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compgndloop [2007/05/21 00:44] |
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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 |