Thanks, very, very interesting! @Francesco: don’t fear, I will keep the secret… 😄
> Il giorno 1 ott 2024, alle ore 05:45, Jacques Fortin <[email protected]> > ha scritto: > > Hello Giovanni, > > Noise reduction of an amplitude-modulated signal by a product demodulator vs > an envelope detector is a verifiable fact. > I have found many explanations for this, but I believe that the thread from > the following shortcut will provide a valid answer to your question: > https://www.edaboard.com/threads/envelope-dectector-vs-product-modulator.262958/ > > For the R-390 and R-390A cases, the AGC system action time needs to be > "speeded up" when SSB is received, without changing the global AGC behavior > VS the AM case. > In other words, we need to keep the same AGC characteristic for both, because > the global receiver behavior and the signal meter calibration depends on it. > Many attempts were made up to now (and by many people) to "improve" the AGC > system of these receivers and the search for the best solution continues. > Some already available solutions uses external "add-on" circuitry to achieve > the necessary goals, but simultaneously implies some compromises vs other > receiver features, like the use of the MGC mode and the Noise Limiter circuit > when the product detector is activated. > What we try to develop for some time is a self-contained solution with no > "compromises"... > In that respect, I still have some (more or less simple) AGC circuits to try. > Larry Haney, on his side, have put many efforts on improving the tube-based > product demodulator using a 6BY6 that replaces the 6BA6 BFO oscillator. > What we usually call a "Lee" product demodulator. > And he is actually testing a noise limiter circuit compatible to both AM and > SSB reception modes. > Maybe someday we will combine all of our circuits together. > > Stay tuned... > > 73, Jacques, VE2JFE in Montreal > > -----Message d'origine----- > De : [email protected] <[email protected]> De la part > de Ing. Giovanni Becattini via R-390 > Envoyé : 30 septembre 2024 18:10 > À : Larry Haney <[email protected]> > Cc : R-390 Forum <[email protected]> > Objet : Re: [R-390] Tuning SSB > > Hi & Thanks. > > "Another important 'feature' of using a product detector is its natural > reduction of interfering noise coming in on your antenna. The amount of > noise reduction depends on the type of noise it is, but can be from 40% to > 75%.” > > Would you please explain to me why it reduces the noise? Because the BFO > signal returns back? > > ______________________________________________________________ R-390 mailing list Home: http://mailman.qth.net/mailman/listinfo/r-390 Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
