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

[Stephen Rodgers]

Jim Duuuude wrote:
> All I know is that my cheap poopy monitor is NOTORIOUS for causing noise on transmit
> using a URI and a relatively high input impedance audio input to the transmitter.
> Sometimes, this can be corrected by putting a 1k resistor across the drive to the transmitter
> (the URI can easily handle that low of an impedance)
> 
> From: kb8wlw at me.com
> Subject: Re: [App_rpt-users] Noise Problem with URI and Voter Comment
> Date: Tue, 4 May 2010 10:01:37 -0400
> To: telesistant at hotmail.com
> 
> 
> 
> I thought I tried that, but will try again later today.  I have used two different monitors, CRT and LCD.
> 
> Mike / KB8WLW
> kb8wlw at me.com 
> On May 4, 2010, at 9:00 AM, Jim Duuuude wrote:turn off the monitor.. does the noise go away??
> 
>> From: kb8wlw at me.com
>> Date: Tue, 4 May 2010 08:41:06 -0400
>> To: app_rpt-users at qrvc.com
>> Subject: [App_rpt-users] Noise Problem with URI and Voter Comment
>>
>> I would love to see the ability to vote sites with the app_rpt software. After some side discussion with a fellow lister, I understand this would be very difficult to implement. Is there another alternative to time based GPS interface? I know it would not be "true" voting, but may be helpful in some cases. Would it be possible send time data to get the signals close and then select the receiver based on receiver signal strength?
>>
>> Now for my real question. I have looked through the archives and did not see anything, but I am suffering a noise problem. Ok I know what your thinking, it must be a ground loop. But I do not believe it is and I tried grounding everything. Let me give some history. I first setup Asterisk on a laptop and connected to a 900 MHz GE net station (again, thanks Doug for the help putting it on the air). Because the oscillator is always hot, you can here a carrier locally with an HT. Immediately I heard a high frequency whine that changed with screen changes on the computer. I tried three different computers and two other repeaters, a 440 Mastr II Station and home brew UHF Hamtronics. All of the configurations had the same noise. I even tried isolating some equipment offsite. During some trouble shooting, I noticed something that I thought was strange. I had the transmitter locked on the air by grounding the PPT line and when I stopped Asterisk by sending a "astdn.sh", th
>> e noise stops.
>>
>> The noise is only present when asterisk is running. The only thing in common is me and the URI. Any suggestions?
>>
>> Thanks,
>> 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
>> www.kb8wlw.com 
>> kb8wlw at me.com 
>>
>>
>>
>>
>> _______________________________________________
>> App_rpt-users mailing list
>> App_rpt-users at qrvc.com
>> http://qrvc.com/mailman/listinfo/app_rpt-users
> 
>  		 	   		  
> 
> 
> ------------------------------------------------------------------------
> 
> _______________________________________________
> App_rpt-users mailing list
> App_rpt-users at qrvc.com
> http://qrvc.com/mailman/listinfo/app_rpt-users

One question would be how the transmitter is being driven. If the sensitive TX microphone input is used, try a voltage
divider on the mic input so you can drive it harder from the URI. If you've go the URI output cranked down really low
because the mic input is sensitive, then any low level noise on transmit audio connection can be heard.

If the voltage divider trick does not work, another question would be how are you powering the radio and the computer?
Are the radio and the computer powered from DC and from the same DC source? If so, that is most likely a problem.

Grounding everything does not get rid of ground loops, in face it can make them worse! Audio noise can be caused by
current flowing through the ground shield of the transmit audio connection which will happen when the computer and radio
share the same DC power source. The best cure in this case is isolation of the computer power supply from the radio DC
power source.

Steve
WA6ZFT