Dave Richards AA7EE

October 15, 2016

Comparing the Weak Signal Performance of a WBR Regen with a K2

The WBR seems to get a bit of a bad rap with some people for it’s sensitivity. A comment on the last post from a reader called Simon, reminded me that some WBR builders have experienced poor sensitivity. Based on my experience, this design does seem to be fairly deaf on AM, but the sensitivity on SSB/CW is fine. I think there are two reasons why some builders experience low sensitivity –

1) They follow the schematic from the original QST article, and do not include an audio pre-amp immediately before the LM386. In this case, the receiver is not necessarily insensitive – it’s just that the low audio is limiting what you can hear.

2) The value of Z1, the inductance between the coil tap and ground, is not high enough. In the original WBR design by N1BYT, this inductance was a 1-inch length of #20 solid copper wire. I followed this direction with my first WBR (for 40M) and it worked well. The WBR was tackled as a group build in the QRP-tech Yahoo Group, as I have mentioned in this blog before, and some builders experienced low sensitivity. The fix was to replace the 1-inch length of wire with an inductor wound on a toroid. Builders in the group found the optimum value of inductance to be somewhere between about 0.2uH and 1uH. I went lower with my 30M WBR, and found that a value of 0.03uH  (3 turns on a T37-6) worked well.

Of the above 2 reasons, my suspicion is that 1) is the main one for most builders.

We regen fans do get a bit braggy about the performance of our sets. I could never make the claim that my regens perform as well as a superhet, for several reasons. Obviously, the strong signal handling of regens is pretty poor, and the bandwidth is wide. When a regen is adjusted close to the point of oscillation, the nose of the response curve becomes quite narrow, but the skirts are still broad. Also, it’s a small difference, but the fact that a regen listening to SSB or CW hears on both sides of the oscillator, as opposed to a superhet, which only hears on one side of the LO, gives the regen an immediate 3dB disadvantage. Basically, for a given signal, a regen is listening to twice as much bandwidth as it needs to (a doubling of power is an increase of 3dB). It’s not a big difference, but it is there.

Having said all that, I am constantly surprised by how much my regens do hear. I remember one evening, a few years ago, when the Russian K beacon was coming through very, very weakly on 7039.3KHz on my K2. I was amazed to discover that I could also hear it on my WBR. Admittedly, I had to strain to copy it on the WBR, and the fact that it was sending the same letter over and over again – and I knew in advance which letter it was, all helped. However, the fact that it was marginal copy on the K2, combined with the fact that I could copy it at all on my WBR (albeit even more marginally) was an eye-opener.

With all that in mind, here’s a 3 minute video of my K2 and 30M WBR side by side, both tuned to the same weak signal, as I swap the same antenna between both receivers. Hope you enjoy it. PS – no cats in this one!

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October 10, 2016

A WBR Regen On The 30M Amateur Band

Occasionally, I drag out old projects from their resting and display positions on my shelf, plug ’em in, and give ’em a whirl. It’s fun to watch as past home-brew rigs come back to life, and relive the feelings of wonder, as a handful of parts that I soldered together actually receive signals and in some cases, transmit them too. For me, the most wondrous times in building are those initial moments when a new receiver begins to pluck signals out of thin air. Those times of wonderment are often stretched out over a period of time, as a new receiver build progresses. I usually start with the AF stage of a receiver, and build backwards. The moment when I touch the input of the AF amp, and hear a mixture of hum and a general cacophony of broadcast stations isn’t so much a moment of wonder, as one of satisfaction that I can put that stage behind me and get on with building the real part of the receiver. Wherever the point is when RF is being converted to AF, and you’re hearing general atmospheric noise, it’s a magic time for me. It only gets better as subsequent stages are added, and the receiver begins to hone in on a very specific part of the RF spectrum. Mind you, there is something quite wonderful about hearing general atmospheric noise – it feels like an audio window into a wider world around us. I love that!

This is a preamble to the resurrection of the WBR that I built for the 31M broadcast band. Although I was initially happy with it, over time, I had to admit to myself that it seemed a bit deaf. Why was that? The original WBR that I built for the 40M amateur band was sensitive enough. Then I remembered that on the few occasions I had used to it to listen to 41M SW broadcast stations, it had also seemed a bit deaf. Perhaps it was just something about this design that doesn’t do well on AM? With that in mind, I decided to see how my 31M WBR performed on the 30M amateur band.

The existing receiver was already covering 9400 – 10000KHz, and a gentle adjustment of the trimcap in the tank circuit raised the frequency so that it was covering the 10100 – 10150KHz amateur band. The only other adjustment to be made was to limit the coverage to the 50KHz width of the amateur band, as it had previously been set up for the much wider 31M broadcast band. This can be accomplished by adjusting the range of voltages that are applied to the varactor diode, which usually involves nothing more complex than a judiciously placed resistor or two. I placed a 68K resistor between the bottom of the tuning pot and the trimpot, and changed the value of the trimpot from 5K to 10K –

The trimpot is used to set the lower edge of the band coverage, and the 10K value didn’t give me much adjustment range. I managed to get things set the way I wanted them, but suggest the values in parentheses, of 56K for the fixed resistor and 22K for the trimpot, as ones that would give more room for adjustment. If you’re building this from scratch, it might be worth looking into the use of 1N4001’s for the varactors. They’re cheaper and more widely available, and although they don’t give as wide a capacitance range as most varactor diodes, not much is needed when you just want to cover a 50KHz-wide band. You’ll probably need different values for the fixed resistor (if you even need a fixed resistor) and the trimpot. I’d start with no fixed resistor, a 5K trimpot, and go from there, if you do decide to experiment with a different part for the tuning diode.

The resulting receiver works well on the 30M band, with good sensitivity. Indeed, sensitivity is rarely an issue with regens – their main weaknesses are poor strong signal handling, and lack of selectivity. I have not yet heard a signal on my K2 that I couldn’t also copy on the WBR. This confirms my growing suspicion that this design just doesn’t cut it for AM, though it performs well on SSB/CW.

Another feature of this particular WBR version is the circuit of the LM386 AF amp, which provides enough gain to easily drive a speaker, and seems to have less noise than other high-gain configurations of this chip. I’ve heard from folk who built the WBR as described in the original QST article, and have been told that it has low audio. If you’re going to use that circuit, I strongly recommend that you include a preamp stage, as detailed in this post. Even better would be to use the circuit of the 31M WBR which, as well as including a preamp, also has the higher gain and lower noise LM386 amp stage.

