distorted FM

Main forum to discuss RTL-SDR related topics.
aurgathor
Posts: 84
Joined: Wed Apr 25, 2018 8:14 am

distorted FM

Post by aurgathor » Wed Nov 13, 2019 6:25 pm

Currently, I'm using an RTL-SDR v3 and SDR# to listen to FM radio; however, I have occasional issues with distorted sound and I'm not sure if that's due to low signal level or something else. I tried various settings in SDR# to no avail. The dongle and the antenna are located outside. SDR# uses around 15% CPU. When I play music from a file (winamp, VLC) there is no audible distortion. Any idea on what could be causing it?

Attached is a screen shot of SDR#
Attachments
rtl-sdr-distort.png
rtl-sdr-distort.png (750.66 KiB) Viewed 556 times

nospam
Posts: 17
Joined: Tue Jan 03, 2017 10:08 pm

Re: distorted FM

Post by nospam » Wed Nov 13, 2019 6:31 pm

Have you tried adjusting the bandwidth of the filter? It looks like there is some clipping of content between the main signal and those 2 digital sidebands?

Have you observed the same problem on other FM stations?

aurgathor
Posts: 84
Joined: Wed Apr 25, 2018 8:14 am

Re: distorted FM

Post by aurgathor » Wed Nov 13, 2019 6:46 pm

> Have you tried adjusting the bandwidth of the filter?

Yes. Makes no obvious difference.

> It looks like there is some clipping of content between the main signal and those 2 digital sidebands?

Umm, err, I don't think that should be the case, but what can I possibly do with that?

> Have you observed the same problem on other FM stations?

Yes. And FM stations with lower signal levels are worse. I haven't specifically looked for stations without the HD sidebands, but I could try to look around to see if they sound any different.

aurgathor
Posts: 84
Joined: Wed Apr 25, 2018 8:14 am

Re: distorted FM

Post by aurgathor » Wed Nov 13, 2019 7:16 pm

> It looks like there is some clipping of content between the main signal and those 2 digital sidebands?

I just tried the below station, and it's not better than the other one.   It might even be slightly worse.

distort2.png
distort2.png (572.34 KiB) Viewed 542 times

Username
Posts: 505
Joined: Sun Oct 09, 2016 7:27 am

Re: distorted FM

Post by Username » Thu Nov 14, 2019 9:13 am

Deactivate Filter Audio and look if some other Audio, Noise Filter also Deactivated.

nospam
Posts: 17
Joined: Tue Jan 03, 2017 10:08 pm

Re: distorted FM

Post by nospam » Fri Nov 15, 2019 12:23 am

by click dragging the edge of the envelope so the bandwidth is expanded. My experience is that with most FM the distortion is due to using too narrow a filter, the FM modulation goes outside the filter. Another option, try installing sdruno. Its free too.

aurgathor
Posts: 84
Joined: Wed Apr 25, 2018 8:14 am

Re: distorted FM

Post by aurgathor » Fri Nov 15, 2019 7:33 am

I have deactivated "Filter Audio" and it didn't fix the issue.

I'm still playing with "Bandwidth" and no result on that yet, although I'm leaning toward "no effect".

I just installed SDRUno (latest version), and when I try to start it, it just exits with the below error:

no-rsp.png
no-rsp.png (25.19 KiB) Viewed 410 times

radiolistener
Posts: 58
Joined: Thu Jan 25, 2018 10:48 pm

Re: distorted FM

Post by radiolistener » Fri Nov 15, 2019 1:04 pm

I recommend to use HDSDR. Because SDRuno and SDR# is too buggy.

dlritter
Posts: 42
Joined: Mon Nov 23, 2015 1:08 am

Re: distorted FM

Post by dlritter » Sat Nov 16, 2019 2:41 am

the last version of SDRuno to support EXTIO devices such as the RTL-SDR was 1.22. Remember only SDRuno.EXTIO.exe supports the RTL.. Much like SDR# does not support the RSP.

Do get any clear audio from anything?

aurgathor
Posts: 84
Joined: Wed Apr 25, 2018 8:14 am

Re: distorted FM

Post by aurgathor » Sat Nov 16, 2019 7:03 am

It used to be OK most of the time with occasional distorted sections, then for testing I brought both the dongle and antenna inside, and it was almost unlistenable when they were inside. Took them outside again, but it's still below what I consider acceptable, so listening to FM stations is off until I can reposition my antenna.

Because I have metal siding and a metal roof (also over my porch and carport where my antenna is) , now I think the root cause could be signal reflections. I plan to buy an outdoor antenna and mount it on my roof, at least 8 - 10 ft above it.

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