loud spurs in audio output

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W1ABA
Posts: 10
Joined: Mon Jul 16, 2018 8:19 pm

loud spurs in audio output

Postby W1ABA » Wed Aug 15, 2018 5:11 am

Hi All,

I've been doing some great things with my relatively new RSP1A, using linux and cubicsdr program. Ever since the first time I got it running, I've been noticing high pitched audio whine in the speaker from my system whenever I use the RSP1A however. Today, I learned why the whine is so annoying using audacity to plot the output spectrum. Note that the whine IS NOT dependent on the frequency of operation of the RSP1A.

The whine is so annoying because it is about 5 different frequencies, not just one. And, the 2 largest spike in the audio output spectrum are many db above the average baseline!

I made 2 plots on 2 different aircraft band frequencies. I have attached the screen captures of the cubicsdr screen used to take the measurements and the spectral analysis of the output frequencies as displayed with the audacity 'analyze' command. And, I've attached 3 second .wav files for both the different receiver frequencies.

What the spectrum plots show is a nasty output spike at 999Hz and a second nasty output spike at 1904Hz. The spikes are 14.5 db above the noise floor at 999Hz and 13db above the noise floor at 1904Hz, the other spikes are higher in frequency, but range from 4 to 7db above the noise floor. Plots from both frequencies show the same frequencies and amplitudes.

I very often do plots of audio spectrum on my punchbox, the frequency spikes seen from the RSP1A are not due to any quirk in my computers sound system.

Does anyone know why these spikes are there or how to eliminate them?? They're annoying as heck::>

Regards,

Art

Please note, I tried to submit all five files, including the .wav files, so others could hear what I was hearing. The forum software will not allow submission of the other file types, so I could only upload the spectral analysis screen captures. I'll happily supply the other attachments by email-drop me a line if you'd like to have the other wav file and documents....ky1k attt myfair-point ddoott nett......delete the '-' in 'fair-point'.
Attachments
127.925MHz.png
127.925MHz.png (104.28 KiB) Viewed 520 times
127.35MHz.png
127.35MHz.png (99.41 KiB) Viewed 520 times

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glovisol
Posts: 118
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: loud spurs in audio output

Postby glovisol » Sat Aug 18, 2018 3:28 pm

Hi Art,

Perhaps it is interference from the PC you use getting into the RSP1A through the USB port. If this is the case, an extra long (2m) EMI suppressed USB cable, with double shielding and ferrite suppressors at both ends could save the day....

Cheers,

glovisol

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W1ABA
Posts: 10
Joined: Mon Jul 16, 2018 8:19 pm

Re: loud spurs in audio output

Postby W1ABA » Sat Aug 18, 2018 6:25 pm

I think that's not the issue. I have a 6 foot USB cable, which is supposed to be double shielded. It didn't have EMI suppressing ferrites, so I bought some snap on ferrite beads. They didn't make any difference.

The thing about the tones is that they don't change frequency when the frequency of the RSP1A is changed, so I suspected a baseband noise source built into the RSP1A, which might have been switching power supply noise picked up the digital converter. Or, it might be the digital converter picking up the PLL reference frequency. I'm going to do some more tests later to see just exactly how 'band' sensitive the noise is.

I did notice that the annoying whine type of noise is much less severe outside of the aircraft band.

ABA

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glovisol
Posts: 118
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: loud spurs in audio output

Postby glovisol » Sat Aug 18, 2018 8:29 pm

In the beginning, using an RSP2pro, I had whines and interference all over the place. This state of affairs drove me crazy for three days...until I went to the shop and purchased another (expensive) USB cable: then all the mystery problems just disappeared in one go.....why not try another cable? Seems quick & fussless to me!

glovisol

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W1ABA
Posts: 10
Joined: Mon Jul 16, 2018 8:19 pm

Re: loud spurs in audio output

Postby W1ABA » Sun Aug 19, 2018 12:08 am

I've been a ham radio operator for years, an avid homebrewer and have done my share of cleaning up other people's design(s) disaster-which most of the time means 'built without rf shielding' or using shielded cable that isn't!

When I buy a usb cable, especially for a communications project, I don't buy junk!

I do have a high quality usb cable for the RTL-SDR (which was bought recently for the RTL-SDR specifically), but the usb cable I have for the RSP1A is an unknown. I am deciding whether to buy another usb cable for the RSP1A or whether to cut the USB A connector off the existing cable and replace it with a B type cable so it can be used with the RSP1A. But, eventually, the cable will be a high grade unit, even if I have to build it myself::>

And, I have an update on the original problem-which was the whine/squeal issue.

I have tracked the problem down to CubicSDR software, but only when the software is set up to listen to multiple frequencies at the same time. All my profiles for the various bands I use monitor multiple frequencies at the same time!!! I think I made my first profile on day 3 (after I got the software installed). So, if I do not load a profile and just monitor a single frequency by setting it manually, there is no whine/squeal! I wish I had realized this before I posted here::>

I desperately need the ability to monitor multiple frequencies due to the nature of my work with the RSP1A, but unless I can get some serious issues with CubicSDR (my opinion) resolved, I will not be using it in the future.

TY for the reply to my post, it's much appreciated.

ABA

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vsonnier
Posts: 6
Joined: Wed Jun 13, 2018 4:44 am

Re: loud spurs in audio output

Postby vsonnier » Sun Aug 19, 2018 6:11 am

Please submit an issue to GitHub, trying to be as complete as you can:
- Linux version ?
- CubicSDR version, how was it compiled, ...etc.
- Audio ouput used (Jack, Pulse Audio, OSS, other ?)
- Submit the CubicSDR session file for your use case,
- Submit example WAV files,
- Screenshots, screenshots, screenshots of CubicSDR interface.

Unless you already have the "latest" GitHub master version, the answer is likely to be the same: use it preferebly.
Conviniently, this has just been labelled "0.25" in master.

Even more practical, SDRPlay has released an indeed very good step-by-step video on how to rebuild CubicSDR and dependencies from scratch
on Linux:
https://www.sdrplay.com/new-video-guide ... n-process/

Here: https://github.com/cjcliffe/CubicSDR/issues use the "New issue" button.

BTW, never "heard" anything like this, but it is indeed difficult to guess whitout examples.

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glovisol
Posts: 118
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: loud spurs in audio output

Postby glovisol » Sun Aug 19, 2018 7:34 am

Hi Art,

I apologise if I gave you the impression to offend or polemise, I was just trying to help by sharing my experience. Kind regards,

glovisol

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