[TenTec] RFI, Computer, Omni IV+ - SOLVED

[Stuart Rohre]

Indeed, John, you have a sneak ground loop path that was duplicated by pin 7 
ground.  You eliminated that 7 ground wire, and you now have only one 
ground, likely the chassis ground.  In some equipment, 7 was isolated from 
chassis which was pin 1 in original 25 pin RS 232 implementation.  Later, 
computer makers got lazy and often tied 7 and 1 together and used 7 only 
between devices.  Wonder if you had tried ferrites on 7 wire before you cut 
it?

You do ground the computer, but just do not know it.  Its ground is chassis, 
which goes to AC connector third pin.  (The green or green yellow wire).

RF has a way of getting into AC grounds and causing havoc.

Document what you did in case you disconnect things to take them to Field 
Day or portable some time.  You may need a way to replicate the pin 7 wire 
ground someday.  I keep stuff like that in the instruction manual for the 
rig or computer device, or on back of logsheet pages.  (I keep all logs 
forever).

73,
Stuart
K5KVH