[Elecraft] K3 going expeditionary

[Jim Brown]

On 8/24/2020 8:17 PM, Clay Autery wrote:
> Side bonus, was that the 12VDC ground plane was so good afterwards, that 
> I have been able to take out a lot of the home run grounds from a bunch 
> of lights, et al... ofsetting weight gain by some bit.

Important fundamental concept, Clay, that I learned in an IEEE EMC 
workshop. DC follows the path of least RESISTANCE. AC follows the path 
of least IMPEDANCE. If there is a transmission line with, for example, a 
chassis in parallel with the transmission line return, above about 1 
kHz, all the return current will be in the transmission line, NOT in the 
lower resistance chassis.

That's because the return patch through the chassis includes a lot of 
INDUCTIVE REACTANCE, which increases in proportion to frequency, while 
the path through the transmission line, if matched, never rises about Zo 
of the line. The whole point of using the transmission line is to reduce 
noise and crosstalk. It's only effect on DC (as compared to the chassis 
path) is to slightly reduce the DCR of the return path by adding the 
transmission line return in parallel. With coax, of course, the shield 
is the return. Wtih 2-wire line, one conductor is the "hot" lead, the 
other the return. AND -- 2-wire line and coax are no different in this 
regard! The KPA500, for example, uses twisted pair for wiring from the 
input coax to the amp input stage.

73, Jim K9YC