If you’re into experimenting, Joel KB6QVI just bought some MD8002A audio chips from eBay. He reports that they have high gain (just like the LM386 in it’s souped-up circuit configurations) but, unlike that chip, is low noise. Like the LM386, it is intended for battery operation, so has low quiescent current. I’m thinking this chip could be a great substitute (not direct pin-for-pin though) for the 386 in many of our favorite well-known simple ham projects. Just a thought 🙂

I’m really happy with how the WBR performs on 30M. It would make a neat receiver for a simple QRP transmitter running from a 10.106MHz crystal. Here are 3 videos. The first one is probably more informative, though the third one includes 2 of my cats 🙂 I do tend to say some of the same things in all the videos, so apologies for the repetition, though I keep it more brief in the first one. If you’re only going to watch one video, watch this first one –

There was a lot of local noise during the recording of this next video. On top of that, I had not set the regen control properly. The set was well into oscillation, making it sound “hissier” than necessary. It also broadens out the response somewhat –

Once again, with this video, I had the regen control set too far into oscillation, widening the response and creating a bit more hiss than necessary. Really, if you’ve watched the other two, the only reason to watch this one is if you want to see some kitty action (2 of my gals feature in this one, beginning at around the 2 minute mark –

That’s the WBR on 30M, and I’m really happy with how it performs there.

 

February 3, 2015

N2HTT Builds His First Receiver – A WBR Regen!

A few weeks ago, I received an e-mail from Mike N2HTT. He was building a WBR Regen, and had encountered a problem – the pesky thing didn’t work. That is indeed, quite a problem.  Luckily for me, he quickly discovered that the reason was an incorrectly wired JFET, before I had a chance to confuse him with my impaired troubleshooting skills 🙂

He got his WBR up and running in short order and after casing it up and actually labeling the controls (only very serious home-brewers label their front panels!), reports that it is working well. He’s tickled pink, because it’s the first receiver he’s built – and I’m tickled pink because he’s tickled pink, if that makes any kind of sense. There is a real magic that springs from hearing sounds come out of a speaker or headphones connected to a receiver you built yourself – even more so if you scratch-built it, as Mike did with his WBR. You can read the story of his WBR build here, and this post contains a link to a YouTube video of his WBR. I like how he describes the setbacks he encountered along the way, and how he dealt with them. In fact, looking further at his blog, I realized this was a common theme. Mike doesn’t just tell you what he did, and post a few photos; he effectively describes the odyssey of his life as a ham who is embarking on the task of assembling a station he built himself.  This style of narrative shines through in the 3 posts describing his building of a 2 tube W1TS transmitter for 40M. You can find them here – Part 1, Part 2, and Part 3.

Look at this lovely transmitter. It’s a classic home-brew project – it’s got an aluminum chassis, a tube, and a crystal in an FT-243 holder!

N2HTT’s version of the W1TS transmitter. Photo courtesy of N2HTT.

Mike was also featured in Soldersmoke for his Michigan Mighty Mite Build, as part of Bill Meara’s Mighty-Mite Madness, not once, but twice – here and here.

So Mike has got it going on. He’s building things, he’s making them work, and he’s telling us the stories of how he got them to work.

Here’s his WBR, in all it’s cased up glory. Read about it here, and here. There will be a 3rd post too, in which perhaps we’ll see pictures of his other WBR which he put on 80M. Yes, that’s right – Mike didn’t just build one WBR – he built two, thanks to the incorrectly wired JFET (you can read how this story unfolds in his blog).

N2HTt’s WBR Regen Receiver. Photo courtesy of N2HTT

Check out Mike N2HTT’s blog here. Way to go Mike, and thank you for sharing details of your personal journey towards a 100% home-brew station!

 

 

 

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!

June 24, 2014

Building A WBR Regen Receiver For The 31M Broadcast Band (or the 30M Ham Band)

Note – some of the narrative in this blog-post assumes that you have access to, and have read, N1BYT’s original article on the WBR Receiver in the August 2001 edition of QST.

EDIT – as of July 2016, I just modded this receiver to cover the 30M ham band only, and have been surprised by it’s sensitivity. My WBR’s appear to be more sensitive on SSB/CW than AM.

It has been almost 3 years since I first built N1BYT’s WBR – a regenerative receiver for the 40M amateur band. It was an intriguing design for me, as it employed a Wheatstone Bridge arrangement to minimize oscillator radiation into the antenna without the use of an RF amplifier stage. Unlike older tube designs, more modern semiconductor regens don’t generate as much RF energy, though although you might think that the need for minimizing radiation into the antenna is less, that is not the case. Radiation into the antenna can be the cause of one malady that plagues some regens – that of common mode hum. This circuit avoids that. It is quite a unique design. In fact, unless I’ve missed something, you have to go back to the 1920’s in order to find anyone who was designing along the same lines, as Mike Rainey AA1TJ relates in this post of his.

Such was my pleasure at the performance of this little receiver, I have often wondered how it would adapt to other frequencies. I did briefly try to make a general coverage version of it but for some reason, couldn’t get the oscillator stage to oscillate and gave up on it far too soon. Then, a few weeks ago, I started wondering about building a second WBR, for the 31M shortwave broadcast band. I already had a small aluminum enclosure into which I knew I wanted to put the finished receiver, and some months earlier, had cut a piece of PCB for whatever Manhattan project would find it’s way into the box, so getting the envelope of MePADS and MeSQUARES out and beginning to build didn’t take much of a leap, once I had found the initial inspiration.

A few rough calculations revealed the number of turns that would be required on the toroid for this new, higher frequency coverage, and they proved to be correct. I guesstimated that I should be able to achieve something of the order of 500KHz of coverage, which would allow the receiver to tune the 9400-9900KHz 31M band. I was also hoping to be able to cover up to 10MHz in order to be able to receive WWV and as it turned out, that was indeed possible. As well as a new frequency range, I decided to try a different configuration for the LM386 AF amp. N1BYT uses the 386 in it’s standard high-gain configuration that places a 10uF capacitor between pins 1 and 8 of the chip.  This has the advantage of providing high gain with low component count (an important consideration if you are to engage as many builders as possible), but it is also an approach that results in a lot of hiss. If you’re using a regen, you’re already dealing with a fairly high amount of hiss, so I wanted to at least remove some of that from the audio stages. In his Micro 40 DSB transceiver, Peter VK3YE uses the LM386 in a way that still gives high gain, but is a bit less hissy. Much has been written in the pages of SPRAT on trying to eke more gain from this venerable and much-maligned little chip, and Peter’s circuit appears to be based on LA3ZA’s ideas in SPRAT 116 (page 4). This circuit worked well in the Micro 40 I built, so I decided to use it in this, my second build of the WBR. I also incorporated a pre-amp stage, as suggested by N1BYT in his original article in the Aug 2001 issue of QST.

