[TenTec] Audio Hum on Omni-VII

[Jim Brown K9YC]

On Wed, 17 Sep 2008 22:32:00 -0500, Dudley Hurry wrote:

>You have a ground loop to the laptop..  I bet that you will lose the hum 
>if you break the ground from the radio to/from the laptop sound card..   
>Better isolation from the radio to the sound card.  

>You might even try an extra ground from the laptop to station ground,  
>but it is most likely a audio loop,  isolation transformers should take 
>care of it.. 

I'm an audio systems design consultant and consultant on EMC in audio 
systems (that is, hum, buzz, and RFI). There is much misunderstanding 
about the unbalanced interconnection of ham gear. Much of what is written 
about it is WRONG, including in some ARRL publications. You do NOT need 
"isolation," you need simple BONDING between the laptop and the radio. 

To see what's REALLY going on with your hum and buzz, and to fix your 
problems without a transformer and using nothing more than plain ordinary 
copper wire, see 

http://audiosystemsgroup.com/HamInterfacing.pdf 

and the Chapter on Solving Problems in the Shack in 

http://audiosystemsgroup.com/RFI-Ham.pdf

73,

Jim Brown K9YC
Audio Systems Group, Inc. 
Chair -- AES Technical Committee on EMC