[arm-allstar] Portable node grounding issue

[Doug Crompton]

Lonny,

 The FOB gets its ground via the USB connection. Then there should be a
ground between it and the radio. For the DMK-URI FOB that would be pins 19
and 20 of the DB25. You did not mention what FOB you are using or how your
power was connected? Are you using the same supply for the radio and Pi. Of
course in that case the Pi would be fed through a 12V to 5V converter.
Also you say voltage test and putting your hand on it. Not sure what you
are using to test voltage. Do you have a voltmeter that would measure the
voltage between the points you are suspecting have a voltage differential?


*73 Doug*

*WA3DSP*

*http://www.crompton.com/hamradio <http://www.crompton.com/hamradio>*



On Sun, Nov 4, 2018 at 10:20 AM "Lonny Barry via ARM-allstar" <
arm-allstar at hamvoip.org> wrote:

> Good Sunday morning,
>
> I'm looking for a little insight into portable node grounding.
>
> I am assembling a portable node in a pelican case.
> Pi 3b+, RepeaterBuilder FOB, SMAKN 5v step down, Power Down Controller with
> 9v battery, Modified 888s.
>
> At the moment, I'm reading current at the female end of the FOB (without
> the radio connected).  If I grasp the DB9 connector on the FOB, the voltage
> tester silences.
>
> It seems to me that there is a grounding issue somewhere. I've already
> exchanged the USB cable to the FOB to no avail.
>
> How is anyone else getting a ground for a portable node, especially one
> contained in a plastic box?
>
> As an aside, the symptom that lead me to this issue is occasionally the
> node / radio will leave the PTT stuck open. By touching the USB housing on
> the Pi or the DB9 connector on the FOB, the PTT closes.
>
> Thank you for your suggestions. I'm admittedly not an electronics whiz, but
> I did get into this to learn.
>
> Lonny
> KG5IGJ
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