Posting Comment for "Fremodyne VHF AM/FM Receiver"

*Author Name
Email Address
Website URL

About Posting a Comment

Comments are moderated before they will appear on the website, this is a manual process and may take some time. Please be patient.

Author Name is a required field.

Email Address is optional, but without one I won't be able to contact you back. It is never shown or linked on the website. You can always just email me if you'd rather not post a public comment. I generally reply in-line with a comment rather than email you back, unless I want to discuss something in private or off topic. Please check back to see when I reply.

Website URL is optional, if supplied the Author Name will be hyperlinked to this URL.

You may use wikitext in the body, preview may be handy here. Don't worry if you can't figure them out, just give me a hint what you want linked to what and I'll do it during moderation. Wikitext is not BBcode!

Spammers: Please don't bother wasting your time scripting up posts to this form. Everything is moderated, your post will never be seen on the web even transiently, there is no way to even view it by its internal ID, it will never be indexed. I will simply delete your post in the moderation interface. If I'm your target audience you're really on the wrong track; I'll never click on a URL in your garbage. The post content is not emailed to me (and I don't use a Win32 mail client anyway), I view the posts in plain text in the moderation interface so no clever tricks of any kind will make anything you type be interpreted by anything other than me, a human. Just give up and go elsewhere please!

16th August 2010 15:37

Alan Yates wrote...

John,

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.

Regards,

Alan

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.