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

[Patrick Perdue]

That is exactly why I had G7RPG add an SMA connector to my Microhub 
rather than using the internal antenna, so I could get the antenna away 
from the Pi and the rest of the components.

On 4/26/2020 4:54 PM, "Chris Smart via ARM-allstar" wrote:
> 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
>>
>>
>> _______________________________________________
>>
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>>
>> Visit the BBB and RPi2/3/4 web page - http://hamvoip.org
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