[Shop-talk] Ground loop?

[Mark Endicott]

Dave,  You also need to consider the ground on your antenna system.  
Your older design analog power supply probably shares the earth ground 
with your house.  If you have a ground on the antenna or an antenna that 
is shunt fed (most gain antennas) you will have a loop back to earth 
through the antenna system to the radio chassis.  Try to unplug the 
antenna and see if your problem is resolved.  If it is measure for 
voltage between the antenna cable shield and the chassis of your radio 
both with and without the usb connected, it should be zero.  If the 
radio turns off when you connect the USB cable it is probably the power 
supply shutting down due to it's current limiting. Generally all grounds 
need to be tied together at one point.  Your switching supply most 
likely has a floating ground, neither output is connected to earth.   It 
can be a PIA to sort out grounds but if they are common to one point 
there shouldn't be a loop.

Mark
Nashville

On 2/14/2014 9:05 AM, w wrote:
> On 2/13/2014 11:10 PM, Dave Cavanaugh wrote:
>> 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