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compgndloop [2007/05/20 20:44] (current)
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 +====== Computer Control & Ground Loops ======
 +**From the Ten-Tec Reflector May 2, 2007**
  
 +I got audio distortion whenever I operated the Omni VI+ with my amp, but only if the Omni was connected to my laptop.  I found a solution that might help someone else.
 +
 +I tried most everything.  The only real connections from the computer to the radio were the audio out to computer sound card cable and the CAT serial cable.  I solved the audio out problem with a Radio Shack audio isolator.
 +
 +Now, the only other connection between the radio and the computer was the DB25 cable. Mine was DB25 to DB9 to USB/Serial converter to computer.  I rebuilt the DB25 by removing everything but pins 2, 3, and 7 for TX, RX, and ground.  Didn't help.  I put ferrites on 
 +the wires (connector 72) that take the serial input to the logic board in the Omni VI. Didn't help.  I put .01uf caps from pins 2 and 3 to pin 7 (ground).  Didn't help.
 +
 +Then I got to thinking.  The solution to the audio cable had been an audio isolator, called a "Ground Loop Isolator" by Radio Shack.  Hmmm, ground loop.
 +
 +I cut the ground wire on the DB9, removing a ground connection between the computer and the radio.  I doubted the CAT interface would work with just pins 2 and 3 between the computer and the radio.  But, it did.  And, my audio distortion when using the amp was 
 +gone.  Not sure why it still works, but I'm not asking any questions.
 +
 +So, the problem is solved...
 +
 +Thanks to those who provided suggestions.
 +
 +73 de K1ESE\\ 
 +John
 +
 +----
 +**May 2, 2007**
 +
 +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