On completing the receiver, I noticed that it seemed a little deaf. The WBR was a project in the QRP-Tech Yahoo Group (Yahoo membership required), led by Chuck K7QO, and a few builders there also experienced lack of sensitivity. I am wondering if they made the same mistake that I made with both my builds of the WBR – to miss the fact that the full details of Z1 were not published in the original QST article. A later list of corrections revealed that Z1 was intended to be a metal strip measuring 1/8″ x 1/2″ and connected to ground via a short wire. In both of my WBR builds, I used a piece of stiff wire instead of the recommended metal strip, as detailed in the original article, and was perhaps inadvertently placing too little inductance at Z1.  Although Dan N1BYT does warn against increasing this impedance, lest it lead to detector overload, LA3ZA found that an inductor of 0.22uH at this point helped the sensitivity (and presumably didn’t overload the detector). Builders in the QRP-Tech Yahoo group experimented and found values between 0.22uH and 1uH to be optimum. I followed a slightly different route, first adding a 0.3uH inductor, consisting of 9 turns wound on a T37-6 toroid core. This increased the sensitivity dramatically, but also resulted in breakthrough from a local religious broadcaster on 1640AM. Instead of experimenting with lower values of inductance, for some reason, I added a simple BC band trap. At first it appeared to solve the problem, but then I noticed that although the AM breakthrough was much diminished, it was not, in fact, completely gone. At this point, I reduced the number of turns on my T37-6 from 9 to 4 and found that it did the trick. My WBR was still quite sensitive, yet without the disadvantage of breakthrough from strong broadcast signals. I left my BC band trap in circuit but would suggest if you build this circuit, you first experiment with the value of the inductor before deciding whether to add the trap.  Keep the value of inductance as low as possible and depending on where you live, a trap may well not be necessary. EDIT – Jason NT7S has also built a WBR using the schematic published here. He reduced the number of turns on his inductor to just 3 and found no need for a BCB trap, despite having a strong local station at 1390KHz that was causing detector overload when the number of turns on his inductor was 4. It pays to experiment! See the bottom of this post for more info on Jason’s experience with the BCB trap and for a video of his WBR in action. Jason also found that the BCB trap I detailed here does not have an ideal response. Details of that are at the bottom of this post.

I know there are some experimenters who are sitting on the sidelines waiting to build a WBR, but who are a little confused by the various mods published, and want to see more information on a successful build before going ahead with their own. By sharing detailed information on mine, I’m hoping a few more people will be encouraged to build their own version and share their experiences – the internet is a great way to do this. Many thanks to Dan N1BYT for graciously giving me the go ahead to show you a full schematic for this version that I built. The only changes I made to the core part of the circuit (the regen stage and the infinite impedance detector) were to employ a 10-turn pot for the regeneration (with a 33uF cap across it to stop the “whizzing” sound), the addition of the trap, and the substitution of Z1 for a small toroidal inductor, a mod that was first publicized by LA3ZA. The actual value of this inductor may require experimentation on the part of the individual builder but, and this does bear repeating,  it is wise to err on the side of keeping it small in order to avoid detector overload. My 40M WBR uses just a piece of stiff wire for Z1, and I have never heard any kind of breakthrough from all the signals my outside antenna deliver to that defenseless little receiver!

If you are thinking of using the optional AM BC band filter, I have since discovered that the attenuation of this filter is not as high as I had hoped. Give this one a try instead. It uses molded chokes instead of toroids, which some builders may prefer.

 

The description of circuit operation is contained in the original article which is readily available to ARRL members. Having read horror stories of unstable and unpredictable regen behavior by some builders (not of the WBR, I hasten to add), I was pleasantly surprised to find that the WBR has smooth regeneration control with no hysteresis, and is overall a tame set to operate. I have read that for solid state circuits, the designs that incorporate a separate Q-multiplier and detector (as does the WBR) tend to work better. Whether this is fact or hearsay, I am not sure. I have found it quite difficult to separate technical fact from folklore in the area of regens. This could be partially due to the fact that many builders, like myself, don’t have an in-depth knowledge of the workings of these circuits. Add that to the fact that regens are particularly dependent on good RF practices and solid physical construction, and I suspect that some designs are declared to be wanting simply because the experimenter didn’t build it properly. Likewise, due to lack of knowledge on the part of many builders, marginal regen designs are published and propagated by people who don’t have the ability to discern whether a circuit is “any good” or not. The world of regens seems to be a mystical and magical one inhabited by equal parts myth and fact.

I used 10-turn wirewound pots for both the regeneration and tuning controls (Bournes 3590S-2-103L). These pots aren’t cheap and if you need to save money, you can use a preset to set the approximate regeneration voltage range, and a regular 1-turn pot for the regen control, as N1BYT describes in the original article. A 10-turn pot does seem to give more precise control over the regeneration though. If you use a wirewound pot here, add a 33uF capacitor between the slider and ground, as shown in the schematic. This will eliminate the “whizzing” sound as you rotate the pot. I have an affinity for 10-turn pots, so I used them for both controls. I like the fact that I don’t have to bother setting the approximate regeneration range with a preset, as I have the full range of control voltages available to me immediately with the 10-turn control. The 10-turn seems to give better control over setting the receiver for the threshold of oscillation. Also, when using the injection of carrier to receive weak AM stations, the regen control can be used as a very fine tuning control in order to set the receiver to zero beat when in exalted carrier reception mode. Adjusting the regen control does have the effect of slightly shifting the frequency of the receiver, which can come in quite useful when wanting to make critical adjustments to the tuning of the receiver. Incidentally, this is a good reason to pay close attention to the physical construction of your WBR. You won’t be able to set the receiver for exalted carrier reception if it’s not stable enough.

The one disadvantage of using a 10-turn pot for the tuning is that you can’t see at a glance roughly where you are in the band. An arrangement of two 1-turn pots, one for bandsetting, and one for bandspread, will be cheaper, and will allow the operate to easily judge where he is in the band simply by looking at the setting of the main bandsetting pot.  Other arrangements might be possible. One thought that comes to mind is the use of an old-fashioned vernier reduction drive with a logging scale connected to a 1-turn pot. This would allow for quite accurate calibration of the dial and of course, the ability to see where you are in the band with one glance. The expense and trouble may not be justified, but if you already have one on hand, it would be an intriguing option. Expanding on this – how about a version of the WBR with plug-in coils for wider coverage? The padder and trimmer capacitors could be included in the coil form so that each frequency range could be adjusted individually. Well – that may be too fanciful an idea, but imagination is free! If you’re using a 10-turn pot, how about one of those turns counter dials combined with your own personalized logging chart? This is an idea I may try to implement in my build of this receiver at some point.

