8 Raspberry Pi Rack with static

vinny2010b

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I made a raspberry pi icecast server with 8 pies powered by POE and 8 scanners. Anyone need the image Ill post it. It look really nice and works great. But I get allot more static then I would like. Especially on the NYC Manhattan frequency, scanners are also located in NYC Manhattan. I used a stock antenna with a 8 Port MCA208M. Any suggestions on reducing static? BTW I like looking at everyone's setup really nice work.
 

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737mech

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Static all the time or when someone is talking? Is it only on certain frequencies? You could get Ferrite chokes and put them on the power cables to the scanners. You could wrap that pie rack with copper tape. Check the coax for shorting to shield. No audio cables correct? If yes then install ground loop isolators.
 

RFI-EMI-GUY

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1) Is the cabinet for the PI's made of metal or plastic?
2) You should be aware that if you are picking off RX audio from the speaker jacks, you need an audio isolation transformer to present a balanced load to the radio's BTL (Bridge tied load) audio amplifier. Otherwise you may damage the radio and/or introduce noise and distortion. These are called ground loop isolators, but dont go cheap on these, you need actual transformers, not some sketchy Chinese widget with capacitors. Radio Shack used to sell good ones and they were stereo having two transformer's so you could use to isolate two receiver and sound cards.
 

KE5MC

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Before I would attempt any 'fixes' with a multi-channel setup like yours I would switch equipment around and/or enable one at a time. Seeing if the static moves around or is enable by a specific channel.

Nice setup!
 

Pete27a

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Great setup!!!!!!!! Where are you broadcasting them to???
 

vinny2010b

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Static all the time or when someone is talking? Is it only on certain frequencies? You could get Ferrite chokes and put them on the power cables to the scanners. You could wrap that pie rack with copper tape. Check the coax for shorting to shield. No audio cables correct? If yes then install ground loop isolators.
Hello. Thanks for the reply... Static only when talking. Its all on the scanners all the frequencies. I will install ferrite chokes and ground loop isolators thats easy. Wrap the rack in copper tape? Like a mummy? not sure
 

vinny2010b

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1) Is the cabinet for the PI's made of metal or plastic?
2) You should be aware that if you are picking off RX audio from the speaker jacks, you need an audio isolation transformer to present a balanced load to the radio's BTL (Bridge tied load) audio amplifier. Otherwise you may damage the radio and/or introduce noise and distortion. These are called ground loop isolators, but dont go cheap on these, you need actual transformers, not some sketchy Chinese widget with capacitors. Radio Shack used to sell good ones and they were stereo having two transformer's so you could use to isolate two receiver and sound cards.
The cabinet is all plastic. Can u suggest a a ground loop isolator?
 

vinny2010b

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Before I would attempt any 'fixes' with a multi-channel setup like yours I would switch equipment around and/or enable one at a time. Seeing if the static moves around or is enable by a specific channel.

Nice setup!
Do u think there too close?
 

KE5MC

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...snip...
Wrap the rack in copper tape? Like a mummy? not sure
1st pass... try aluminum foil. If it doesn't work save for next years Thanksgiving or maybe the Christmas ham. :)

On a serious note, not likely to eliminate static and I suspect internally generated. On the other hand you never know with interference what the solution turns out to be,
 
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KE5MC

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Do u think there too close?
I missed that question.
Not likely proximity is an issue. I saw the comment where static only when talking. Makes me think analog audio is maxing out an ADC somewhere in the setup. Maybe a review of audio level for each channel making sure if diagnostic tools are available that nothing is overdriven. Or maybe something on the Pi is running in background messing with the audio stream. Another thought is POE across that many device is not a good approach.
Good Luck, hope you get it sorted out!
Mike
 

RFI-EMI-GUY

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The cabinet is all plastic. Can u suggest a a ground loop isolator?
I used to recommend ones from Radio Shack but they are no longer available unless you go to Amazon and they are twice the normal price. Amazon has a bunch of Chinese ones that are small and either have no transformer and use capacitors which provide no DC load to tha BTL amp. , or have tiny transformers that might get saturated from the BTL amp in the scanner. I would be wary of some that have phono jacks mounted inside a metal can because if the plug touches the can, the DC isolation is lost. Pigtails are better.

They have transformers inside so the ground loop isolator can pick up noise from nearby AC magnetic fields so you might get hum and crosstalk with cheap un-sheilded transformers. There are some inside metal boxes and cans that have pigtails, so those would be my first choice.

This one might be a good choice:



Some teardowns of others.

https://www.youtube.com/watch?v=4t1H5TjQoyQ
 
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