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Tuesday, November 12, 2019

Listen to the ET-2's Minimalist Regen Receiver

I'm guessing that most of you have never listened to a regen receiver that uses only one transistor.  So in these videos I've tried to capture the experience.  The audio that you hear from the receiver is from a small I-phone microphone taped to the one of the headphones on my DLR WWII headphones.  So you are hearing it just as I hear it -- with no additional amplification. 

Here is N0WVA's schematic.  When I tune the "regeneration" control I am turning the knob on the variometer.  The broad or "bandset" tuning control is essentially N0WVA's 25 pf cap.  My fine tuning control (the one that I use the most in the video) is the equivalent of the smaller cap in parallel with the larger tuning cap. 

I had trouble shooting the video for this post -- taping the mic to the headphone turned out to be a bit difficult.  So I ended up with a few extra (and imperfect) videos.  I include them here for anyone who might want to listen some more to a single transistor regen.  (I have a few more -- let me know if you'd like to see them!)

In the next one, at the end I throw the switch to transmit allowing you to hear what "sidetone" sounds like on the ET-2


  1. Thanks for posting the demo, I'm impressed! Good to hear after listening about it in the podcast. 73 de Walter, AC4IM... still in Italy at the San Vito solar observatory.

  2. I was wondering what you were using for the sidetone. I see it is the "receiver blocking" method. :)

    Spotting your transmit signal is probably the largest hurdle to overcome with a regen. It may be possible with total shielding and clean antenna switching, but that takes away from the nostalgia of an open air station. Could you imagine doing this without crystal control? Imagine basically four free running oscillators all trying to stay close to each others frequency as the table vibrated and power supply voltage ramped up and down. Dont breath on the tank circuit!

    Doug N0WVA

  3. I Love your minimalist leanings, and CW. FB! Keep soldering! Ed KC8SBV

  4. Re Anon, there are techniques that don't require you to spot your tx signal on a regen. For example you could have a second tx crystal with its frequency shifted 800 Hz (eg VXO) from the crystal in the tx. That second tx crystal could be in an oscillator running all the time to provide a BFO for the regen rx. The regen rx would be brought to the point of oscillation but not oscillating. There's some 1930s(?) QST articles about the merits of a separate BFO for regens.

    Alternative you could configure your tx so the local osc is running all the time and have that as your BFO for the rx. But you will need to shift it 800 Hz to get an offset. That could even be done manually eg with a variable capacitor in series (and an inductor if you want more VXO range).

  5. Another thing that could be useful is putting a tx crystal in the antenna lead of the regen - that will act as a crude xtal filter. You might hear an interesting change in noise as you adjust the rx to near that frequency.

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