[arm-allstar] High pitch hum on audio

[jgnatow]

I'm leaning towards the pi being the issue. I have a pi4 i could put in for
testing.


John "Jason" Gnatowsky
KG4FJC
434-841-9290
On Feb 7, 2022 at 1:02 PM, Randy K7RHT via ARM-allstar <
arm-allstar at hamvoip.org> wrote:

I have had the same issues and finally switched from a Pi to a mini dell to
run the link for a test, besides the software issues created, the noise
went away so now to find the problem in the Pi.

Randy Thomas - K7RHT
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On Mon, Feb 7, 2022 at 9:50 AM, 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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