My search goes on for a simple field antenna system for which the KX1
can get a match on 40, 30 and 20 meters *and* with a good long
feedline so that the antenna can be placed in an exposed location
while the op takes shelter from the sun and wind some distance away.
I'm planning for the ARS Flight of the Bumblebees contest this July -
I want to be able to switch between 20 and 40 over the course of the
event while using a single antenna - with as little feedline loss as
possible.
So here's one I've been playing with lately - it's based on the
"coupled resonator" dipole and was made from pieces of windowed
twinlead I had hanging around in the garage.
I used a 64 foot piece of 16 ga. 450 ohm windowed twinlead (approx. 1
inch spacing between conductors) for the radiating part. One conductor
was opened at the center of the piece and a 40 foot piece of 16 ga.
300 ohm windowed twinlead attached as a feedline. The other conductor
was cut at two points 17 feet each way from the center to create a 34
foot resonator for 20 meters. I just removed a 1/4'' section of wire
to interrupt the conductor (at a point where the webbing was present).
>From what I read in the ARRL Antenna Book topic on this type of
antenna the 1 inch spacing between driven element and resonator isn't
too far off the mark for 16 ga. wire.
Modeling with NEC-Win+ (carefully, the 1'' spacing is getting close)
indicated that the SWR on the feedline would be less than 10:1 on all
3 bands. Although not resonant on 30 meters, with a 300 ohm feedline
the mismatch was on the same order as that for 20 and 40. According to
ZIZL line losses would be well below 1 dB for all 3 bands. This in an
inverted vee configuration with the feedpoint at 35 feet over average
ground. Indeed, once built, and supported by a 32 foot telescoping
fiberglas mast, the KX1 ATU gets a good match on all bands and
operating performance seems much better than the speaker wire doublets
I've used with their lossy feedlines.
But what I really like about the antenna is that since it is all
windowed twinlead with copper plated stranded steel wire it's strong,
tough as nails and easy to handle. It is a bit on the heavy side, but
maybe worth the extra effort to hike it up the mountain for the
contest.
Any other Bumblebees on the list using a KX1 this year? If so, what
antennas do you plan to use?
Bob NW8L
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