[R-390] Tuning SSB

Larry Haney larry41gm2 at gmail.com
Mon Oct 7 14:04:49 EDT 2024 

Hi Francesco,  I've heard that the detector you reference can be a good low
'conversion' noise detector if the right diodes are used, but I don't know
anything else about it.

Regards, Larry

On Mon, Oct 7, 2024 at 4:36 AM <k5urg at yahoo.com> wrote:

> Larry, what you are suggesting may happen on a solid state double balanced
> mixer, where the diodes have a threshold voltage, but not in vacuum tube
> environment.  In reality, it doesn't happen, as the LO (BFO) is of high
> enough amplitude to force the diodes to conduct.
>
> There is extensive theory and math related to double balanced mixers
> (visit the Mini-circuits web site), and none of it shows noise reduction.
> The math is simple and doesn't show any noise reduction effect.
>
> Best, Francesco K5URG
>
> -----Original Message-----
> From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> On
> Behalf Of Larry Haney
> Sent: Monday, October 7, 2024 5:17 AM
> To: Ing. Giovanni Becattini <giovanni.becattini at icloud.com>
> Cc: R-390 Forum <r-390 at mailman.qth.net>
> Subject: Re: [R-390] Tuning SSB
>
> Hi Gianni,  In reference to your question as to why there will be less
> static type noise coming out of the product detector than an envelope
> detector, I've not been able to find an explanation from an engineering
> source, but Don Stoner writes in his book 'New Sideband Handbook' from 1958
> on page 191 in the Product Detectors section '.... there will be less
> interference since output can only occur when a signal beats with the bfo.'
>
> I believe that with the envelope detector with bfo injection there is no
> real limiting effect on what will pass through it, so all the noise on the
> IF output goes through.  Whereas with the product detector, having the bfo
> signal on the control grid has a very limiting effect on what passes
> through it.  So in a product detector, only some of the noise on the signal
> from the IF output will pass through.
>
> This matches what I see from the testing that I have done.
>
> Regards, Larry
>
>
> On Mon, Sep 30, 2024 at 3:10 PM Ing. Giovanni Becattini <
> giovanni.becattini at icloud.com> wrote:
>
> > 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?
> >
> >
> > Il giorno 30 set 2024, alle ore 10:24, Larry Haney
> > <larry41gm2 at gmail.com> ha scritto:
> >
> > 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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