When setting the frequency coverage, you can run a short piece of wire from the antenna lead of a general coverage receiver close to the main tuning coil of the WBR and turn the regen control in order to make the set oscillate. Then, listening to the WBR oscillator in your receiver and with the tuning pot in the WBR turned fully clockwise, set the trimcap for the uppermost end of the desired frequency coverage. Twist the WBR tuning pot fully counter-clockwise, and use the 5K trimpot to set the bottom of the tuning range. With the values given, I was able to get my WBR to receive as high as 10.3MHz and lower than 8.6MHz, giving me the ability to pick any 500-600KHz tuning range within those limits. It would be a fairly simple matter to set the WBR to receive on any desired band of frequencies by changing the number of turns on the coil and/or the value of the 47pF padding capacitor (the capacitor in parallel with the trimcap).

Here’s the basic board. At this point, the only inductance between the center-tap of the main tuning coil (the big one on the yellow T68-6 toroid) and ground is a short piece of stiff wire.  Also, the AM BC band trap hasn’t been built yet (I didn’t know that I would need it). The cables for the various connectors have been bundled together in order to look neat for the picture –

On connecting this board up, the receiver seemed a little deaf, To be fair, although the original article doesn’t mention it, corrections to the article published in a future edition of QST did mention that Z1, the impedance between the center-tap of the coil and ground, should have been drawn as a metal strip 1/8″ wide, 1’2″ long, and grounded to the board with a standard piece of wire. I was using just a piece of wire, as you can see in the photo. This probably wasn’t providing enough inductance. I clipped part of the wire connecting the center-tap to the ground plane, and inserted an inductor consisting of 9 turns of wire on a T37-6 toroid.  This is an inductance of about 0.3uH. Wow – what an improvement in sensitivity! Unfortunately, a local broadcaster whose transmitter on 1640KHz is just a few miles down the road from me, was breaking through. This was presumably caused by detector overload as a result of increasing the impedance at Z1. I added a simple AM broadcast band trap which I initially thought had solved the problem, but later discovered that the breakthrough was still there, albeit at a much lower level. I rewound the T37-6 toroid with 4 turns, for an inductance of about 0.05uH. Bingo! Breakthrough gone! In retrospect, a better way to proceed would have been to attempt to find an optimum value for the inductor that would have given good sensitivity while still avoiding overload of the detector, before adding the trap. Here’s the board after the trap was added, and the center-tap of the coil modified. The stiff wire to ground was cut and a 10M stand-off resistor inserted in it’s place to help with rigidity, before adding the inductor wound on the T37-6 toroid. This is the first version of the inductor, with 9 turns. The later version had just 4 turns –

Time to box it up. I’ve had a couple of small aluminum cases from LMB Heeger that I bought because I thought they’d make great cases for small projects.  It’s their model #143 in plain aluminum finish, though it is also available in grey and black. One thing I particularly like about it is the small lugs on the top cover – 2 at the front and 2 at the back – that prevent the front and back panels from flexing inwards. This feature helps to make it a very stout little case. This enclosure was the obvious choice to make a nice compact receiver out of this version of the WBR –

 

After a few hours of listening to it (what fun!) the AF amp began to make occasional motorboating-type noises. It appeared that audio peaks were changing the regeneration point and pushing the set into slight oscillation. The battery was still at about 8.5V, so this should not have been happening. While researching possible causes, it occurred to me that in reality, this receiver was going to spend nearly all of it’s time in my shack, meaning that I could run it off the shack gel cell power supply. Instead of solving the issue I took the easy way out, removing the battery holder and fitting a jack for a DC power supply, along with a series diode for polarity protection. The receiver can easily handle the ~0.6V voltage drop from a 12V supply, and if you use the reverse diode to ground method with a bigger 12V supply, it will blow the diode like a fuse if you inadvertently connect the power to the set the wrong way round.  With a small 9V battery, it’s internal resistance should prevent it from passing enough current to blow the reverse diode. Also, you cannot afford to drop 0.6V from a 9V supply, hence the reason for using the method pictured in the schematic. The holes that were previously used to mount the battery clips became tie points for the antenna cable –

My downstairs neighbor’s cat was standing over the WBR in this next shot. You can see his whiskers in the top right-hand side of the frame. I think he’s interested in regens. In these next 2 shots, you can also see the lugs on the top cover that help to make this such a stout little case. It’s a neat little receiver –

From time to time, I am asked what knobs I use for my projects. They are manufactured by Eagle Plastics. I get them from Mouser, though I’m sure they’re available through many other outlets.

The large one I use for tuning is part # 450-2039-GRX (the exact same knob is also available from Radio Shack, and is RS catalog # 274-402

The medium sized ones I normally use for AF gain, RF gain etc are part # 450-2035-GRX

and the small ones I use for AF gain, RF attenuation, and regeneration in this receiver (because space was at a premium) are part # 450-234-GRX

For wiring up the connectors, I use a thin cable consisting of 2 conductors plus a shield. It’s made for lavalier mics, so is skinny and flexible – ideal for wiring up pots and jacks. I used to get mine from a local pro-audio store that recently closed down, so had to find a new supplier. Most places online seem to either want to sell large reels of the stuff or, if they do sell it by the foot, charge too much. I found a place in Connecticut called Redco that sell it by the foot for a reasonable price. On top of that, they will ship via first class USPS mail, which helps to keep the cost down. I haven’t tried any of this new batch yet, but it’s a quality cable made by Mogami (type W2697), and it looks like it will do the trick.

RF connections (like from the antenna connector to the RF attenuation pot) are made with Belden 8215 RG-174/U.  It’s skinny and flexible.

Following are a number of videos designed to show different aspects of this regen, My old camera takes awful quality video (sorry about that) and limits the clips to 3 minutes, which is why there are several videos instead of one long one.

This one shows how the set has quite a narrow bandwidth when set to the point just below oscillation. In all these videos, the WBR is directly driving an external speaker. There is no external amplifier connected –

In this video, you can hear how the audio bandwidth broadens out considerably when the set is oscillating –

Tuning around the 31M band. There aren’t many strong signals, as band conditions generally have been poor. It’s not due to any shortcomings in the WBR –

This video shows how stable a homebuilt regen can be. I could have made mine more impervious to knocks by holding the toroid with a nylon screw and washers, but that might have introduced more long-term drift –

Another video just tuning around. It cuts off rather suddenly at the end –

This one shows how effective the technique of exalted carrier reception can be – and you can do it with a regen! –

It seems fairly sensitive, and quite stable, both in terms of it’s response to physical knocks, and the long term drift. I like regens over direct conversion receivers, because of their ability to demodulate AM as well as CW and SSB transmissions. I suppose that with a very stable VFO (a synthesized one perhaps) a DC receiver could receive AM in exalted carrier mode but with a regen you can actually take it out of oscillation and receive AM with no carrier injection. The regenerative detector is a versatile one.

