[Elecraft] K3 Current Drain When Off

[Jim Brown]

On 10/18/2013 11:45 PM, Bill Frantz wrote:
> When I tried measuring in the negative lead, I found zero amps. The 
> problem is that the grounding system in my station setup bypasses the 
> negative lead, probably in several ways, letting me power the K3 up 
> with no connection to the negative power supply lead at all. 

That suggests that the negative terminal is bonded to the chassis in 
your DC power supply. There are some good reasons to NOT do that, and 
many power supplies are built with DC- not bonded to the chassis.  It 
also suggests that all the gear in your station is properly bonded 
together.

With all equipment bonded together, one might think that the bonding 
could carry DC-, and no "black wire" was needed. That's wrong -- while 
DC follows Ohm's Law, AC current (and RF) finds the path of lowest 
impedance, which includes the loop inductance of a path. So if there 
were no black wire, RF would couple into the resulting loop, putting it 
on the red wire.

What we fail to realize is that parallel wire cable (like the red/black 
glorified zip cord we use for power, and that is sold as speaker cable) 
is a sitting duck for RF. Far better to use twisted pair, which has 
about 30 dB better RF rejection. I've fixed a lot of RFI to audio system 
problems by replacing that zip cord with twisted pair.

73, Jim K9YC