Dave,
Make it a balanced dipole antenna (equal lengths on either side of the
feedpoint) for best efforts in keeping RF off the feedline. The actual
length does not matter a lot, but it should be greater than 80% of the
half wavelength for the lowest band of interest.
Use open wire line or 450 ohm ladder line to feed it down to the point
where it enters the shack - hopefully you can run the feedline
perpendicular from the radiator for at least 1/4 wavelength on the
lowest frequency of interest for lowest radiator to feedline pickup.
Put a good 1:1 current mod choke at that point. See page 29 of K9YC's
RFI tutorial http://www.audiosystemsgroup.com/RFI-Ham.pdf
for instructions on how to construct a very effective current mode choke
- note: a good balun *is* a current mode choke, but many fail to perform
as well as the ones tested by K9YC.
You will need a tuner, and any Elecraft tuner should do the job nicely.
If it does not, then you may have to make some adjustments in the length
of the parallel feedline to see if you can achieve success on all bands
of interest.
You may want to take a look at the Antenna and Transmission Line article
on my website www.w3fpr.com for a bit on non-math theory on antennas.
73,
Don W3FPR
On 10/17/2014 4:45 PM, david beckwith wrote:
Just moved and my K3 needs a new antenna. My only option is to run a wire
antenna over my roof--I have about 110-120 feet to play with and I can get one
end up off the ground 25 feet and the center and other end about 35 feet. Any
ideas? Or references to an antenna group that can help? Thanks Bunches and 73
Dave K6CGE
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