[aprssig] aprssig Digest, Vol 53, Issue 25
Stephen H. Smith
wa8lmf2 at aol.com
Fri Nov 28 20:15:32 CST 2008
Charlie Gallo wrote:
> Good question - I have a similar problem - there is a nasty RF hole to the north of me - with my digi down (which it has been for 1-2 years now)., but in the other say 270 degs I'm just QRM - the question is - put it back up, and fill the hole, or, cut down the QRM? NYC has way too much QRM as it is, it's just that there are holes everywhere, due to hills and man made canyons.
Build or buy a small 3-element yagi or dipole in corner reflector, and
point it in the desired direction. The 3-element yagis and corner refs
are often available in end-mount designs that can clamped to an existing
mast beneath the top and pointed in the desired direction. The small
3-element version of a yagi will have a fat forward lobe approximately
70-90 degrees beam width that can neatly fill in your hole while sparing
the rest of the world.
Another DIY REALLY cheap approach is to build a quagi - one full
wave-length loop and two half-wave straight pieces of rod or wire stock
through the diameter of a piece of PVC pipe. (The standard quagi
designs published show one with 8 elements; just build the first three
elements of this design.) The biggest problem in home-brewing VHF and
UHF antennas is the feed system where the coax attaches. In a quagi,
the driven element is a simple full-wavelength of wire or tubing bent
into a square and directly fed by the coax -- couldn't be simpler.
You can throw one of these together out of #12 or #14 house wire and
PVC pipe in about an hour.
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