The only criticism I have of this particular build of the receiver is that I seem to have a noisy LM386. The 386 stage is generating a type of low frequency random scratchy noise that wasn’t present the last time I used this circuit configuration (in the Micro 40). I have heard that there is enough variation in these chips such that you can get a particularly noisy one. This chip was part of a batch of cheap ones I bought from eBay. I just ordered some LM386N-4’s from W8DIZ. They seem to be quality parts from National Semiconductor and because they are LM386N-4’s, they have higher power dissipation and a higher max supply voltage (16V) than the others (12V), which can’t be a bad thing. I may, at some point, put one of Diz’s 386’s in place of my eBay cheapy-chip in this set.   EDIT June 25th 2014 – I just replaced the eBay cheapy LM386 with an LM386N-4 from W8DIZ and the scratchy rumble is gone! The ones that Diz sells are National Semiconductor devices and of course, they still hiss, because they are 386’s being used in a high-gain configuration. With a good 386 though, the noise is just a smooth hiss that is much easier to deal with than the scratchy rumble of the bad part.  Here’s what the sub-par IC sounded like. The hiss is normal for a LM386 used in a high-gain configuration, but that scratchy rumble is most definitely not –

Jason NT7S built a WBR using the schematic in this post. Instead of building it for the 31M band, he built his for the 40 amateur and 41M broadcast bands. If I remember correctly, he set his coverage for 6900 – 7500KHz, which gives him coverage of the pirate BC band at around 6925KHz ±, 40M from 7000-7300, and 41M from 7200 – 7450KHz, though it does make tuning SSB and CW a bit tricky. If you want to make tuning SSB/CW easier, then you can limit the coverage of a 40M RX to just the amateur band. If you’re a hpone-only person, you could have your WBR tune 7150-7300 (in the US) for much smoother tuning! Before removing a turn from his antenna-input inductor, Jason was getting breakthrough from a strong local station on 1390KHz – even with the AM BCB trapin place. He did a sweep of the trap on his scope and here was the result.  The marker is at 1390KHz – the strong undesired signal –

Note how the attenuation of the trap is only about 5dB at the frequency of the unwanted signal. I may take another look at the values of the components in this trap with a view to increasing the cut-off frequency but my first step will be to also remove a turn from my antenna-input inductor to reduce it to just 3 turns and see if I can also manage without the trap.  Thank you for this input Jason!  Jason’s WBR sounds great. It is the first time he has successfully built a regen, and I’m tickled pink that I was able to inspire him to build this one. I don’t think he was disappointed either –

Jason sent me this picture of his WBR, all wrapped up in a smart blue enclosure.  Aluminum for the bottom half, and PCB material for the top half, if I’m not mistaken. I like the attractive pattern of holes for the speaker cut-out. Is the bottom half from an LMB Heeger Crown Royal enclosure, by any chance? Nice! –

Jason NT7S’ WBR in it’s attractive blue enclosure. Jason built his for coverage of 6900KHz – 7500KHz.

This successful build of another WBR is helping to pull me down the rabbit hole of wanting to build the perfect regen. My goal is to build a really good general coverage regen on a nice-sized chassis with plug-in coils for band changes. I am starting to collect parts with this goal in mind and being relatively inexperienced with regens, have many questions in my mind, such as

– semiconductors or tubes?

– separate detector and regen stage, or an oscillating detector?

– an FET or a bipolar detector?

– high mu, or low to medium mu tubes for the detector?

– throttle capacitor with ball drive, or resistive regeneration control?

– toroids or traditional coils?

– any other considerations?

Although I’m secretly looking for a solid technical reason to make my dream general coverage regen a tube design, a semiconductor one would probably be best, as long as I’m not potentially giving up anything in performance. If any experienced regen builders are reading this and have any ideas, I’d love to hear them.

Oh – and the downstairs neighbor’s cat, whose whiskers you saw poking down from the top of the frame in the shot of the WBR from the back? That’s Stephen. He likes regens (I think). Here he is wondering what magical electromagnetic signals there are out there in the ether. He might also be looking at a bug –

Such an enjoyable little receiver. Thank you for the circuit once again N1BYT.

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.

January 31, 2012

QRP CW WAS, KA0XTT and W0O, WBR Receiver, and NT7S To Give Seminar at FDIM

Phew – quite a headline there.  I suppose if I were a more organized blogger, I’d break this into several different topics and get several blog-posts out of it.  However, I’d like to get it all out of the way, and get this info imparted to you in one fell swoop, so here goes.

After completing the Norcal 2N2/40, I got to thinking that it would be really neat to achieve WAS with it – that would be QRP CW WAS on just the one band – 40M. I didn’t get close unfortunately, though I didn’t make a concerted effort either.  On completing the K2, all the other QRP rigs with the exception of the CC-20 were packed up and put into a box; I wanted the operating desk cleared and simplified so I could spend time with my precious new fixation – the K2. With that, the prospects of QRP CW WAS with the Norcal 2N2/40 faded somewhat, but I realized that with the multiband capability of the K2, achieving QRP CW WAS should be pretty straightforward – and it was.

In my entire amateur radio career, I have never won any kind of award – and I’ve been licensed since 1978.  This has been due mainly to very occasional periods of activity interspersed with longer periods of inactivity; a pattern of operating that I know I share with quite a few other amateurs. I’m also not a very competitive person, but it seemed that it was about time I qualified for something, and QRP CW WAS seemed like the obvious first choice.

Not much to say really.  I operate almost daily, and many of those QSO’s from normal operating provided QSO’s for WAS. Add in the odd contest here and there (the ARRL 10M Contest was very helpful, as was NAQP).  Predictably, as my list of states still needed got down to a mere half-dozen, Delaware and Rhode Island were in that list. Luckily, NAQP allowed me to nail both those states through QSO’s with WW3DE and W1WBB.  At the end of my last blog-post, I asked if anyone could give me a QSO with WV, as that was the last state I needed. Frank KA8SYV very graciously responded and did indeed give me a QSO with West Virginia.  It was quite fitting that the QSO with Frank was the one to complete my WAS, as it was he who bought my FT-817 back in June of last year.  We did try to make the QSO with his FT-817, but I couldn’t quite copy his sigs, so he went up to 100W, and the difference was like night and day. Luckily he copied the 5W sigs from my K2. Thanks Frank – your 40M loop was doing a fine job.  Not only was the personal connection with Frank a good reason for him being the final QSO of my WAS attempt, he has an excellent QSL card too, which gave me another reason to want a QSL from him. Here it is:

