[arm-allstar] High pitch hum on audio

[David McGough]

Hi John,

When you say the whine is on the "LINK ONLY," what do you mean??  Is the 
whine on the TX/RX from the CDM750, using an RA35?

What does the whine sound like? Do you have a recording?


73, David KB4FXC





On Sun, 6 Feb 2022, "john gnatowsky via ARM-allstar" wrote:

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> Hey all...need some hive mind input.
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> The layout...
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> Pi 3b+, 2 X ra-35, one cm108 modded.
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> 220 repeater (on ra 35) built with pair of tait tm-8100's.
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> Uhf half duplex link. Moto cdm750 (on ra35)
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> Gmrs repeater (on modded cm108) built with pair of moto cdm750's.
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> The problem...
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> There is a high pitch hum on both tx and rx audio on the LINK ONLY. Both repeaters are perfect audio.
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> What I've tried....
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> Grounding! I've run extra grounding to radio, pi, interface. No change at all.
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> Usb ports. I've changed usb ports/towers with the link interface.
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> Changed radios, cables (usb and harness).
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> Rerouted all cables and power wires.
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> Swapped ra35's.
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> Changed power supply to pi.
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> 
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> 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?
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> John "Jason" Gnatowsky
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> KG4FJC
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> 434-841-9290
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