[App_rpt-users] Noise Problem with URI and Voter Comment

hwstar at rodgers.sdcoxmail.com hwstar at rodgers.sdcoxmail.com
Tue May 4 13:46:22 EDT 2010

> From: MICHAEL SMITH <kb8wlw at me.com>
> Date: 2010/05/04 Tue AM 10:12:47 PDT
> To: app_rpt-users at qrvc.com
> Subject: [App_rpt-users] Noise Problem with URI and Voter Comment
> Sorry guys I just realized when I was hitting reply, I was replying directly to the individual.  I would guess proper etiquette would be to email the group.  Or at least CC the group.
> Thanks for all of the suggestions, I will try adding in a resistor or a voltage divider.  I will have to check to see if I have a 1:1 transformer laying around.  And yes the "RADIO TUNE TXVOICE" was on the far low side.  I will also double check to see if the monitor is creating the noise by turning it off.
> I thought the same thing (regarding local HT noise) and hooked up the audio input leads to the audio path and seen this (hopefully I can attach a picture).  I also had someone off site confirm they heard the noise.  I did not think about trying to figure out the frequency.

Looks like coherent noise from the 1ms interrupts Asterisk uses.  Probably sounds like a raspy 1kHz tone. Try the voltage divider first. Your scope picture shows 10mV of noise (assuming a x1 probe ad 2mV/div). I'd try a 20:1 voltage divider ratio. BTW: The 1:1 transformer will not help as the ground from the URI still needs to be connected to the radio for proper operation of the control signals COR and PTT and the isolation action of the 1:1 xfmr will be defeated.

Another approach would be to drive the TX modulator directly and not use the mic input.


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The asterisk computer is powered by a local AC outlet and the DC supply shares the same AC circuit.  The AC and DC grounds are bonded.  The DC supply also floats about 650 amp hours of battery back up.  

Even with all the batteries, I never had any luck using a inverter or a UPS tied to the DC buss.  I thought it would be nice to power the windows based echo link computer from a computer grade UPS (or inverter) that uses the main DC supply with the batteries.  But it introduces to much noise into the system that seems to only shows up on the UHF machines.  So I have to have battery back up for the PC's separate of the system.  Has anyone ever tried a "Car Computer" case that is designed to run off of 12 volts DC?  

I should have some time Wednesday night to try all of the suggestions, Thanks again.  I will keep everyone posted.


Mike / KB8WLW
145.410  MHz PL 110.9
224.480  MHz PL 141.3
442.225  MHz PL 131.8
442.450  MHz PL 131.8
927.6125 MHz PL 131.8
Echo Link Node # 146520
This is a KB8RST Sponsored System
kb8wlw at me.com 

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