[R-390] Tuning SSB
Ing. Giovanni Becattini
giovanni.becattini at icloud.com
Mon Oct 7 06:48:10 EDT 2024
Thank you very much. If the topic is not clear for you, you can guess for me 😁
Thanks again
> Il giorno 7 ott 2024, alle ore 12:16, Larry Haney <larry41gm2 at gmail.com> ha scritto:
>
> 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 <mailto: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 <mailto: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 <mailto: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 <mailto:kb8tq at n1k.org>>
>>>> To: "Ing. Giovanni Becattini" <giovanni.becattini at icloud.com <mailto:giovanni.becattini at icloud.com>>
>>>> Cc: "R-390 Mailing List" <r-390 at mailman.qth.net <mailto: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 <mailto: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 <mailto: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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