KD7KAR’s 40M Regenerative Receiver

For the second time since I’ve been active on CW (about 18 months) I had a QSO today with a station who revealed that he was receiving me on a regenerative receiver. This was a first in a way, because the last time was with W7QQQ whose regen receiver uses a tube.  KD7KAR’s receiver uses an MPF102, so this represented the first time I’ve been in QSO with a station that was using a solid state regen receiver to receive my CW sigs.

As a teenager in England, and eager reader of RadCom (the RSGB publication) and Practical Wireless, I remember seeing circuits of simple regenerative receivers employing FET’s and wondering how they performed on the ham bands. I did own a one tube shortwave regen receiver when I was about 16 or 17 called the HAC (short for “Heard All Continents”). I used it a few times to listen to amateurs but didn’t think of it as a serious receiver for amateur work. The tuning was a bit coarse, so that didn’t help.  I know that regens were very popular with hams before the onset of the superhet but find it interesting that they can still be used effectively today.

They certainly are effective.  Rob KD7KAR gave my 5 watt signal a 579. My 5 watts traveled 400 miles and were detected by his MPF102 regen receiver.  It was a design by Doug De Maw W1FB.  Pretty impressive.  He was also using a 10 watt (also homebrew) crystal controlled transmitter, which was crystalled up for 7030KHz. He did comment that being rockbound was a bit limiting, but if you’re going to be rockbound on 40M, 7030 is a good place to be.  I have full VFO control and still spend much of my time on 7030 anyway. One thing about regens – Rob said that he has to tune it with a broomstick handle! For anyone who has not used a regen receiver, they can be very sensitive to hand-capacitance effects.

Wish I had a picture of Rob’s set-up to post here.  Perhaps if Rob sees this post he’ll be able to help out.

Every QSO is different. Some are memorable because of the distance, or the rarity of the location contacted, others are memorable for the quality of the conversation or some other type of human interest.  This QSO fell into the latter category. Also, every QSO I’ve been having recently makes me think of how much more fun it will be when I’m beta testing the new CC-40 transceiver from etherkit and can report to the other station that I’m running a yet-to-be-released brand new QRP TX/RX for 40M.  It’s going to be fun having the CC-40 PCB sitting on the bench in QSO:

“Rig hr is CC40 BT Pwr 2W 2W to inverted vee at 47ft”.

Brilliant. Can’t wait.

Thanks for the QSO KD7KAR – and loved hearing about your home-brew station!


8 thoughts on “KD7KAR’s 40M Regenerative Receiver

  1. Oddly enough, I’ve been smitten a bit by the regen bug lately. If I had any free time, I’d try to build one. I have been checking out YouTube videos of homebrew regens in action, especially tube valve-constructed receivers. The fidelity listening to a good AMBC or SWBC station is something that you just can’t get with your modern production general purpose RX.

    I gotta tell you…I was already pretty psyched to get the CC-Series in production, but I think your excitement has just about doubled my anticipation!

    Jason NT7S

  2. Ha – good modification with the tube/valve nomenclature! When I took the exam for my license back in 1978, I took the very last exam in the UK that required the answers to be written out in full, essay-style. It was also the last exam to allow valves to be used in the schematics. I filled the pages up with schematics of local oscillators, mixers, amps and anything else they asked for – all utilizing valves. It was glorious! I passed with high marks.

    Yes, I’m really into this Jason. I haven’t figured out whether I’m going to put it in an enclosure, or make an open chassis from PC board, or attempt some other kind of box. I’m planning on getting the board finished within a few days after receiving it and hoping to have it on the air pretty soon *fingers crossed* so that I can be making QSO’s with it. I don’t ever rush building things – like to take my time and make sure I’ve got things right, as well as enjoy the build and the opportunities for lots of leisurely cups of coffee with 40M playing in the background. I’m hoping to get some good pictures of the build also.

    I see a CC-40 to CC-40 QSO in the air very soon *stares into crystal ball*.

  3. Nice posting, Dave. It makes me “re-realize” what an amazing hobby we have. Our tickets are a license to experiment and try new things – even if the new thing is an old thing! Do you have a rough date as to when you may be airing that CC-40? I’ll definitely be listening for you…

  4. There is so much in this hobby to keep us occupied isn’t there John? I’m finding plenty to occupy me just in working on my CW speed and operating techniques. My goal is to become fully fluent and conversational so that I can run a QSK ragchew at 25 wpm. Then there’s the building side of things. Great fun.

    Not sure what the timeline is John – Jason just got the beta boards back and is building the first one now as we speak, then he has to work on a preliminary set of instructions before sending a package my way. It’s funny, because after building the 2N2/40 and the Tut80 I felt that I didn’t need another QRP TX/RX, but this one has caught my interest. My guess would be that perhaps I’ll be on the air with it in 2-3 weeks, based on what Jason’s told me. He should be on the air with his in a matter of days though, so I’ll definitely be listening on 7030 for NT7S in the very near future.

  5. Dave,
    I remembered you mentioned you had a blog, and was surprised to see our recent QSO featured! It was great fun to QSO with the homebrew xcvr and xmtr. Your 5 watt signal was coming in fine. Must be some new sunspots. My return to homebrewing was precipitated by reading SOLDERSMOKE, by Bill Meara N2CQR. It’s got lots of interesting stories, and features some good explanations of technical subjects, like mixers and transistors. Maybe I’ll have my VFO working when we QSO again. The xtal is nice and stable, but lately there have been pileups from 7028 to 7035, which makes it impossible to CQ. I’m still very pleased to have the keyer working now, so I don’t have “glass arm” issues, and can use the paddles to keep up if necessary. Hope to CU agn soon.
    KD7KAR Rob

  6. Rob – I’ve been meaning to e-mail you and thank you for the QSO, as well as give you the link to this blog post, so I’m glad you found it. It was a real thrill to imagine my signals making it into your homebrew regen receiver – reminded me of all the schematics I’d seen of regens using various different FET’s when I was a kid and wondering how they worked.

    The pile-up you mentioned, for VP8ORK, is happening right now on 40 as I sit typing this.

    73 and I hope to work you with the new etherkit CC-40 when I’ve finished building the beta kit in a few weeks. I’ll look out for you.

  7. > One thing about regens – Rob said that he has to tune it with a broomstick handle! For anyone who has not used a regen receiver, they are very sensitive to hand-capacitance effects.

    Sure — if they’re not properly shielded and buffered from their antennas. If hams built L-C transmitter VFOs as casually as some build regens, broom handles, wobbles and RF feedback would be a way of life. Just because a receiver is simple doesn’t mean it has be built like the Great Depression is still on. All of my homemade receivers currently use regenerative detectors–some at signal frequency, most at IF–and in 45+ years of experimenting with such radios I have yet to encounter hand capacitance. One thing I insist on: Design the radio use a 50-ohm antenna system. Implementing a regen’s “antenna system” by lightly coupling a random hunk of wire directly to the detector tuned circuit is Step 1 of a journey in the wrong direction.

    Best regards, Dave
    amateur radio W9BRD

    1. I changed the wording to “they can be very sensitive to hand-capacitance effects”. Thank you for bringing this up, David.

      In the 4 years since writing this post I have built 4 regens, all of which have been remarkably stable. I do spend a lot of time thinking about physical layout and enclosures though. I would have to agree with your statements. I believe that Rob’s regen was fairly minimal in terms of the enclosure.

      One of the best pieces of advice I have heard on building regens is to build ’em as if you’re building a VFO!


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