[Elecraft] K3 Line In hum

[Jim Brown]

On Tue, 07 Jul 2009 13:13:57 -0400, Jack Smith wrote:

>Another alternative is to replace the transformers with shielded 
>versions, assuming space on the PCB is available and a shielded 
>transformer with the same electrical specifications and footprint 
is 
>available.

Or simply eliminate the transformers. They are totally un-necessary 
if you do the simple chassis bonding shown in my Ham Interfacing 
tutorial. 

http://audiosystemsgroup.com/HamInterfacing.pdf  

More stuff, in words, in  

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

See the chapter on Solving Problems In The Shack. 

Another thing to try before digging into the rig. If Elecraft has 
followed my recommendation and made TXEQ work on the LineIn, you can 
Use TXEQ with maximum cut on the two lower frequency bands. This is 
good engineering practice to maximize communications audio quality 
anyway, and it should suppress 50/60 Hz by about 20 dB (15dB for the 
lowest filter, plus a few more dB from the skirt of the next highest 
filter). 

This problem with magnetic field susceptibility is well known. My 
neighbor, K6XX (who as it happens also works part time as an 
engineer for Elecraft) has so much magnetic coupling to his K3 from 
a big power supply that it regenerated to 500W when he tried using 
the LineIn for RTTY.   

73,

Jim Brown K9YC