[Elecraft] KXPA100 Mobile Operations -- Power Output

[Jim Brown]

On 1/12/2014 10:26 AM, Matt Zilmer wrote:
> Wiring to the
> KXPA100 is 8 AWG, with two "transfers" to APPs at a relay enclosure
> for power control in the trunk.  The source is the Civic's battery.
> The KXPA is located in the trunk.

Several thoughts about this. First, noise pickup on the power wiring 
will be greatly reduced by making it twisted pair. Second, unless the 
SWR is REALLY high, much less power will be lost in coax than in the DC 
wiring. Third, ALL of this wiring should have common mode chokes on it 
to further minimize noise pickup and RFI.

My strategy would be to locate the amp based on convenience, on making 
the DC cable shorter, and on the practicality of paths for routing the 
needed wiring.

I would use the best quality coax I could fit into the available wiring 
routes. This is an application for the best quality transmitting coax 
with a heavy copper braid shield.  Remember that the shielding provided 
by coax depends upon a shield that has very low resistance and very good 
uniformity.  Belden 9258 would be a great choice -- it's a RG8X form 
factor (0.242-in o.d.), with #16 stranded copper center and a 95% copper 
braid shield.

Finally, there is probably little benefit to bonding the radio or the 
amp to the frame of the vehicle. Thanks to the excessive application of 
paint and the use of lots of non-metallic parts, chassis bonding of 
modern vehicles is flaky at best, and a train wreck at worst (it is in 
my 2006 Toyota big SUV). Indeed, one of the major challenges in a modern 
vehicle is finding enough conductive structure to form a counterpoise 
for an HF antenna.

73, Jim K9YC