[TowerTalk] logic ground & audio ground

[Jim Jarvis]

There were a couple of posts on this topic, so I won't
direct this at anyone in particular.

1)  You will not see logic ground in your radio.  It exists
internally, and is carefully controlled to keep EMI down,
and prevent RF from getting into the processors.  
    The interface is usually opto-isolated, and is floating
with respect to chassis.

2)  If audio shield were tied to chassis ground, and therefore
also to AC mains safety ground, you would stand a very good chance 
of having major ground loops.  
    Typically, the shield exists both to provide a return path for
current from the microphone element, and to shield the mic preamp
input from anything that might be riding on the ptt or 8v power
lines going out to the mic, within the microphone cord.  

N2EA
jimjarvis at ieee.org