Comments for "Fremodyne VHF AM/FM Receiver"

16th August 2010 15:37

Alan Yates wrote...


I am glad you found my article about this. Thanks again for your website, it inspired me to play around with the Fremodyne (and the pulse-counting detector which I have not documented yet).

No, I have not measured its sensitivity. I suspect I would need to shield it properly to do so. I live in a strong signal area, but it still sounds quite a bit more sensitive than how you describe the vacuum tube versions.

Phase-locking the quench to the pilot is something I have long thought about. I have yet to conceive an easy way to do it without ruining the minimalism of the super-regen, which defeats the purpose beyond just performing the experiment to see if it does effectively remove the problem.

I do think this particular Fremodyne would benefit from external quenching. It would vastly reduce the quench variability with signal strength. Performing the quench with a bit of logic would allow extraction of the (log) signal strength and could facilitate experiments in phase-locking to the pilot. I have a sketch for doing it with just a quad Schmitt NAND but a microcontroller would be easier to experiment with.



2nd August 2010 14:20

John Hunter wrote...

Hi Alan,

I've often thought of converting the 12AT7 Fremodyne to a two transistor equivalent.

You've beat me to it! A very interesting article and it seems like a solid state version is quite practical from your results.

Have you attempted to measure sensitivity? I get the impression your circuit is more sensitive than the valve version which does require an aerial to receive anything, and needs about 100uV to provide a noise free output.

That dreaded MPX always gets in the way of FM super regen sets, but with the valve Fremodynes I've found once the quench frequency is set there's no need to adjust it. It does sound like you might be experiencing more of a problem than the valve version with this. It might be possible to improve on this by changing the quench waveform since this has the greatest bearing on receiver performance more than anything.

Perhaps the only way to truly eliminate MPX interference is to actually phase lock the quench oscillator to the 19KHz pilot tone to get rid of the beat.

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