[Elecraft] K3: 6M SSB audio hash

[Jim Brown]

On Mon, 9 Jun 2008 00:51:17 -0400, Joe Subich, W4TV wrote:

>By the way, I measured the resistance from the Foster to ground 
>lug on my K3 with the power off - it is about 0.5 ohms.  

What's a Foster?  Is that the proper name for the front panel mic 
jack? If I carefully zero my trusty Fluke 8060A on the lowest R scale 
(that is, short the probes, then set REL) I measure 0.01 - 0.02 ohms 
from the shell of the front panel mic jack to the SO239 for ANT1. This 
is with the power off. Same value, +/- 0.01 ohms to the ground lug. 

>There is 
>something strange going on when I turn on the power and have anything 
>connected to the "Aux" (+12 V) Power output.  I will need to do some 
>more research to figure out what is going on. 

Yes. With the power on, and the radio in RX mode, there is a small DC 
gradient from one part of the chassis to another. I can see anywhere 
from 0.3 to 5mVDC measuring variously between the front panel mic jack 
and the ANT1 SO239, the ground lug, the front panel mic jack, and the 
daughterboard coax connectors! These values float around a bit. If you 
try to measure resistances between these points with the power on, the 
meter can either increase or go negative, depending on which way you 
connect the probes. :) 

That's not at all surprising -- ohm meters are calibrated for un-
energized circuits. Although the resistance of the shielding enclosure 
is small, it isn't zero, so there's some IR drop across it. If we 
believe the meter inside the K3, the TOTAL current from the power 
supply is about 800 mA. That's a worst case number for the current on 
the chassis.  

73,

Jim