Noise during feed

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freema22

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Hi guys,
I have given up trying to use an SDR to feed my scanner. I have reverted to the "normal" method of using a scanner and a USB soundcard dongle. The problem I am struggling with now is noise when there is no traffic. There is a constant hum. I have tried installing ferrites and a ground loop isolator, but no change. The USB dongle is very basic, with just a mic input and headphone output. No line-in. There are no settings in alsamixer that I can adjust, such as turning off ACG. Does anyone have any ideas?

Walled Lake and Commerce Township Fire Dispatch Live Audio Feed is my feed to hear for yourself.

Thanks!
Mike
 

wcoriston

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If your feeding a mic level input it's likely the incoming signal is too hot for it. Where are you feeding a line out of the scanner? Speaker level is the hottest signal followed by line and then mic level.
 

freema22

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If your feeding a mic level input it's likely the incoming signal is too hot for it. Where are you feeding a line out of the scanner? Speaker level is the hottest signal followed by line and then mic level.
The scanner I am using only has a headphone jack. No discriminator or line-out. I have the volume set very low, but if the audio is too low, the hum overpowers the actual traffic.

Mike
 

kruser

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The scanner I am using only has a headphone jack. No discriminator or line-out. I have the volume set very low, but if the audio is too low, the hum overpowers the actual traffic.

Mike
What ground loop isolator did you try, have a link for it?
It does sound like you may still have a ground loop problem.

There are also some poor usb sound devices out there although I've used the ones that only cost a buck each before and they worked amazingly well.

If you are back to using the scanner for the audio, try running it on battery only and see if the hum goes away. As a second test, disconnect any external antenna you may be using on the scanner and see if power or antenna removal or both are needed to eliminate the hum.

Headphone jack audio is better than speaker level but not really by very much. I'm with wcoriston in that you may simply be feeding to hot of an audio signal into the usb sound device.
 

freema22

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What ground loop isolator did you try, have a link for it?
It does sound like you may still have a ground loop problem.

There are also some poor usb sound devices out there although I've used the ones that only cost a buck each before and they worked amazingly well.

If you are back to using the scanner for the audio, try running it on battery only and see if the hum goes away. As a second test, disconnect any external antenna you may be using on the scanner and see if power or antenna removal or both are needed to eliminate the hum.

Headphone jack audio is better than speaker level but not really by very much. I'm with wcoriston in that you may simply be feeding to hot of an audio signal into the usb sound device.
So, I did some experimenting, and I may have solved the issue. I REMOVED the Ground Loop Isolator and the buzz went away. Seems counter intuitive, but that is exactly what happened.

I did try running it on batteries only, and there was no change and I have tried both the stock rubber duck and an external antenna. The external antenna was much worse.

I will update if the noise returns or am able to locate the source of the noise to begin with.
 

ChrisABQ

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You have a lot of noise on your feed, are you actively using the computer while providing the feed? It sounds like other processes are running in the background.
 

freema22

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You have a lot of noise on your feed, are you actively using the computer while providing the feed? It sounds like other processes are running in the background.
The feed is literally the only thing running on this Raspberry Pi.
 

DC31

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That sounds like noise originating from your scanner. Unplug the audio cable from your scanner and plug it into the earphone jack on your IPhone (or other). Then play some music from pandora or whatever on the phone and see how that sounds over BCFy. If that sounds good, it pretty much rules out a hardware problem on the pi.

If you have the scanner output connected to a mic input on the sound card, you want the scanner volume control about as low as it will go.
 

freema22

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That sounds like noise originating from your scanner. Unplug the audio cable from your scanner and plug it into the earphone jack on your IPhone (or other). Then play some music from pandora or whatever on the phone and see how that sounds over BCFy. If that sounds good, it pretty much rules out a hardware problem on the pi.

If you have the scanner output connected to a mic input on the sound card, you want the scanner volume control about as low as it will go.
Testing done this morning:

1) Scanner unplugged from Pi: Noise persists
2) Everything but power supply unplugged from Pi: Noise persists
3) USB hub unplugged: Noise persists
4) Replace WiFi dongle with ethernet connection on Pi: Very slight improvement
5) I didn't try the phone connection, but I figured since the noise was persisting with the radio unplugged, it wouldn't make a difference.
6) Confirmed that the noise was worse when using the ground loop isolator.

Things are pointing to the power supply as the source. This is an "official" Raspberry supply. Not sure if that makes it better or worse.
 

DC31

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Yes, points toward power supply or some other nearby RF source. It could even be another power supply to another piece of equipment in the area.
 

freema22

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I have solved the problem! Turns out the USB soundcard that I was using was generating the noise. I bought a new one and it is night and day! The background noise is completely gone and the audio quality is fantastic. Thanks for all of the input!
 

Danny37

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I have solved the problem! Turns out the USB soundcard that I was using was generating the noise. I bought a new one and it is night and day! The background noise is completely gone and the audio quality is fantastic. Thanks for all of the input!
Can you please link the usb sound card you purchased. I'm having the same issue.
 

W1cjf-1

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