Constantly Changing Waterfall Contrast

[sunwave]

I am running SDR-Console Bete v3.3 build 3131 with the SDRPlay RSP1a. I have noticed that the waterfall contrast always changes. I don't know what causes this. The best way for me to illustrate this is by video.



Is there a way to stop contrast from always changing?

Thanks
sunwave
Oklahoma City, OK USA

[Simon G4ELI]

Hi,

My suggestion is that this is either background noise or more likely AGC, if AGC then you have some strong signals which are 'pumping' the AGC?

[Max]

I am running SDR-Console Bete v3.3 build 3131 with the SDRPlay RSP1a. I have noticed that the waterfall contrast always changes. I don't know what causes this. The best way for me to illustrate this is by video.

Is there a way to stop contrast from always changing?

If you look at the spectrum above the waterfall you will see that this is not the waterfall contrast changing. It's some sort of broadband noise source, most likely local to you, that keeps raising the noise level up and down.

Tune to a part of the band with no signals then listen and watch the spectrum display it the top half of the window (and the waterfall). It's the noise source you need to find and remedy.

If you select a wider sampling bandwidth (several MHz) and zoom right out you may see something, like a broad peak of some sort, relatively close in the spectrum that enables you to identify the source. Unfortunately the SDR Play receivers are not great in terms of front end selectivity, certainly the earlier models, and can be problematic in this way in being badly affected by large signals even a long way from the tuned frequency. I have one (RSP2Pro). I personally gave up with it on HF on a decent antenna. Still OKish for VHF/UHF. I think the RSP1a had some improvements over the RSP1 and RSP2. Not sure. You'd have to Google.

73

Max

[Max]

Hi,

My suggestion is that this is either background noise or more likely AGC, if AGC then you have some strong signals which are 'pumping' the AGC?

Yes, AGC pumping good point. Also just noticed they have RF gain set to 8. In my experience that's way too high on an RSP receiver. Those receivers have some silly amount of gain in the front end that overwhelms the later stages. So try winding the RF gain right down to perhaps in the range 0 to 4 in conjunction perhaps with also turning off the AGC. See how that helps.

73

Max

[sunwave]

Thanks for the replies. AGC pumping is the problem. I turned off AGC in the "Home" tab then it quit pumping.

I probably should have known not to use SDR-Console's AGC. It is noticeably too aggressive. Pumping is not noticeable using native software, SDRuno. I like SDR-Console better.

[Max]

Thanks for the replies. AGC pumping is the problem. I turned off AGC in the "Home" tab then it quit pumping.

I probably should have known not to use SDR-Console's AGC. It is noticeably too aggressive. Pumping is not noticeable using native software, SDRuno. I like SDR-Console better.

The AGC in the ribbon bar along with the radio settings, AFAIK (Simon may correct me) is the radio hardware AGC. I don't believe that will be anything to do with the software. Maybe SDR Uno operates a further AGC action later in the software chain that somehow levels the noise floor. That would simply be masking a deficiency on the hardware that SDRC does not attempt to cover up!

Agree about SDR Uno software. Poor GUI in anyone's book.

73

Max

[KA1GJU]

I get the same pattern on all my SDR's located at the QTH. It's an issue with the powerlines, insulators, or splices. When it drys out, such as the AM dew drying on the lines and such, the broadband noise comes and goes and leaves the same slight jump in noise floor for seconds at a time, then it clears. It repeats itself over and over with progressively longer times of elevated noise floor. Eventually it remains elevated until nightfall with dew or if it rains, it remains quiet.

In reference to the RSP1A, I have to run mine at 6 or 7 RF Gain, -30 or -35dB IF Gain Manual, and visual gain of 0 or 5 dB. But mine is on a 150' Inverted L, with a 9:1 unun and +300' of 1/2" Aluminum 75 ohm CATV hardline to a 4 port active multiplexer feeding 4 SDR's of various mfgs.

73 Kriss KA1GJU
Home of the KA1GJU Super Station SDRC Servers in NH, USA

[sunwave]

Thanks for the replies. AGC pumping is the problem. I turned off AGC in the "Home" tab then it quit pumping.

I probably should have known not to use SDR-Console's AGC. It is noticeably too aggressive. Pumping is not noticeable using native software, SDRuno. I like SDR-Console better.

The AGC in the ribbon bar along with the radio settings, AFAIK (Simon may correct me) is the radio hardware AGC. I don't believe that will be anything to do with the software. Maybe SDR Uno operates a further AGC action later in the software chain that somehow levels the noise floor. That would simply be masking a deficiency on the hardware that SDRC does not attempt to cover up!

Agree about SDR Uno software. Poor GUI in anyone's book.

73

Max

SDRPlay doesn't mask it in SDRuno. The software shows the overall gain reduction values in the main window. If you ever watched those values change you know it is compensating and doing a fine job at it. Just like SDRC is trying to compensate.

I never owned a RSP1, RSP2, nor a RSP2 pro. RSP1a is my first and best over any rtl-sdr I ever owned. I believe it might be limits to the API in 3rd party software. Just remember one's favorite SDR software doesn't make it perfect nor without limits. I still like SDRuno alot too. I am being fair, rightfully.

[sunwave]

Hi,

My suggestion is that this is either background noise or more likely AGC, if AGC then you have some strong signals which are 'pumping' the AGC?

Probably Radio Marti at the hour of the video recording. Radio Marti is always strong here in Oklahoma City, Oklahoma USA in the 41m broadcast band in which Radio Marti is right next to the 40m band. I turned the AGC off then the pumping stopped. Other than that, your SDR-Console works just fine for the RSP1a.

[KA1GJU]

Sunwave,
"RSP1a is my first and best over any rtl-sdr I ever owned."

This month, Airspy traditionally has a Black Friday Sale on their SDR's, buy the Airspy HF+ discovery and you will be even more amazed.
The RTL's I use for an ADSB RXR for Flight Radar24, nothing else. The RSP1A I have, I try not to use it due to easily being overloaded from AM BC stations when used on good antennas. The Airspy hass less controls to fiddle with (only preamp on/off or visual gain), no extra drivers to load, and work well, providing you don't need to look at large swaths of spectrum at the same time (912kHz max on the HF+ Discovery). The RSP1A has all these adjustments, top image. While the Airspy (lower image) has fewer adjustments, which the first two you rarely touch. The pre-amp is turned on on 20m and higher, and the visual gain maybe once and a while.

Choices.jpg (25.14 KiB) Viewed 1446 times

Since Radio Marti is an AM SW BC station, you will not get what you are showing on the waterfall/bandscope. Your's goes from off to full on @00:26, then several steps of 2 seconds each reduced QRM @0036 before returning to off, then it increases back up in equal time of 00:02 steps to full on.
I'm betting on something nearby. Are you out in the country or in the city? Try to think of something near by that operates in steps of increasing/decreasing power of ~2 seconds long. For HF DFing of QRM, I use a 1m diameter active loop. The nulls are VERY sharp and deep. With just a few readings and plots on a paper map, I have found some interesting sources.


73 GL locating the source!
Kriss KA1GJU