TheRadioBoard

hi all.
I want to ask if anybody implemented a variable coupling between RF amp and detector? Is it needed? what is the best way ? and so on.
Thanks

Are we talking about a regen set or a TRF or what?



If this is in a Regen set and the RF amp is providing the "isolation" in order to prevent the antenna Loading the detector, then NO the variable coupling is not needed!(not to prevent loading by the antenna)

If the purpose of the "variable coupling" is for the purpose of controlling bandwidth/selectivity(and not to prevent "loading") then maybe it is needed(or just desirable not actually needed).



Without knowing more about what you are trying to achieve, in what type of set, I cant really provide any other answers.

73
kb0lxy

It would certainly help to know the application and what you are trying to achieve. If it is a regen with RF buffer/amp then normally an attenuator is added at the RF stage input instead of variable RF stage to detector coupling.

Not a tube desgn, but here's a Charles Kitchin FET design that implements variable coupling of the RF stage to the detector.

http://www.arrl.org/files/file/Technolo ... hb1768.pdf

I believe Mr. Kitchin later said that while variable detector loading was the best approach for highest (potential) selectivity, this was very difficult to do properly because the physical presence of the variable loading capacitor and the wires will load down the detector. He proposes as an alternative light fixed coupling of RF amp to detector and variable RF attenuation ahead of the RF amp.

Here are some links where he discusses the issue:
http://groups.yahoo.com/group/regenrx/message/5402
http://www.archive.org/details/Updating ... veCircuits
http://www.archive.org/compress/Masscon ... eedingsiso

I am talking about regen receiver.
Thanks to all. The last post answers my question.