Shift in output levels on DUO

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MTG
Posts: 38
Joined: Sun Feb 12, 2017 6:07 pm

Shift in output levels on DUO

Post by MTG » Mon Oct 22, 2018 9:23 am

I am experiencing an issue that I raised with the SDRUno team a couple of years back with my RSP2 and was not resolved - I had to live withit :-( . I now have a Duo and am experiencing the same issue. I run my systems 24/7 and use a GPS disciplined oscillator as a level and frequency calibration. Below is what has happened to my calibation level over over a couple of days. This is output via Virtual Audio cables and reported with Spectrum Lab. The two channels are a split signal applied to each Duo tuner. The EXW AGC is set to 100. The RX Control panel meter readings have not changed.
Callevel.jpg
Callevel.jpg (74.85 KiB) Viewed 4145 times
The interesting thing here is that the two levels are drifting apart and SNR remained the same.
Any ideas where the problem is?

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MTG
Posts: 38
Joined: Sun Feb 12, 2017 6:07 pm

Re: Shift in output levels on DUO

Post by MTG » Tue Oct 23, 2018 3:17 pm

I don't seem able to edit the previous posting - I get a message saying that I have to answer at least to polling messages???

The problem is possibly/probably not SDRUno's so any clues about windows 7 or laptop sound that may cause the problem would be useful. A further jump downward occurred last night. At this rate I will be into Galactic noise levels by Christmas ;)
Callevel 0181023.jpg
Callevel 0181023.jpg (59.36 KiB) Viewed 4102 times
The difference between the two tuner outputs is increasing.

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Roger
Posts: 217
Joined: Fri Dec 29, 2017 7:59 pm

Re: Shift in output levels on DUO

Post by Roger » Tue Oct 23, 2018 4:22 pm

MTG,

Try recording with Audacity, instead of Spectrum lab, for a day or so and see if you get the same drops in level. That way you will know if Spectrum Lab is the problem.

Roger

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MTG
Posts: 38
Joined: Sun Feb 12, 2017 6:07 pm

Re: Shift in output levels on DUO

Post by MTG » Tue Oct 23, 2018 5:14 pm

BTW Can VACs connect to two different apps simultaneously? If so I could record both.

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MTG
Posts: 38
Joined: Sun Feb 12, 2017 6:07 pm

Re: Shift in output levels on DUO

Post by MTG » Wed Oct 24, 2018 3:11 pm

Roger - being a complete stranger to Audacity I have looked at the manual and am still do not understand what you are suggesting. I follow using Audacity instead of Spectrum Lab to eliminate the latter. Is the idea that I take a reading from the strip indicators for each channel that show signal levels from about -55dB and upwards and then check again every so often for changes? The problem is that the signals I have are below the -55dB minimum and do not show up. I don't want to change any settings as that may change the effect.

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Roger
Posts: 217
Joined: Fri Dec 29, 2017 7:59 pm

Re: Shift in output levels on DUO

Post by Roger » Thu Oct 25, 2018 5:49 pm

MTG wrote:Roger - being a complete stranger to Audacity I have looked at the manual and am still do not understand what you are suggesting. I follow using Audacity instead of Spectrum Lab to eliminate the latter. Is the idea that I take a reading from the strip indicators for each channel that show signal levels from about -55dB and upwards and then check again every so often for changes? The problem is that the signals I have are below the -55dB minimum and do not show up. I don't want to change any settings as that may change the effect.
You posted in another thread that your maximum signal range was 55 dB ( -15 and + 40 dB of the calibration level). If your signals are below the 55 dB minimum they are too low out of the Virtual Audio cable or you have not set the record volume in Audacity to maximum (1). If the recorded level is too low in Audacity you can use the Amplify function (under Effects) to scale all the values up by xx dB. Just use CTL-A to select all of the recorded data, click Effects- Amplify and it will tell you how much gain it will apply without clipping. After you click OK the strip recorder will be updated.

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MTG
Posts: 38
Joined: Sun Feb 12, 2017 6:07 pm

Re: Shift in output levels on DUO

Post by MTG » Mon Oct 29, 2018 12:33 pm

You suggested using Aaudacity to eliminate or otherwise any fault in Spectrum Lab. I was waiting until I had another shift before changing over from one app to the other (audacity) but the level has been stable for the 6 days. Holding off changes turns out to be the right decision. It was some time back that I had the original shift issues - it may have been as the equipment warmed up so I will check a turn off of the Duo tuners and try again. Does changing to "Stop" from "Play" turn power off on the Duo?

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MTG
Posts: 38
Joined: Sun Feb 12, 2017 6:07 pm

Re: Shift in output levels on DUO

Post by MTG » Tue Oct 30, 2018 4:57 pm

I have run a test using the same arrangements described above. In the plot below I show the changes in the Volume output level as monitored in two separate instances of Spectrum Lab and combined into the one plot. The RSPDuo is being controlled by SDRUno and the output is connected to Spectrum Lab by Virtual Audio Cables.
UnoDuoShiftTest10.jpg
UnoDuoShiftTest10.jpg (57.86 KiB) Viewed 3844 times
The plot starts with steady levels (around -72 and -75 dB) from the two tuners. At 11:50 the "STOP" button on both tuner instances were clicked. The VACs and Spectrum Lab were left untouched. When "PLAY" was activated again the levels have risen to around -50dB, soon drop to about - 55dB. After 5 minutes both levels drop further to -63 and -65 dB and stay steadt for the next 3 hours.

I have used Spectrum Lab and VACs for many years and have not encountered this problem with other SDRs, other than my original post on this Forum a few years back with RSP2 and the earlier version of SDRUno.

Should I raise this issue with the tech team because it does seem to be a problem with SDRPlay hardware or sortware?

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Roger
Posts: 217
Joined: Fri Dec 29, 2017 7:59 pm

Re: Shift in output levels on DUO

Post by Roger » Wed Oct 31, 2018 2:05 am

There is a problem with the AGC in SDRuno when you turn it off. Lets say you are running with AGC on and the gain level is set to 100 (the default). Now tune to an area where there is no activity and only noise is present. There will be considerable noise on the audio output because the AGC will have increased the gain to the maximum. If you turn off the AGC the output level of the noise should drop way down. BUT in SDRuno it does not do this. The noise level stays the same UNTIL you tune in a signal for a few seconds and then go back to noise gain. Once you have done this the noise level will be low on the audio output.

This is a bug IMHO....

The other thing you should check is that you have locked the fractional resampler in the output (see user manual for details0

I suggest that you try HDSDR and see how it works for your application where you don't want any AGC (II or audio). It is quite easy to use and in my testing the SSB output is more linear over a wider range than SDRuno.

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MTG
Posts: 38
Joined: Sun Feb 12, 2017 6:07 pm

Re: Shift in output levels on DUO

Post by MTG » Wed Oct 31, 2018 8:50 am

The plots are showing a calibration signal level and not noise levels. The signal was on the input to the RSPDuos continuously before, during and after the "Stop" - "Play" sequence. The level drops not only at the start but at other times and the calibration signal has not changed. There is also an antenna on the inputs and the background noise will naturally change. I was hoping to use the Uno - Duo kit for some radio astronomy applications where I will need to stop and start things during the experimental and set-up stages and clearly these changes are a BIG downside. The equipment is touted for scientific use but the supporting software is not quite up to it yet it seems ....

Are there any alternative SDRs for the DUo hardware?

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