adjust bandwidth for WFM

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haplessdiyer
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Joined: Wed Jul 10, 2019 1:15 am

adjust bandwidth for WFM

Post by haplessdiyer » Fri Jul 12, 2019 1:29 am

Mike maybe you can answer this one too.
Since I have the software basically working rather than add to my last thread like I did before I decided to post a new entry.
As I was listening to some FM broadcast stations I could hear distortion and I could tell that the problem was that the WFM wasn't quite wide enough. You can hear this on your U tube posting at about 5:20 into it. You can also see it on the scope as you see signal content outside the envelope of the filter that is used. It may depend somewhat on how strong the FM stations are modulating but many of them I hear are distorting . This is not a big deal, I was just wondering how that adjustment can be made. Maybe this not supposed to be end user adjustable?
Last edited by haplessdiyer on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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mikeladd
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Re: adjust bandwidth for WFM

Post by mikeladd » Mon Jul 15, 2019 7:32 pm

When I listen to FM broadcast stations 87.9–107.9
I use ZERO IF mode (MAIN panel) @ 5 Mhz of bandwidth with the RF GAIN at max.
I give myself separation between the TUNE and the LO
I set the RX control for FM/SWFM/192k.

If the station is weak but in Stereo. I use the FMS noise reduction from the EX CONTROL,

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mark.
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Joined: Tue Oct 03, 2017 9:14 pm

Re: adjust bandwidth for WFM

Post by mark. » Mon Jul 15, 2019 7:39 pm

I listened to slightly distorted FM broadcast band stations for many months until one day I discovered that I need to turn the SDRuno volume slider down farther than when listening to anything else. Cleared it right up. That was more than a year ago with an older version of SDRuno. I don't know if the problem still persists. I have the slider turned lower all the time now and boosted the slider on my sound card instead.

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mikeladd
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Re: adjust bandwidth for WFM

Post by mikeladd » Mon Jul 15, 2019 9:37 pm

I have found the default volume level in Uno to be good. If you crank it near max it will distort. I have my Windows output volume at 100%
I leave Uno's volume alone and adjust my speakers volume as needed.

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mark.
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Re: adjust bandwidth for WFM

Post by mark. » Wed Jul 17, 2019 4:17 am

In my case the volume slider was up maybe half way. Everything but FM stereo sounded fine. I could move the slider up further with no issues in any other mode. FM stereo requires less than half way up. Its not a matter of overloading the sound card input. My guess is its the software.

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Tech_Support
Posts: 497
Joined: Mon Jun 01, 2015 7:00 pm

Re: adjust bandwidth for WFM

Post by Tech_Support » Wed Jul 17, 2019 8:40 am

In all modes apart from SWFM, audio limiters prevent the audio level from overloading the audio DACs. In SWFM, these are disabled because of the need to decode the RDS and stereo signals (which appear in the demodulated audio path) and so of you have the volume slider set above 50%, you risk audio clipping on the audio DACs. It has been like this since the days when the software was Studio 1 and at some point, we will revisit this section of the code to see whether it can be improved. Note this ONLY occurs in SWFM mode and does not occur in WFM mode.

Sincerely

Tech_Support

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