[arm-allstar] Portable node grounding issue

[Lonny Barry]

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