The type and specs of the AGC circuit plays a major role in SSB
demodulation...
I'm not too familar with the 51J4 AGC circuit but some of you are...
I had an R-390 that already had a 6BE6 product detector with wiring and
switching very similar to the Lee circuit. I had to add a small relay to
switch diodes in and out when the BFO was selected on the front panel...
It worked quite well and allowed excellent Exalted Carrier reception of low
power tropical AM broadcast stations on the low bands and did well for SSB
with the diodes added to the AGC ckt...
73...Jordan VE6ZT
----- Original Message -----
From: "Bob Camp" <[email protected]>
To: "Ing. Giovanni Becattini" <[email protected]>
Cc: "R-390 Mailing List" <[email protected]>
Sent: Sunday, September 29, 2024 3:18 PM
Subject: Re: [R-390] Tuning SSB
Hi
A BFO is not typically set up to provide great audio. A “product detector”
is optimized for lower audio distortion. Yes, there are other differences,
but they get into the “how did they do it” side of things.
The R390 came out before SSB was “a thing to use”. Even the 390A was right
at the start of SSB being something the military was looking at. Move a
few years down the road and the designs did have a “can do SSB” check box
on the design requirements.
Bob
On Sep 29, 2024, at 4:50 PM, Ing. Giovanni Becattini via R-390
<[email protected]> wrote:
Hi,
I don’t answer …because I “know", but just because I find the theme
intriguing and have similar doubts. This is a picture from the 51J-4
manual, which I think should be good also for the R-390A:
<Screenshot 2024-09-29 alle 22.11.58.png>
Because we must rebuild something similar to an AM signal but with just
one side band, I believe we must keep the BFO 1.5 kHz above the center
frequency of the filter for LSB and below for USB. And, obviously, we
need to “move” the received signal (upper or lower band) to stay centered
on the filter using the VFO.
In other words: tune the VFO so that the band (upper or lower) is
centered on the filter, and move the BFO +1.5 kHz above if the band we
want to read is the lower, and vice versa.
<What is SSB: Single Sideband Mo dulation » Electronics Notes.png>
This interpretation seems to be confirmed by the manual itself:
<Screenshot 2024-09-29 alle 22.21.53.png>
And this should be true also for SSB. In addition, it lets me think that
with the 6 kHz filter, the dial reading does correspond to the carrier
frequency of station.
All that assumes that the filter is centered on the IF channel, even if
not specified by the 51J-4 manual (left), but specified by the R-390A
manual (right)) and however rather obvious
<Immagineallegata-1.png><Immagineallegata-2.png>
I am not sure that I am not saying something wrong, so I hope that some
true expert can help us to clarify the things….
Gianni
Il giorno 29 set 2024, alle ore 19:29, Barry Scott
<[email protected]> ha scritto:
I hope I'm not opening a can of worms but I have some questions about
tuning SSB signals with the R-390/URR.
I know it works best if the LOCAL or LINE GAIN control is at maximum and
to
adjust the RF GAIN for a comfortable audio level. What I'm wondering is
what the proper way is to set the BFO.
I've always set it +1 for LSB and -1 for USB but I can also just leave
that
at zero and am still able to tune either sideband and now I'm wondering
if
setting the BFO + or - is mainly to get the dial to reflect the received
frequency. Is that an over-simplification?
I'm asking because I'm never really sure what the transmitted frequency
is. If I set the BFO + or -, it's only a matter of how I determine what
sounds good (e.g. no Donald Duck, etc.) as to what the dial reads.
I apologize if that's something that should be more obvious but reading
up
on it on the web doesn't quite make full sense to me. The discussions
seem
to revolve around whether the signal is in the IF's passband, etc., but
like I said, it seems I'm centering the signal in the IF even if I keep
the
BFO at 0.
Thanks for any insight on this,
Barry - N4BUQ
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