Frank said that so many people commented positively on that image that he had it made into a QSL. I love it! A few days after receiving it, a card arrived in the mail from John N8ZYA, for a QSO we’d had a few months earlier.  John noticed from my blog that I needed a confirmation from WV and sent me his card.  How did I miss that WV QSO when looking back through my log? Even more perplexing is that John and I have exchanged e-mails and blog comments before, so are well familiar with each other.  Aah well – better to have too many confirmations than too few. Thank you John.  For dog lovers, my Alabama QSO provided me with this QSL:

I now have all the contacts I need. I am waiting for one confirmation from W1SJ in Vermont, but his QRZ page states that QSL’s are generally answered 6 weeks after a contest, so I have every reason to believe that a confirmation from him is forthcoming. When it arrives, I’ll be able to apply for a WAS certificate from ARRL, or if I want to stick to my original goal of having a paper QSL from each state (and not just a combination of paper and LoTW) then I think there are one or 2 more states I need paper QSL’s from. However, they are all states with which I have enough insurance QSO’s so it’s not a problem.  I’m not sure if I will even apply for the certificate. I’ve already achieved WAS. Once the confirmation arrives from W1SJ, I’ll have confirmation that I’m in the log in 50 states for QRP CW contacts and that’s enough for me. Mission accomplished!

Yesterday morning, a QSL I’ve been hoping would materialize actually did. It was for a contact I made with special event station W0O in Frankenstein, MO on Oct 31st. What a fine card. I can’t think of a more fitting QSO on Halloween than with a station in Frankenstein. Thank you very much to the Mid-MO Amateur Radio Club:

The postmark on the envelope was equally impressive. Can you see the word “Frankenstein” spelled out in the tree branches?

Another QSL to arrive yesterday was this one from the fictional TV character Mike Baxter KA0XTT, played by Tim Allen in the series Last Man Standing.  In return for my QSL, the production team sent Mike’s QSL, autographed by Tim:

A group of hams on Twitter decided to send our cards in as a bundle together in the hope that our cards will all be displayed on the wall at Tim’s operating position in a future episode.  I suggested that they send their cards to me so that I could send them on their way, my reasoning being that as I’m in California, the last leg of the trip will be a day or two quicker. Here are the cards from our Twitter group before being bundled up and sent to Studio City:

N9VN and KE7JTU’s cards didn’t arrive for some reason. Perhaps they will be the subject of a QST article in a few decades along the lines of “QSL cards long considered lost finally arrive 30 years later”!

In other news, I was excited to be able to contribute some text and photos to the next edition of the ARRL book “Low Power Communication” written by Rich Arland K7SZ. The subject will be my build of the WBR Receiver, which has generated quite a lot of interest. Poor Daniel N1BYT must be getting a bit fed-up with the renewed interest in his excellent regen receiver design, 10 years after it was initially published in QST.  I noticed that his e-mail address has disappeared from his QRZ page and did wonder if he did it so that we’ll all stop bothering him with questions about the WBR! It will be the project for the group build at this year’s OzarkCon, a number of people have commented to me that they have also built, or are building, their own copies of the WBR, and at least 2 individuals/groups have expressed interest in making a kit of parts available, though I don’t know whether a kit will materialize. To this day, the post on this blog about the WBR is by far the most popular, consistently receiving more views than any other post. Thanks Rich – I have never had anything I’ve written or taken pictures of published in a book before, so this will be thrilling!

Last but very definitely not least, the news has just come out that Jason NT7S will be heading up a seminar at FDIM this year. While I know that he would be well-equipped to talk about the logistics of providing day-care for a toddler and a boisterous (yet affectionate) golden lab, while still managing to find time to design circuits and occasionally even operate on the air, the tentative subject of the talk will be the use of free and open source tools in the development of his products, but he may tweak the subject and content of the talk as time progresses.  If you want to learn about etherkit and Jason’s planned product line, FDIM this year will be a good place to be. He will also have a vendor booth.

August 13, 2011

Video Of WBR Regen

I finally got around to putting up a video of the WBR Regen on YouTube. Unfortunately, I didn’t get many good recordings of SSB – this was mainly due to band conditions and the times of day that I was recording. However, it was time for me to get this thing out so that I can move on. First plan is take a break this weekend. I never quite know for sure what my next project will be or when it will begin. This is a hobby and I simply follow my interests:

July 24, 2011

The WBR – A Simple High Performance Regen Receiver for 40M by N1BYT

EDIT (July 26th 2014) – If you’re thinking of building the WBR, I strongly suggest you check out my most recent build here, which incorporates a mod suggested by LA3PNA, and a different configuration for the AF amp that I think provides nicer sounding audio. The full schematic is published there also.

A few weeks ago when a sizable order of parts arrived from Dan’s Small Parts And Kits, the plan was to use them (along with the parts from a few smaller orders from kitsandparts.com and Mouser) as the basis for some fun home-brew projects. I got my feet wet by building some small circuits Manhattan style – an audio filter and RF preamp for my VRX-1 DC receiver, and a crystal oscillator in an Altoids tin to check out the MeSQUARES I had just received from QRPMe. These are detailed in recent posts.

Like anyone who builds circuits, I have a mental list of things that I’d like to build which is updated constantly.  Some ideas get pushed to the back of the queue to make way for newer ones, and some stay pretty close to the front for long enough that eventually opportunity and desire collide and magically, it gets made. This is what happened with the WBR regen receiver.

As a teenager growing up in England, I had a one-tube shortwave regen that I built from a kit.  It was an HAC Model DX which used a mere handful of components and used a big rectangular 90V battery for the high tension supply.  It used plug-in Denco coils for band-changing (I think I remember having 3 of them).  I spent countless hours in my bedroom with the high-impedance headphones clamped around my ears, constantly tweaking the regeneration and tuning capacitors and listening mainly to shortwave broadcast stations.  I could figure out which band I was on, but had little idea of the actual frequency.  It really didn’t matter though, because the likes of Radio Australia, Radio Tirana Albania, Radio Moscow, Radio Nederland’s “Happy Station” shows, Radio Prague and many, many more kept me glued to that little set. It was just a small bent aluminum chassis with 3 variable capacitors,  a battery triode, a set of headphones, a coil, 3 fixed resistors and 2 fixed capacitors, but it was pure magic to me.

