[Shop-talk] Ground loop?

[Doug Braun]

Is the power supply's negative terminal isolated, or is it connected to the
power supply's chassis and line cord ground?
Does the radio have a real ground connection, or just the power supply
negative line?
If the radio chassis is "floating", and you connect it to a PC whose
chassis and USB, etc., connectors
are actually grounded via the line cord, strange things could happen.

Doug (NA1DB)



On Thu, Feb 13, 2014 at 11:10 PM, Dave Cavanaugh <cavanadd at frontier.com>wrote:

> I know we have a bunch of people that here that know a lot more about
> electronics than I do, so here is a ground loop question. Shop content:  I
> had the power supply stored out in the shop for two weeks.
>
> I have a new Yaesu FT-7900 dual band mobile ham radio I use for my base
> station.  I had intended to run it from a Pyramid 12 amp 12 VDC
> conventional power supply.  It (the power supply) is a big, heavy brick.
>  In limited use it seemed to work fine.  Then I tried to hook up a
> programming cable to upload my channel info into the radio via a USB
> programming cable from my desktop computer.  Every time I plugged the USB
> cable into the computer (the other end was plugged into the radio) the
> radio would shut down.  It shut down as soon as the USB male end touched
> the computer USB port.  This was the only connection between the radio and
> the computer.  Remember, the radio is being fed from a 120 VAC in, 12 VDC
> out power supply.  Both the computer and the power supply are plugged into
> the same wall outlet circuit.
>
> One of my radio forums suspected some kind of ground loop problem, and
> suggested I switch power supplies.  I just happened to have another power,
> an MEJ 25 amp "switching" power supply (a little, not so heavy box).  I
> didn't use this power supply initially because it has an annoying fan and
> the Pyramid doesn't have a fan.  Anyway, switching to a different power
> supply fixed the problem.
>
> What's going on, and what do I need to do to the other power supply to fix
> the ground loop issue.
>
> And can someone please explain what's going on with the "ground loop"
> business?  I went to ME school, not EE and I didn't have to learn about
> ground loops to get my Technician's ticket.
>
> Thanks
> Dave
> KG7HBQ
> _________________