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Fun with antennas



One thing that has done much to keep me out of trouble
lately was a visit to the local hardware/garden store,
where I noticed they were selling bundles of sticks. They
are intended for holding up growing plants in gardens, but
are just the right size (20 mm square, 920 mm long) for
making struts and booms and things for light-duty experi-
mental antennas. These ones are cedar, so they even smell 
wonderful...

So far I've used my techie's armoury (saw, ruler, bundle
of cedar sticks, etc. - thanks to G3RUH for the phrase!)
to build a Lindenblad antenna, and a quadrifilar helix.
Both work. Both look like bad props from a Z grade mad
scientist/monster movie. Both produce huge signals from
low-orbit weather satellites. The Lindenblad has a fairly
deep overhead null in its pattern, but appears to have more
low-elevation gain.

Total investment: very little. Admittedly, it helps to
have assorted roll-ends of coax, twinlead and ladder line
in one's junkbox... :-)

If you're thinking of building a quadrifilar helix, there
is an article in the new ARRL UHF/Microwave Projects Manual,
Volume 2. It's very clear, and one of the few that doesn't
look like something from a topology textbook.

Laura Halliday VE7LDH     "Laisse le vent tout emporter..."
Grid: CN88hk IOTA: NA036     - Foly/Viennet

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