[arm-allstar] High pitch hum on audio

[jgnatow]

The pi is a 3 not sure of revision (b or b+). I will definitely try
turning off bluetooth!

Thanks!



John "Jason" Gnatowsky

KG4FJC

434-841-9290

On Feb 7, 2022 at 12:50 PM, Derek Chauran via ARM-allstar
<arm-allstar at hamvoip.org> wrote:


Good luck, I have had this problem on a number of PIs and have tried
everything you mentioned. What kind of PI? Have you tried disabling
bluetooth (add dtoverlay=disable-bt to /boot/config.txt)? That seemed
to help with one of my nodes. I also used a really long USB extension
cable to the CM108 on one of my nodes, and wrapped it through a mix 31
ferrite about a dozen times which may have helped, though so did
repositioning cables on that node.


________________________________


From: ARM-allstar <arm-allstar-bounces at hamvoip.org> on behalf of "john
gnatowsky via ARM-allstar" <arm-allstar at hamvoip.org>


Sent: Sunday, February 6, 2022 5:44 PM


To: ARM Allstar <arm-allstar at hamvoip.org>


Cc: john gnatowsky <jgnatow at yahoo.com>


Subject: [arm-allstar] High pitch hum on audio










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












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