[Elecraft] Serial Port on K3

[Jim Brown]

On 2/27/2012 8:48 PM, N4CW at aol.com wrote:
> So, is the K3 serial port supposed to crap out when the rig's voltage
> supply isn't optimum?
>   

Several questions.  First, how are you powering the rig?  Two wires 
straight to the battery?  What conductor size?  How long? Did you have 
two wires running to the battery, or were you using chassis as return?  
The latter is a recipe for disaster.

  How were you powering the computer?

What was the "good antenna?"  Was it a mobile antenna or an antenna 
rigged separately from the vehicle, like a dipole strung in trees?  
Thanks to paint between sections of the body, the chassis bonding in 
many cars ranges from awful to non-existent, and antennas attached to a 
car use the chassis as return for antenna current.  This current can 
wreak havoc with any electronics in the vehicle.  Even a ground-mounted 
vertical close to the vehicle can do that too.

What was the serial cable? Was it twisted pair or parallel wires inside 
a shield? Parallel wires inside a shield are very subject to the strong 
magnetic fields produced by antenna current.  Twisted pair provides FAR 
better immunity from RFI.  See

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

for details of how to build a serial cable with far better RF immunity, 
and other advice on avoiding RFI problems in a mobile installation. 
There's also detail about that cable in 
http://audiosystemsgroup.com/HamInterfacing.pdf

73, Jim Brown K9YC