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

[John Huffman]

I had a problem, described below.  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


John Huffman wrote:
> I have a problem when I operate my Omni IV+ (option 3).  The audio on 75 
> meter SSB and 10 meter SSB is distorted.
> 
> This only happens when I run the amp (Ameritron ALS-600).
> 
> This only happens if I connect cables between the Omni IV+ and my 
> laptop.  If I connect audio out on the Omni to the mic connection on the 
> computer sound card, I get distortion.  If I connect the RS232 output on 
> the Omni to the computer, I get distortion.
> 
> I have a decent ground.  But, I do not ground the computer and am not 
> sure where I would get into it to make a ground connection.
> 
> I have no problems using my K2/100 with the amp and the same computer.
> 
> I have loaded the lines between the Omni and the computer with ferrites 
> (cores with 10-15 turns and clip-ons on the ends of the connectors).  
> They didn't help.
> 
> So,
> Distortion with the OMNI VI+ and the amp if the computer is connected.
> No distortion with the Omni VI+ and the amp if the computer is NOT 
> connected.
> No distortion with the K2/100 and the amp with the computer connected.
> 
> Any ideas??
> 
> 73 de K1ESE
> John
>