Differences

This shows you the differences between two versions of the page.

@@ Line 1: / Line 1: @@
+====== 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.
+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).
+,\\
+Stuart\\
+K5KVH

Trace:

Differences

Navigation

Search

Toolbox

QR Code