[arm-allstar] Portable node grounding issue

[Lonny Barry]

Hi Doug!
Thank you for the reply.

FOB : RepeaterBuilder's RIM-Lite (DB9)

Power : Wall wart to Anderson Power Poles INPUT : 120V - 60Hz / OUTPUT :
12V  1A
                =>  SMAKN 12v StepDown to 5v
                =>  Pi pins 4 and 6

Meters : Klien NCVT-1 voltage tester (rough identification)
              Commercial Electric MS8301A Multimeter for measurements
Radio is battery powered as I have yet to incorporate a battery eliminator

The DB9 is grounded at pin 9 which is also jumpered to pin 8 effectively
grounding it as well.

Intermittently im measuring .5 mV between the USB housing and the end of
the DB9 on the FOB, again, without the radio connected to the fob,

On Sun, Nov 4, 2018 at 9:27 AM "Doug Crompton via ARM-allstar" <
arm-allstar at hamvoip.org> wrote:

> 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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> >
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> >
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