[Lowfer] Computer noise - Ground Loops

Rye Gewalt [email protected]
Mon, 14 Jan 2002 18:42:14 -0500


I agree with Bill.  If you don't have audio and LF
isolation transformers to play with you'll never get to
the bottom of noise problems.  Ground loops are nasty
beasties.  You can use little radio shack audio
transformers for audio and wind a nice I:1 wideband
transformer on a toroid core with a little effort.  I
have been blessed with a North Hills 0017CC 50 ohm
isolation transformer that is good from 10 Hz to 5 MHz
-- I believe that these are common in the TV business
to break studio ground loops.

If you do discover any ground loops in your shack, be
careful not to trip over them as they are very
difficult to see....

Regards
Rye K9LCJ
Springfield, VA

"Ashlock,William" wrote:
> 
> Hi Bob,
> 
> Forget the magic. First you have to determine how the computer noise is
> getting into the signal path and make changes accordingly.
> 
> 1) Is the noise being picked up by your antenna? If so, the antenna has to
> be moved farther away from the computer.
> 
> 2) Is the noise getting into the antenna feed line? Short out the antenna
> (at the antenna itself)  to the coax lead-in with a 0.1uf capacitor and see
> if the noise remains. If it does you may need to add a 1-1 isolation
> transformer to the coax lead-in at the receiver to isolate the coax shield
> from the computer's chassis.
> 
> 3) Is the noise the result of a ground loop between the receiver and the
> sound card? May need an audio 1-1 isolation transformer there.
> 
> Sometimes the noise is persistent but 99 times out of a hundred there's a
> fix.
> 
> Good luck!
> 
> Bill WA
> 
> 
>