[TenTec] Even MORE on vertical antennas!
Tue, 3 Sep 2002 09:42:08 EDT
Faraday rotation causes radio signals to "rotate" from horizontally polarized
to vertical and back, more or less continuously. Particularly over a
multi-hop path. Therefore it's not uncommon to find a station coming in quite
strongly on a vertical antenna and not be workable on a beam. Terman's Radio
Engineering makes that situation quite clear for those interested. It also
makes it clear that those who omit a decent vertical from their antenna
arrays are missing some easy Q's.
And speaking of cracking a book, the 4th edition of the Radiotron Designers
Handbook has a very revealing chapter, written by one of the real pioneers in
radio propagation, on antennas. As he points out, a mismatched antenna
reradiates most of the signal it intercepts. Therefore an antenna with a
serous mismatch at the feedpoint is a poor performer on both transmit and
recieve. While recievers commonly have more "excess gain" than transmitters
have excess power output there are limits to everything.
For a little more book cracking I notice the latest ARRL Handbook lists the
SWR of a 100 foot dipole at 50 feet. The two foot difference between that and
a G5RV is essentially trivial, as a few minutes with EZNEC or another antenna
modeling program will show. And even casual consideration of the data will
show why a G5RV is not the all band wonder wire some old hams tales make it
out to be.
I have seen battered but servicable copies of both Terman and Radiotron
Designers handbook (the fat red backed version, not the slimmer black 3rd
edition) at hamfests for a few bucks each. They make invaluable additions to
73 all Pete Allen AC5E