Fan-tenna... An antenna made from a fan?
Did you ever look at a broken household item and think
'I can't throw this out, there just must be some use for it in my ham shack'!
That was the case when our fan gave up the ghost one summer. The more I looked
at the metal cage of that fan, the more it started to look like the perfect
radial system for some future two meter ground plane antenna.
Some quick figuring (234/Frequency [MHz]), showed that if the cage radius
is anywhere near 19 inches, it would make a 'fan-tastic' ground plane.
As it turned out, my cage had a smaller diameter, in fact it was only about
10 inches, but I went ahead with the project anyway.
In an effort to create an easy to build, not to mention cheap,
antenna, I decided to raid the hall closet to confiscate an old wire hanger
to use as the vertical portion of the ground plane. I cut the wire a bit
long to leave plenty of room for adjusting to a 1 to 1 SWR. With the help
Bob (N3LSS), and his 2 meter hand held, we cut and trimmed, and ended up
with a textbook 19.25" vertical radiator and a perfect match.
Construction is extremely simple. First you'll need a connector, to properly
mate with the one on the end of your coax. I used an SO-239 connector from my
junk box. Insert the connector through the center of one side of the fan cage.
My fan cage conveniently separated into two halves and provided easy access
for mounting the connector.
If the center section of your cage is plastic, be sure to attach a jumper
from the connector to the metal portion of the cage.
Solder the coat hanger to the connector.
Lastly, attach your coax after
routing it through the back side of the other cage half.
If you like to tweak and prune, start with a vertical length of
about 21 inches. Cut off only 1/4 - 1/2 inch at a time! If you don't have
access to an SWR bridge for the two meter band, just cut the whip to 19 1/4
inches and your match will be very close.
If outdoor use is anticipated, I'd suggest using an aluminum rod in place of
the coat hanger in order to survive the winds.
Although a 19 inch radius cage is optimum, as this design shows, a cage
diameter even half that size works so don't bother to try and modify its
length at all.
Pretty 'fan-cy' huh?
But does it work? We are fortunate to have access to a local repeater which
has a unique feature. It provides a voice announcement of your signal
strength into the repeater.
A quick test with the new fan-tenna indoors, in front of a window, and on
the ground floor, provided a better than expected 30 over signal.
Additional tests from the same location, using the
hand held's existing whip, proved that the new ground plane was far superior
and provided an amazing improvement in gain. Yes indeed, this antenna does
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