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

[Chris Smart]

Thanks Ken. Very interesting. I'll pass this on to the guy who built my 
node.



On 4/26/2020 12:57 PM, "Ken via ARM-allstar" wrote:
> 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
>
>
>
>
> ----------------------------------------------------------------------
>
> 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
>
>
> _______________________________________________
>
> ARM-allstar mailing list
> ARM-allstar at hamvoip.org
> http://lists.hamvoip.org/cgi-bin/mailman/listinfo/arm-allstar
>
> Visit the BBB and RPi2/3/4 web page - http://hamvoip.org