[R-390] Tuning SSB

[Ing. Giovanni Becattini]

Thanks, very, very interesting!

@Francesco: don’t fear, I will keep the secret… 😄

> Il giorno 1 ott 2024, alle ore 05:45, Jacques Fortin <jacques.f at videotron.ca> 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 : r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> De la part de Ing. Giovanni Becattini via R-390
> Envoyé : 30 septembre 2024 18:10
> À : Larry Haney <larry41gm2 at gmail.com>
> Cc : R-390 Forum <r-390 at mailman.qth.net>
> 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?
> 
>