Re: More antenna questions

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From: L. B. Cebik (cebik@utkux.utcc.utk.edu)
Date: Wed May 08 1996 - 07:41:45 EDT


Brian,

First, you are correct that the highest current in a quarterwave vertical
is at the base feedpoint and in a horizontal dipole it is at the center,
no matter where along the half-wavelength piece of wire you feed it.

Which is better? That depends on a lot of factors. Verticals are used
by many folks who cannot get 100' towers in the air because, when
well-installed with a ground plane of many many wires, they can be
efficient and radiate at lower angles--hence good for long skip paths.
Due to part of the energy being reflected from the ground, the radiation
from a dipole has an angle of maximum energy that varies with the antenna
height. If you can get the antenna up 1 wavelength (35' on 10 meters, 70
on 20, etc.) the angle of max energy is about 14 degrees. Sounds a
little problematical for 80 and 40 meters, where the angle is high, but
the shorter skip for domestic contacts likes that higher angle.

Ground planes and efficient operation of verticals can be tricky, so for
home brew purposes, one of the best starter antennas is a dipole cut for
80 meters (or for 40, if the yard is small), mounted as high and secure
as possible, fed with 450-ohm parallel feedline to an antenna tuner.
This particular antenna is sometimes called a center-fed Zepp and
performs quite well on all bands, with the antenna tuner providing a
match to the transceiver.

If you are limited in space, consider one of the half wave verticals,
such as made by GAP or Cushcraft. Since they use professionally designed
loading techniques, they require no experimentation to run, and since
they are half-wave verticals, they do not require ground planes--just a
few wires that some call a counterpoise. They ain't cheap, but as
commercial antennas go, they are not expensive. Another alternative for
a vertical is one of the quarter wavelength verticals up on the house
roof, with radial wires (ground plane) following the slope of the roof.
Butternut and a number of other companies make some good trap verticals
suited for this application.

In the beginning, avoid loading schemes. Loads create areas of the
antenna that do not radiate, and most loading devices have power robbing
losses. (Even the verticals noted above have losses due to loading
schemes.) So, you can get your 5' antenna to work, but it will not give
anywhere near the performance of a full size antenna. In an emergency,
of course, load up any old piece of metal and use it as an antenna--it
will work to some degree. But in general, after analyzing what your
space can hold, what your budget will tolerate, what you can and are
willing to maintain, and what the family will put up with, put up the
highest, most full size antenna possible. Later, when you have gotten a
good bit of experience using antennas under your belt, you can experiment
with short antennas, loaded in various ways.

If you live in an apartment and must have a hidden, low, or short
antenna, then, of course, life is one antenna experiment after another.
If you have a yard and there are no restrictive covenants blocking you,
then the best course may be to set up a good basic antenna. When it is
working, raid the radio stores and the hardware stores for materials to
experiment with antennas--there is always much more to learn--enough for
several lifetimes.

Hope this advice, based on 40+ years of experience, has at least one
useful idea in it for you.

-73-
LB, W4RNL

 L. B. Cebik, W4RNL /\ /\ * / / / (Off)(423) 974-7215
 1434 High Mesa Drive / \/ \/\ ----/\--- (Hm) (423) 938-6335
 Knoxville, Tennessee /\ \ \ \ / / || / (FAX)(423) 974-3509
 37938-4443 USA / \ \ \ \ || cebik@utk.edu
  QRPARCI 2572 G-QRP 7203 CQC 125 NEQRP 347 NORCAL 1111 MIQRP 1432
   NWQRP 401 ARRL Life: Educational Advisor QCWA 13211 10-10 41159


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