[arm-allstar] ARM-allstar Digest, Vol 71, Issue 59

[cqdogxray at gmail.com]

Hum is often caused by some AC current flowing through the 0 vdc side of
whatever audio fob you are using. Voltage drop in the zero-volt wiring of
the USB/fob connection is effectively in series with both the transmit and
receive audio path.  A wall wart almost always puts some 60/120 Hz AC on the
DC minus lead (relative to ground elsewhere on your system) and the USB fob
offers no isolation for this.

If you can figure out how to do it, the cheap answer is to connect a
short/heavy wire from the DC minus lead of your RPI 5 volt supply to the DC
minus side of your radio's power supply.  These are the two sources of the
unwanted AC.  Second-best is to connect a short/heavy wire from some 0 volt
on the RPI to the chassis of your radio.  That is the critical part of the
circuit.

Using a 12/5 volt DC/DC converter to power the RPI also helps (using the
same 12 volts as supplying your radio).

Ken




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Message: 1
Date: Sun, 26 Apr 2020 04:04:45 -0400
From: Jed Barton <jed at jedbarton.com>
To: arm-allstar at hamvoip.org
Subject: [arm-allstar] hum on my allstar nodes
Message-ID:
	<CAOYEAerhpLL_neibghwjjS81bU_xt_cMo2cmWG_HR1rsO6R7cw at mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"

Hey guys,

So i'm sure i'm not the only 1 with this problem. I've got all my allstar
pies plugged in.  They each have their own power supply. It's the typical
wall wart.  They all produce a nice little hum that's just annoying.
I'm sure a lot of you guys have delt with this.  You hear it on the node
transmitter such as the Shari.  Any ideas for getting rid of it, or reducing
it?

Cheers,

Jed