I think I spent the majority of my teenage years in my bedroom, listening to my record collection and radios. As an adult who recently semi-retired, it feels as if I’ve come full circle.  The chance to spend all the time I want building and listening to radios is an absolute gift, and the WBR Regenerative Receiver (Aug 2001 QST) that I’ve had the pleasure to use these last few days has brought the magic of radio listening back in a big way. It is sensitive, very stable, suffers from no microphonic effects at all, and thanks to the ingenious Wheatstone Bridge tank circuit has very minimal radiation of the local oscillator signal from the antenna port and so no common-mode hum problems.  Oh – and no hand capacitance effects either. I haven’t yet measured the drift, but after I’ve switched it on and let it warm up a little, I can set it to a frequency to listen to a net or QSO, and it stays there. Obviously, there must be some drift, which I hope to measure soon, but I’m not hearing any.  One more thing, not only is there little long-term drift, but my unit is very frequency-stable when subjected to physical shock too.  It’s a great little receiver and has pleasantly surprised me with it’s performance.

I won’t be publishing the schematic for the WBR receiver here, as it’s not mine to publish. (NOTE – Dan has since said he doesn’t have a problem with me publishing the schematic, so I went ahead and published the schematic for the slightly different version I made for the 31M band here.)  It appeared in the Aug 2001 edition of QST, so if you’re an ARRL member, you should be able to download it from their site. The article was also reprinted in the ARRL book “More QRP Power”. There were a few errors in the original QST article and although the parts list has been corrected in the “More QRP Power” reprint, the schematic hasn’t. For the record, when you look at the schematic, R17 should be labelled R7, C22 should be 0.01uF,  C19 (the capacitor connected between R15 and pin 5 of U2) should be 0.01uF, and “the other C19” – the capacitor connected between R16 and ground, should actually be labelled C20. If they’re going to reprint articles (which I’m very glad they do) I wish they’d make sure that all the corrections are included.

This was the first time I had ever attempted to fabricate an enclosure from PCB material and I’m quite pleased with the results.  I won’t fully detail my construction methods, as I got them from K7QO and WA4MNT, and they both already have excellent tutorials available online on how to make PCB cases. Ken WA4MNT’s PDF tutorial is here, and Chuck K7QO’s is here (Chuck’s tutorial has since disappeared from this url and I haven’t been able to find it’s new home, if it has one).

One or two people have asked me how I cut PCB material. If you don’t have a bench shear you can get nice clean cuts by scoring it with a utility blade and breaking it.  After using a sharp pencil to accurately mark the line where I want to cut, I use a metal rule and fresh sharp utility blade to make deep scores on both sides of the board. Expect to go through a few blades, and don’t be shy about replacing them;  cutting with a nice new blade is a pleasure, while an old one will just give you grief and raggedy cuts. Make sure that the cuts on each side are exactly opposite each other. Then sandwich the board in a vice between 2 bits of wood at the score mark thus:

Then, bearing down hard on the whole sandwich, firmly flex the board up and down until it breaks cleanly off.  You can run the board back and forth a few times over a piece of sandpaper, sandcloth etc. on a flat surface to smooth it a little, and you’re done. Easy! If you have a vice, you can use it for the above step.

Work progressed on cutting the panels for the enclosure (the 2 triangular pieces were used later to strengthen the cover) –

and before long I had a drilled front panel, a back panel, a base and 2 strengthening side-struts, which cleaned up with a scotch-brite pad and a little dish soap (for de-greasing). I made sure to rub the Scotch-Brite pad on the board mainly in straight lines as it does give the copper-clad a slight brushed look:

As suggested by WA4MNT in his tutorial, I used an angle iron to ensure 90 degree corners. The one I’m using is actually aluminum angle stock.  One thing that I would have had to learn the hard way were it not for this tutorial is the fact that when you solder the pieces of board together, as the solder cools, it shrinks, and you end up with something closer to 88 or 89 degree corners.  That can really mess up your nice square box, but Ken tells you how to square up your angles. Little by little the enclosure took shape and the thought occurred to me “Wow, I can actually do this!”:

I gave the finished enclosure a final cleaning with Tarn-X and sprayed it with a light coating of lacquer to prevent against oxidation of the copper. It didn’t fully work, as you can see from pictures of the completed receiver at the end of this post.  I’m thinking that I didn’t apply a thick enough coat of lacquer.

I thought it would be fun to fit the controls and stick-on feet to the enclosure to get a feel for what the finished receiver was going to look like:

I have a fondness for quality multi-turn wirewound pots, in the same way that I used to like using high quality air-spaced variable capacitors in my projects. Similarly,  the way that a regular one-turn pot feels when operating is important to me. The pot that I originally was going to use for the AF gain felt a little “scratchy” in the way it rotated, so I bought one from Radio Shack that feels silky smooth.  Even the first BNC connector that I used for the antenna socket (which was left over from an earlier project) was a cheap component, and I noticed that plugging and unplugging the antenna took more force and fiddling than it should have, so I used a new higher quality part (Mouser # 161-9323).  If this seems like a little too much attention to detail, let me explain. The connectors and controls are the way that you, the operator,  interface with the radio.  Higher quality components used here will greatly improve your experience of the radio. What would you rather use – a radio that takes force and fumbling to connect the antenna, has hard to adjust tuning due to the use of a cheaper one-turn pot, and a volume control that turns roughly, or a radio with controls and connectors that operate and rotate smoothly? These kind of things make a big difference. It might seem illogical to spend so much more on connectors and controls than on the rest of the circuit, but given how positively they can impact the user experience, it’s an investment worth making. I was hoping that this receiver would become a permanent part of my station, so spending a little more wasn’t a problem.

You’ll notice in the next picture that I used two 10-turn pots. One was for the tuning, and the other for regeneration. In the QST article, N1BYT details his method of using a one-turn pot with a separate preset to set the regeneration range on the main regen control. I’m sure that this works very well, but I happened to have an extra 10-turn pot available and was wanting an excuse to use as many of these wonderful things as possible, so I omitted the preset (R6 in the article) and used a 10-turn for the regen control. You do get a “whizzing” sound when adjusting the regen if you use a wirewound. To eliminate this, you can bypass between the wiper and ground for both audio and RF with a 10uF and 0.1uF connected in parallel. I’ve left mine as is for the time being, as I quite like the whizzing sound! (Edit: The novelty of the whizzing sound wore off swiftly, so I placed a 33uF cap between wiper and ground at the regen pot. It took care of things nicely.)

Daniel N1BYT’s original design for the WBR didn’t use a volume pot in front of the LM386, relying just on the 1K RF attenuation pot in the antenna lead. I decided that I wanted a little more audio gain in order to drive a loudspeaker, so I used the audio chain from N1BYT’s OCR II receiver, but connected a 10uF electrolytic between pins 1 and 8 of U2 to get the maximum gain of 200 out of the LM386 IC. Running the LM386 with maximum gain, and also fed with a preamp, I wanted to be able to control the gain of the AF stage as well as being able to attenuate the RF input, hence the extra pot. The toggle switch will be used to switch audio filtering at a later stage.

