[Shop-talk] Ground loop?

[Dave Cavanaugh]

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