Page 1 of 2

distorted FM

Posted: Wed Nov 13, 2019 6:25 pm
by aurgathor
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#

Re: distorted FM

Posted: Wed Nov 13, 2019 6:31 pm
by nospam
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?

Re: distorted FM

Posted: Wed Nov 13, 2019 6:46 pm
by aurgathor
> 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.

Re: distorted FM

Posted: Wed Nov 13, 2019 7:16 pm
by aurgathor
> 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 3252 times

Re: distorted FM

Posted: Thu Nov 14, 2019 9:13 am
by Username
Deactivate Filter Audio and look if some other Audio, Noise Filter also Deactivated.

Re: distorted FM

Posted: Fri Nov 15, 2019 12:23 am
by nospam
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.

Re: distorted FM

Posted: Fri Nov 15, 2019 7:33 am
by aurgathor
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 3120 times

Re: distorted FM

Posted: Fri Nov 15, 2019 1:04 pm
by radiolistener
I recommend to use HDSDR. Because SDRuno and SDR# is too buggy.

Re: distorted FM

Posted: Sat Nov 16, 2019 2:41 am
by dlritter
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?

Re: distorted FM

Posted: Sat Nov 16, 2019 7:03 am
by aurgathor
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.