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!
28th March 2010 10:44
Whoops! One mistake on that schematic. The 1 meg resistor is supposed to go to the junction of the 100pf and 68k resistor on the gate of the lower fet! Sorry! I should have proof read!
28th March 2010 10:12
Alan, Ive included a link to the schematic of the detector/bfo. Sorry it took me so long to respond. I kind of forgot I posted here! I also built a 455KHZ SSB filter out of cheap ceramic resonators. Bandwidth is around 2.5khz. I will email the schematic as Im not sure how to post pictures here.
Link to schematic
http://tinypic.com/r/xvmn7/5
22nd December 2009 16:50
Doug,
Do you have a circuit diagram of that?
The cascode "infinite impedance" detector I've seen in a few places but I am yet to try it. As you say it would be easily amendable to LO injection as a product detector.
Regards,
Alan
21st December 2009 09:46
I came up with a design much like this one using cascade JFETs to emulate mosfets. I used an amplified AGC system and applied it to the 2nd "gate" of my home made mosfets. I also used an infinite impedance detector which could be easily turned into a product detector. This is a VERY quiet IF system.
26th June 2008 18:54
Curtis,
I've never had much luck with AGC in regens.
The regen-reflexive receiver has a bit of an AGC effect as its bias point is modulated by the recovered modulation envelope amplitude. It makes it much smoother to break into oscillation for detecting SSB, but it doesn't have the dynamic range needed for true AGC to compensate for variations in signal strength.
I tinkered with this circuit a bit a few days ago, adding a resistor in the emitter and controlling the device's bias point and gain more carefully. It improved the demodulated audio quality, but didn't improve the AGC range.
What you suggest sounds plausible in principle, you could use a dual-gate FET or a pair of JFETs in cascode to give you pretty good control, but there is no reason why it wouldn't work to some degree with just pulling the gate down. The regen control might be the source resistor with a Hartley oscillator topology, or the AGC line might bias the bottom of the regen pot and pull it below ground. I'll have to give it a try!
Regards,
Alan
26th June 2008 04:12
Hi, Alan.
I have run across your experimental circuit with AGC, and I would like know if this circuit will work in the tuned rf stage of a regenerative radio receiver. (Note: The AGC circuit is placed between the cold side of the antenna coil in the tuned RF stage at the radio's input and the output of the audio preamplifier stage of the radio.)
1st April 2013 22:07
peter wrote...