[arm-allstar] High pitch hum on audio

[john gnatowsky]

>   Ok.... I have to come clean. I found the source of my noise. The source is NOT local. I have another machine setup at another hams house that i often use as a test machine/back channel.
 
>   It turns out the noise is coming from that link radio on tx and rx. When i checked the tx of mine, i was listening direct BUT on some kenwood radios, if you don't have tone enabled, you will hear the pl tone. Turns out the the other machine link rig is generating the noise both ways due to a noisy switcher PS.  
 
>   I want to thank everyone for their input and i want to apologize for not catching something so basic!
 
>  
 
>  
 
>   John "Jason" Gnatowsky
 
>   KG4FJC
 
>   434-841-9290
 
>   On Feb 6, 2022 at 8:44 PM, john gnatowsky  <jgnatow at yahoo.com>  wrote:
 
>  
 
>   Hey all...need some hive mind input.
 
>   The layout...
 
>   Pi 3b+, 2 X ra-35, one cm108 modded.
 
>   220 repeater (on ra 35) built with pair of tait tm-8100's.
 
>   Uhf half duplex link. Moto cdm750 (on ra35)
 
>   Gmrs repeater (on modded cm108) built with pair of moto cdm750's.
 
>   The problem...
 
>   There is a high pitch hum on both tx and rx audio on the LINK ONLY. Both repeaters are perfect audio.
 
>   What I've tried....
 
>   Grounding! I've run extra grounding to radio, pi, interface. No change at all.
 
>   Usb ports. I've changed usb ports/towers with the link interface.
 
>   Changed radios, cables (usb and harness).
 
>   Rerouted all cables and power wires.
 
>   Swapped ra35's.
 
>   Changed power supply to pi.
 
>  
 
>   None of this has had any affect at all! While testing i noticed that manual key of link radio (grounded ptt wire at ra35 connector without interface connected) and the tx audio is clean. I've injected signal in from service monitor without audio and noise is there. The only thing i can think of is the pi itself? Anything else i can try?
 
>  
 
>  
 
>   John "Jason" Gnatowsky
 
>   KG4FJC
 
>   434-841-9290
 
>  
 
>  
 
>  
 
>