[Elecraft] KX3 12kHz audio spike

[Jim Brown]

On 8/6/2013 8:49 PM, David Gilbert wrote:
> Currents most certainly do not flow uniformly in ground planes, and 
> coupling effects can be real whenever significant gain is involved. 

Actually, what happens is that a trace above an ideal "ground plane" 
(the ground layer)  forms a transmission line, with the return current 
flowing in the ground plane directly below he trace -- UNLESS the ground 
plane below the trace is broken, for  example, by the circuit board 
layout guy realizing he left something off the main layer, and putting 
on the ground layer instead. In which case there is no longer a 
transmission line, the return current flows wherever it can. inductance 
is added to the path, which causes magnetic coupling to other circuits, 
and it forms an antenna, so it can radiate, into other circuitry, or 
outside the box, or both.

So the RF current in a ground plane is VERY well behaved and 
predictable. The problems arise when the PC layout guy doesn't 
understand the function of the ground plane, and that it CANNOT be 
interrupted without consequences. Like zipper noise on tuning in the K3.

73, Jim K9YC