I used is what Hammarlund called a “midline” type in which the moving plates (the rotor) were mounted off-center so that the relationship between degrees of rotation and the resulting capacitance was non-linear.  The intent was to keep the relationship between degrees of rotation and frequency fairly linear and by looking at the graph, you can see that it is not bad at all. I also found that once a graph was plotted, I was able to set the dial and return to a particular frequency with a good degree of accuracy and repeatability. When listening to AM stations with this receiver and it’s bandwidth, which is of the order of 10KHz, you can be assured of returning to a dial setting and hearing the station you want.

The Sproutie does work on SSB and CW, but SSB reception is trickier due to the need to control the signal input level (with the RF attenuation/gain pot) in order to prevent overloading of the regen detector and pulling of the oscillator, and to adjust the level of regeneration in order to inject the right amount of carrier. If the signal level to the regen stage is too high, the oscillator will pull, resulting in the signal sounding “wobbly” due to FM’ing of the oscillator. This happens very easily, even with moderately strong signals. My preferred method of operating the set when listening to SSB stations is to run the AF gain at, or close to, maximum volume, and to keep the RF “gain” low. Sometimes, I need to keep the RF gain twisted almost to zero in order to achieve a nice stable demodulated signal. When adjusted properly, SSB sounds good on The Sproutie, but it takes a fair bit more work than with a superhet fitted with a product detector. Hams and shortwave listeners who have used older superhets that used BFO injection into a receiver with a diode detector will be familiar with the technique of keeping the AF gain up high, and using the RF gain to control the signal-to-carrier injection ratio. In this case, we are also using the RF gain to prevent the detector from being overloaded and pulling the oscillator. Sound tricky? If you’ve never done it before, it can take time to get used to, but after a while, it becomes almost second nature.

While I’m on the subject of fine tuning, allow me to expound a little more on reduction drives. In contrast to the friction drive on the National “N” Dial I used for the main tuning, the reduction drive on my fine tuning is a Jackson Bros 10:1 ball drive which has a small amount of backlash and feels a bit “spongy”. I don’t like it, and am grateful that for my main intended use of listening to AM stations, I won’t need it. I may change this ball drive for either another friction drive, or a different ball drive.  The Xtal Set Society sell 6:1 ball drives manufactured (I believe) by Oren Elliot) that have a more pleasing feel. EDIT – I have since found that making the 2 screws that hold this mini ball-drive to the front panel very, very tight seems to eliminate the backlash and reduce the spongy feel a bit.  I suppose it increases the pressure on the bearings a little. For the time being, I’ll keep this drive but if I ever change the front panel, that will be the point at which I’ll drill a bigger hole for a more conventionally-sized reduction drive.

For the above reasons, if I were intending to listen to more SSB and CW on this receiver, I would definitely wind coils to spread each entire amateur band over the whole rotation of the dial, and make sure I had a reduction drive for the fine tuning with very little or zero backlash and a better feel (though having said that, the regeneration control works very effectively for fine tuning).

Another thing that has often interested me is the bandwidth of regens. In general, as you approach the point of oscillation, the bandwidth becomes narrower, until it is at it’s narrowest somewhere around that critical point. As you continue to advance the regeneration, the bandwidth broadens out somewhat. I connected the output of a simple noise generator to the antenna socket of The Sproutie, and took screenshots while running Spectrogram, which was being driven from the line out jack of the receiver.  All 3 of these screengrabs were taken just marginally below the point of oscillation (the ideal point for receiving AM). The first one was with the low-pass filter adjusted for maximum bandwidth –

Well, it’s obviously not the kind of brick wall shape we might expect from a good crystal or mechanical filter but if you look closely, the passband is about 25dB down at the 5KHz point and 30dB down at the 10KHz point, That’s not too bad for AM reception, though if you wanted to get really serious about it, a passband of around 5 – 6KHz with a much steeper wall would, of course, be more ideal.

Here’s a grab taken with the low-pass filter pot at the median point, which is looking better –

…and better still with the low-pass filter set to the lowest cut-off point –

It is important to remember that these spectrums represent the response of the entire receiver, and not just that of the front end. SSB and CW signals become higher-pitched as you tune away from the center of the signal, but although the audio frequency make-up of an AM signal tuned off-center does change, the whole signal does not become higher-pitched. Therefore, an audio filter will be more effective at rejecting off-frequency signals for SSB and CW signals than for AM. Nevertheless, the adjustable low-pass filter is very good at cutting down much of the high pitched static that can make simple receivers like this quite tiring to listen to for long periods whatever mode is being received. It makes The Sproutie feel like a “grown-up” receiver!

Here’s The Sproutie, with it’s coil box. I would have felt as if I had died and gone to heaven if I’d had this receiver as a teenager. I’m feeling pretty good about it at my current age of 50 🙂

The Sproutie is not completely finished yet (is any homebrew project ever truly finished?) The changes and additions I am considering include –

-Designing a thicker, and custom front panel with Front Panel Express, and making it a little wider than the current one to allow for a pair of instrument handles to be mounted

-Changing the 10:1 Jackson Bros reduction ball drive on the fine tuning control for something with less backlash and a firmer, less “spongy” feel

-Winding more coils for specific bands, so that the bands I am most interested in can be spread out over the entire dial, making tuning using just the main tuning control even easier

-I had also considered finding a local cabinetmaker to make a wooden cabinet for The Sproutie, but am not too sure about the convenience of sliding the chassis out of the cabinet every time I want to change a coil. If you’re thinking about building a receiver like this, completely enclosing it in metal would be quite a good idea – perhaps with a hinged flap or door on top for coil-changing. Regenerative receivers are quite sensitive, and this one picks up signals from my computer and/or my monitor, which are located nearby

It always feels good to build something that works, and The Sproutie certainly does that. It’s a great little receiver for shortwave listening and with an extra tube base, a toroid, some wire and a few extra capacitors, you can add whatever frequency coverage to it you like as you go along.

Oh – and I just realized I didn’t explain that Sproutie is the nickname I gave my 2 1/2 year-old cat Sprout, whose ham radio name is Sprat The QRP Cat. I had already named one of my home-brew radios after a kitty I used to have called Rug, so figured it was time to honor Sproutie in the same way.

Sprat The QRP Cat aka Sprout aka Sproutie, after whom this receiver is named.

Videos of The Sproutie in action are here.

Thoughts on using The Sproutie to receive SSB are here.

Sproutie is ever-curious, just like her regen namesake is always seeking out signals.

I continue to update and re-write this post, as I make additions and improvements to The Sproutie. I would rather incorporate them here, rather than into subsequent, and separate posts. That way, if you are thinking of making your own version of this receiver, you can get all the latest updated information by reading this one (rather long!) post, instead of checking my entire blog for updates. As of February 2015, I have filled the entire cigar box with coils, with one to spare (that one is plugged into the receiver). The latest coil I made was for 17400-18200KHz to cover both the 16M BC band and the 17M ham band. 16M is just about the highest frequency shortwave BC band that is in regular use so I now have all the SWBC bands covered – most of them with coils specific for the individual bands. Here’s what my coil box looks like now. The unmarked coil sitting at the top of the box is the experimental one for 24-29MHz –

This cigar box cost $5 from a local tobacconist and makes an excellent coil box. The unmarked ceramic tube base sitting on top is the experimental coil for 24-29MHz. 4 adhesive vinyl bumpers stuck to the bottom help to protect it from rough surfaces.

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