[Elecraft] K3: 6M SSB audio hash

[Jim Brown]

On Sat, 7 Jun 2008 01:41:02 -0400, Joe Subich, W4TV wrote:

>That is *NOT* what is happening ... the mic connection does not 
>simply "unbalance" the mic input because one side of the preamp 
>is still not grounded.  What is happening is that the mic is 
>connected to the preamp in a balanced configuration but the 
>shield is left floating on the mic end and tied to the mic 
>return at the transmitter input.  The mic return is then tied 
>back to the chassis through an RF choke (DC return). 

That is an improper connection, a violation of AES48, and a 
violation of good engineering practice. The ONLY proper connection 
of ANY cable shield is to the shielding enclosure. A balanced 
input can take (at least) two forms. One is a transformer. The 
other is a differential input stage. The mic must be connected to 
the two terminals of those inputs, and the shield must go straight 
to the chassis, NOT through a choke. 

You say "What is happening"  -- do you mean that this is wiring 
provided by the W2IHY box? If so, I agree it is really bad. 

>It would be better if the mic return (and shield) was connected 
>directly to the chassis at the mic connector than the present 
>situation 

Absolutely -- it is the ONLY right way to connect a cable shield.

>... but not as good as if the shield were connected to the 
>chassis (usually PTT ground) and the mic treated as a 
>floating/balanced input.  

WRONG! What you have just described is perfect example of a pin 1 
problem, and a VERY common cause of hum, buzz, and RFI. 

See AES48. http://www.aes.org/publications/standards/list.cfm

See also the tutorials on my website. 

http://audiosystemsgroup.com/publish

The pro audio world figured this out long ago. Virtually all EMC 
authorities agree. It's really sad that hams have kept their heads 
in the sand about it. 

73,

Jim Brown K9YC