RF Gain control on SDR-Console V3

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Max99
Posts: 6
Joined: Sun Jul 29, 2018 2:04 pm

RF Gain control on SDR-Console V3

Postby Max99 » Sun Jul 29, 2018 2:38 pm

Apologies if this has been asked before but searched and cannot find as the bulk of users here seem to use SDR Uno, so to be clear it's SDR-Console V3 I'm asking about, and receiver is SDRPlay RSP2Pro.

With no antenna connected to any input and with antenna switch select to Input A or B, IF gain set to manual -35dB, AGC 'off', and visual gain set to 'zero', adjustment of the 'RF Gain' control seems to work exactly the opposite way around to how it is labelled.

So, with above settings, when the RF slider is set to 0 (labelled 'max') the audible and visible noise floor is at minimum and on the pan display noise level is about S0, and with the slider set to 8 (labelled 'minimum') the noise floor shoots right up to around S7, and predictably in stages at every setting in between, 1 to 7, however there is a larger 3 S point jump up in noise between setting 7 and 8 than between the lower settings.

This would seem to indicate to me that position 0 (labelled 'max') is in fact minimum gain (or I would guess 'zero' gain as the noise floor is almost exactly on S0 on the pan display) and position 8 (labelled 'min') is in fact max pre-amp gain?

Can anyone from the SDRPlay design team please confirm is this correct? I asked on the SDR-Radio forum but nobody came back with the definitive answer including Simon Brown. At least one person was convinced it is the other way around, but I can't see how that can be so given the behaviour of the noise floor as described above with IF gain set to manual and no AGC?

Anyone know for sure?

Thanks, Max
Last edited by Max99 on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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SDRnerd
Posts: 43
Joined: Sun Jan 07, 2018 6:29 pm

Re: RF Gain control on SDR-Console V3

Postby SDRnerd » Mon Jul 30, 2018 12:01 pm

You can state your questions on the SDRconsole group which you can find here:

https://sdr-radio.groups.io/g/main/topics

Sometimes gain is mistaken by attenuation in some programs. I do not own a RSP2pro, but use a RSP1a and a RSPduo where this causes some confusion for some users. When you see the noise floor rising when changing the "gain" settings, this means that you raise the attenuation value. The highest gain (less attenuation) is when the noise floor is at its lowest value on the FFT and waterfall. After this is observed, connect your antenna and you must at least see your base noise increasing by 10 dB. If this is not so your antenna is not working well or there can be a problem with your feedline or connector.

I hope this is of some help to you.

Good luck :!:

Ron Liekens
ON2RON

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Max99
Posts: 6
Joined: Sun Jul 29, 2018 2:04 pm

Re: RF Gain control on SDR-Console V3

Postby Max99 » Wed Aug 01, 2018 12:04 am

Hello Ron

Thank you for your reply. I did post on SDR-Radio forum as mentioned but no definitive reply sadly.

I would be grateful if you could explain why the observed (and heard) noise floor rises with increased attenuation at the front end? My expectation would be that raising the gain in the front end (with no antenna connected) will be a source of greater noise and the reverse would be true. Is it because of some feature of the AGC in the intermediate stages? Remember I had the AGC off, and the IF gain set to 'manual'. I've never observed this behaviour in any of the analogue receivers I owned over the years. In general the audible noise always rises with the RF gain at max, and reduces greatly with the RF gain at minimum, so I'm very confused as to why this would be the opposite way around?

Any more technical detail in your explanation would be most appreciated as to me it is counter-intuitive!

Many thanks

Max
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Paul
Posts: 343
Joined: Fri Feb 17, 2017 9:52 am
Location: SW UK

Re: RF Gain control on SDR-Console V3

Postby Paul » Wed Aug 01, 2018 8:57 am

Your question and it's answers tend are obviously by knowledgeable persons in the radio field.
However, as a very "basic" user of and RSP2 and SDRuno (I have tried Consloe and HSDR, but uno suits me better), may I offer the following in case it has been obfscured by technicality.
The basic RF Gain/Attenuation setting in uno and presumably EXTIO versons of it is "ATTENUATION," thereffore MAX and MIN refer to attenuation and not gain, so MAX is maximum attenuation.
In un V1.23 it is so labelled - can't recall what it was previously.

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Max99
Posts: 6
Joined: Sun Jul 29, 2018 2:04 pm

Re: RF Gain control on SDR-Console V3

Postby Max99 » Wed Aug 01, 2018 10:51 am

Hi Paul

Thank you for your answer but my original question relates only to SDR-Console software, not Uno as I am not a lover of the Uno software (too many separate window instances for a start). I am aware from many other posts that the 'gain' control in Uno operates in the reverse sense and because the SDRPlay does not always behave logically (in an analogue sense) it's not so easy to diagnose exactly what it is doing, hence the question.

By logically, what I mean is that in an analogue receiver it is very obvious that when the RF gain control is increased the effect is clearly and linearly audible, but this is certainly not my experience with the SDRPlay. It seems that even with everything set as 'manual' as possible there is some auto-processing going on that masks the actual behaviour of the receiver.

73

Max
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