[arm-allstar] Noise on the output rpi2 and uri.

[Jim Korenz]

If it's RF getting into the audio, try a 1000pf cap from hot to ground. The audio is AC coupled into the URI, if you use those inputs. If you still have noise, try a 10uf cap in series with the shields, i.e. isolate the radio ground from the URI ground, or use an audio transformer.
   JimK  N8PXW

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On Sun, 5/24/15, Doug Crompton <doug at crompton.com> wrote:

 Subject: Re: [arm-allstar] Noise on the output rpi2 and uri.
 To: "ARM Allstar" <arm-allstar at hamvoip.org>
 Date: Sunday, May 24, 2015, 10:32 AM
 
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 #yiv7486914851 Andrew,
 
    You didn't describe
 what the noise sounds like but most noise comes from some
 switching source. It could be a cooling fan, a switching
 power supply, etc.  Also have you eliminated RF problems?
 Since this is on TX only maybe put the transmitter on a
 dummy load just to check. Are you using shielded cable for
 the radio connection? Are the grounds all good?
 
 You need to probe at different
 points along the path to see where the noise is being
 introduced. Asterisk Allstar itself would not introduce any
 noise, at least not objectional noise as you describe.  
 
 What are you using for a power
 supply for the 5 volts? 
 
 73 Doug
 WA3DSP
 http://www.crompton.com/hamradio
 
 
 Date: Sun, 24 May 2015
 23:41:41 +1000
 From:
 andrew.gilbett at gmail.com
 To:
 arm-allstar at hamvoip.org
 Subject:
 [arm-allstar] Noise on the output rpi2 and uri.
 
 Hi All,
 I have just setup a RPi2 & URI combo and it
 work quite well. Except it has quite a high noise level on
 the tx.
 I noticed that this was also the case on the
 beagleboard xm and lox board combo as well. I was hoping it
 was peculiar to that hardware but it is not
 unfortunatly.
 Basically it sounds like it is being encoded
 with gsm  and being compressed with noise added to it.
 If I connect via IAXRPT the signal is quite
 clear but not perfect so there is a little bit of noise on
 the input but it is the output where it is degraded
 again.
 I am using Simoco SRM9005 radios using the rear
 io on the db15.
 Could someone shed a little light on the audio
 path through asterisk and where noise could be coming from
 there?
 This is for an ultra portable repeater that is
 carried up hills for events and I have found that apt_rpt
 and asterisk is awesome because it is a complete voip
 switch. Keep up the good work.
 Andrew
 
 VK2XAG
 
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