The enclosure build had gone so well that I started hoping that the performance of the receiver, when I built it, would be good enough to justify putting so much time and effort into the case. In retrospect, I probably should have built and tested the circuit first before deciding whether it was worthy of an enclosure.  Luckily it was.

I built the circuit Manhattan style using pads from W1REX at QRPMe.  I talked about the MeSQUARES in an earlier post and liked them so much that I ordered a sheet of MePADS from Rex.  MePADs are Manhattan pads for IC’s, as you can see in this picture. I had already broken off the pad I was going to use in this project:

As you’re building with these pads, if you find that you’ve glued one in the wrong place (I use Super Glue in the gel form), just slip a sharp utility blade underneath the pad and it comes right off. No need to fear a bad circuit layout, as you can change it if you make a wrong move.

The first part of the circuit to be built was the detector and regeneration circuit.  I didn’t have an MV104 dual tuning diode as specified in the original article, so used two back to back MV209’s, which you can see in the following picture, along with Q1 and Q2, the 2N3904 regeneration transistor and the MPF102 regenerative detector respectively:

Now I’ve added a few more components, including the 78L05 voltage regulator, which is hiding behind the grey 2.2uF electrolytic in the foreground:

The completed circuit. At this point, I hadn’t added the 10uF electrolytic between pins 1 and 8 of U2 (LM386).  The 2N3904 audio preamp is just below the LM386 audio IC:

Some more views of the completed circuit.  I knew that I was giving myself plenty of space to work with, but didn’t realize that there would be so much of it left over.  This is rather handy though, as it allows room for some low-pass audio filtering that I want to add later:

All very well and good, but would it work, and how well? The next picture shows the board installed in the case.  I added a 10K trimpot in place of R12 in order to adjust the tuning coverage of R11, the main tuning potentiometer. You can see the orange trim-pot near the front left-hand side of the board. It was only just now looking at this picture, that I realized I had left out C22, the 0.1uF capacitor in the antenna lead:

The same shot from a slightly higher angle:

By adjusting trimmer capacitor C8 and the trimmer resistor in place of R12, I achieved coverage of approximately 6970 – 7311 KHz. The extra 11KHz at the top of the band was important to me so that I can listen to the BBC World Service on 7310.  Vatican Radio broadcasts in English daily at 0250 utc on 7305, so the extra coverage above the top end of 40 allows me to receive that also.  Adjust C8 to set the top end of your coverage, and the trimmer in place of R12 to set the bottom end of the coverage. The tuning rate is a bit higher at the bottom end of the band than the top, being about 50KHz/turn in the CW sub-section.

I spent a few days enjoying the radio in this state before making a top cover for it.  The RF attenuation control doesn’t take the input signal completely down to zero. No doubt this has a lot to do with my decision to use an unshielded piece of copper wire to connect the antenna socket at the back of the rig with the 1K pot.  N1BYT does this in his receiver pictured in the QST article.  I liked it because it’s a reminder of the days when complete radios were wired using this technique, but I think I’ll probably replace that wire with a length of co-ax (after fitting C22 inline with the antenna lead) from the BNC to the 1K pot. That should allow attenuation of the input down to zero (or very close).  (Edit:  I just did, and it does.)

A top cover for the receiver:

The completed WBR Receiver (darn those front-panel fingerprints!) –

The space left at the top right-hand side of the front panel was in case I found a way to hook up a frequency counter to the regenerative detector while in oscillation in order to provide a frequency readout.  I have heard of people achieving this with the WBR by placing a pick-up coil near the main tank coil.  Still not sure whether I’ll pursue this.

Some of the things I’ve heard on this wonderful little radio in the first few days of owning it are the Vatican Radio transmitter in Sackville, New Brunswick on 7305 and Radio Australia (it was great hearing their Waltzing Matilda sign-on melody).  I also heard FO8RZ in French Polynesia on 7001 and immediately switched over to the Norcal 2N2/40 to work him with 4 watts! One of the reasons for building this receiver was in order to listen for AM activity on 40 (amateur, as we all know that there is plenty of broadcast activity there!) and I was happy this morning to hear W6LHQ running 200W of AM from his QTH in Modesto, CA on 7293KHz. This is one great thing about a regenerative detector – it will receive SSB and CW as well as AM. I believe it can receive FM too via the slope detection method, though I haven’t had a chance to try this out.

The Wheatstone bridge circuit in the tank is an elegant way to resolve the problem of oscillator radiation from the antenna that is common in simple regens, without resorting to adding a stage of RF preamplification, and it works very well.  I made no particular effort to match C5 and C6, so either I was lucky, or the circuit is forgiving, because I have encountered no issues with re-radiation. Without re-iterating the summary of this receiver’s performance that I gave in the second part of the 4th paragraph of this write-up I’ll just say this; I was hoping that this regen’s performance would be good enough for me to have it as a permanent part of my station, and it is.

The next step will be to replace the antenna input wire with a length of co-ax, and then build some audio filtering.  At that point, I’ll make some recordings of the audio and post a YouTube video.

I’m also thinking about bread-boarding another version of this receiver to encompass a larger portion of the shortwave spectrum. I have some MV108 varactors, and am thinking that the wider capacitance swing of one of those could give me broad coverage of a large part of the HF spectrum, with a fine tuning control provided by another diode. It would be great to have a regen to give me continuous  coverage of, say, 3 – 10MHz, or even higher.

Lots of fun and experimentation to come. Many thanks to N1BYT for this fine little receiver.

Notes added after above post was written – 

*Current consumption is low too – I measured around 12-13mA in regular use.

*A number of other builders have experienced problems with low sensitivity with their WBR’s.  LA3ZA found that substituting a 0.22uH inductor for Z1, the 1″ length of stiff wire between the center-tap of the coil and the ground plane, did the trick.  In the QRP-tech group on Yahoo, Steve AA7U did some experimenting and found 1uH was the optimum value for him.  Other builders have not had these issues with theirs.  My suggestion would be to build it as in the original design, adding the inductor if it seems necessary.

*As mentioned earlier, I added an audio pre-amp stage to my WBR, as suggested by N1BYT in the original article.  The schematic of the simple stage I added can be seen in this post.

*If I were building this again, I would change the configuration of the LM386 amp stage. Using a 10uF cap between pins 1 and 8 to get maximum gain introduces quite a lot of hiss.  The design that VK3YE used in the Micro 40 utilized a couple of ideas that had been discussed in SPRAT and is lower noise. I would try using the 2N3904 pre-amp as detailed in this post with the LM386 circuit as used in the Micro 40.

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