[R-390] Tuning SSB

Barry Scott 72volkswagon at gmail.com
Mon Sep 30 10:36:33 EDT 2024


Regarding the "original" two-diode mod, is that something that is supposed
to be in-circuit all the time or should those be switched out for AM and CW?

Thanks,
Barry - N4BUQ


On Mon, Sep 30, 2024 at 3:25 AM Larry Haney <larry41gm2 at gmail.com> wrote:

> As already noted, easy clear SSB reception on a 390 needs changes in 2
> areas: 1. AGC operation and 2. BFO injection level into the 'envelope'
> detector.  I've done both and have had very good success, but for good weak
> low signal level SSB reception, a 'product' detector is required (mainly
> due to the much lower noise level in it compared to an 'envelope'
> detector).  And then with 'product' detectors there is quite a range of
> noise levels in different designs and implementations.  The 6be6 method is
> ok, but there are better (lower noise) choices.  See my doc on our
> website: Improving
> Lee Prod Det and SSB AGC.pdf
> <https://www.r-390a.net/Improving%20Lee%20Prod%20Det%20and%20SSB%20AGC.pdf
> >.
> It has a link to this doc: R390A Fix Lankford 2 diode SSB AGC.pdf, which
> has an improved AGC circuit for much improved SSB reception.
>
> 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%.  I'm currently working on a circuit to allow correct use of the built
> in AM noise limiter circuit (designed by Jacques Fortin) to reduce most of
> the rest of it.  I'm in the final testing stage and it looks very
> promising.
>
> Regards, Larry
>
>
> On Sun, Sep 29, 2024 at 2:32 PM Jordan Arndt <Outposter30 at shaw.ca> wrote:
>
> > 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" <kb8tq at n1k.org>
> > To: "Ing. Giovanni Becattini" <giovanni.becattini at icloud.com>
> > Cc: "R-390 Mailing List" <r-390 at mailman.qth.net>
> > 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
> > >> <r-390 at mailman.qth.net> 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
> > >>> <72volkswagon at gmail.com> 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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