[Elecraft] KX3 antenna question: Using 'remote' groundplane and random wire

[Jim Brown]

On 8/26/2012 5:34 PM, Andrew Moore wrote:
> Essentially what I want to do is to run the signal from the shack out to
> the trailer and have the radiator and ground plane "start" (and split off)
> there.  However, I'll definitely need the tuner in this scenario, so will
> having the tuner be located 100 feet before the split throw it all off, or
> introduce imbalances along, say, a coax run from the shack to the trailer?

The coax WILL add some loss, and how much loss will depend both on the 
coax and on the degree of mismatch. HOWEVER -- the additional loss due 
to mismatch is often much less than many believe. There's an excellent 
graph in the ARRL Handbook that shows this.

Some suggestions. First, ALWAYS use BIG coax to minimize the loss. You 
don't need a premium coax -- a decent RG8 with a robust copper braid 
shield is fine. Second, for both uses of the antenna, I would run coax 
from the rig to the aluminum frame at the point of connection, and make 
the shield the connection between the rig and the frame. Then simply put 
in a decent coax switch to change between the two operating positions.

Third, once the coax to the house is hooked up, check the VSWR without 
the antenna tuner, then use the graphs in the Handbook to first 
translate the VSWR reading in the shack to the actual VSWR at the 
antenna, then use that value of VSWR to see how much additional power is 
lost due to the mismatch.  If the loss is particularly high on any band 
due to a really bad match, tweak the length of the antenna to improve 
it.  Most really bad matches with a long wire are caused by an antenna 
that is very close to an exact multiple of half-wavelengths, or by a 
dipole that is very close to an exact multiple of a wavelength.  That's 
where the 44 ft vertical came from.

73, Jim K9YC