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Author Topic: Got my Single-Signal Reception working .. thank you all!  (Read 571 times)
KC9KEP
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Posts: 208


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« on: August 15, 2011, 06:44:51 PM »

Re: my earlier post “Help understanding single-signal reception via i.f. regeneration, please ..”, I believe that I have the circuit functioning now!

As per the 1941 ARRL handbook instructions, I aligned the i.f. strip by removing the antenna-tank and local oscillator plug-in coils.  Then, I insured that the BFO was OFF and applied a 455 kH (1-kHz AM modulated) test signal across the input tank capacitor.  Using a scope and monitoring the audio output from the (second) detector, it was a simple task to align the i.f. coils.  It required a few iterations to get them to fully peak.

Then I turned on the BFO.  I wanted the BFO to zero-beat with the applied 455 kHz in order to center the front panel BFO control at 12:00.  In this manner, I could rotate the BFO cw or ccw for a higher/lower BFO pitch than the i.f.  I could "see" the zero-beat on the scope with BFO turned "on" and the applied 455 kHz unmodulated.

Then, I put my antenna tank and local oscillator plug-in coils back into the set and connected the antenna.

I immediately noticed that the CW signal was much stronger on one side of zero-beat than the other.  As a matter of fact, the CW pitch became even louder as I tuned towards the zero-beat and located a sweet-spot where the CW/BFO tone seemed to resonate dramatically.

But, SSB signals had a problem:  The SSB signals were loudest on the “wrong-side-of-zero-beat” so I couldn’t “decode” them.

I don’t know what shifted, but I discovered that my BFO was no longer centered in its range with respect to the i.f.

An adjustment (by ear) of the BFO coil brought the front panel BFO control back to where I wanted it, no BFO beat at 12:00 and +/- pitch when turning the BFO control CW and CCW.

I could not actually measure the BFO frequency because any probe that I brought near the BFO output would pull the oscillator and detune it :-(

At any rate, this is pretty cool!  I’ve never operated or experienced such a set, so I was not certain what I was looking for ..  But, the Single-Signal effect does work quite well if one has the patience to dial it in carefully.

Copious thanks to all the help!

73

--KC9KEP
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G3RZP
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Posts: 4301




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« Reply #1 on: August 16, 2011, 01:37:36 AM »

Glad you got it going.

Interestingly, I know of 2 professional superhet receivers of the just pre WW2 era that used regeneration. One was a UK Army receiver, which was also used a lot in embassies, called the DST100. It was dual conversion, and had a separate 6J5 to give regeneration at RF, and also had some feedback in the IF. Another rx was the Marconi Marine CR300, the first superhet they produced for marine use prior to that, all Marconi marine receievrs were TRFs. That had 'controlled feedback' to adjust the IF selectivity, and was remarkably stable in that respect.
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