On Tue, 4 Jan 2011 22:55:49 -0800, "Ron Hinds"
wrote:


"Richard Clark" wrote in message
.. .

Returning to the deafness above 70cm, this wavelength is verging on
being so small, that it would be a sin NOT to build your own antenna
for those high bands. This is something you can do at the kitchen
table in an evening during commercial breaks.

That sounds like fun! Where do I go to find out more?


Hi Ron,

Antenna design has many variables with frequency (or its inverse with
wavelength) being key among them.

This means, of course, that you must first select the frequency or
band of frequency you want to work (or to listen to).

Second, you would want to set some goal for gain over an ordinary
dipole or monopole (a misnomer as all antennas are dipoler, but this
term is universally acknowledge to informally mean a vertical).
Perhaps a dipole or monopole (vertical) is enough to begin with.

Third, you want to select the polarization you intend to work (or
listen to). This is extremely important for VHF/UHF because its
line-of-sight path is very polarization sensitive. Verticals will
"see" verticals. Horizontals will "see" horizontals. Verticals and
Horizontals will be blind to each other. This is sort of mixing
metaphors where previously I used the term "deaf," it amounts to the
same thing: "cross polarized" signals will NOT WORK. In the VHF/UHF
bands, casual use is vertical polarization; however, for serious DXers
it is often horizontal and that activity is usually confined to DX
bands within the VHF/UHF. By casual use I mean simplex between you
and someone else locally, or contacts through repeaters for greater,
but still local range.

Fourth, height is key to "seeing." And, as you are entering into
experimentation, you want to erect some pole that will be both
securely fastened when erected, but also lowerable so that you can
attach your design and transmission line to it. Here again is the
see-saw nature of design. You will be raising and lowering this more
than once, so plan on it ahead.

Fifth, once you have the first four thought through (if not actually
achieved) you should observe one quality about antenna design: it is
scaleable. This means that if you find an antenna described on the
internet that embodies all of the considerations listed above BUT it
is in the wrong band, then there is a simple solution. An example
will serve to illustrate.

Let's suppose you run across a Discone Antenna design on the internet
(it satisfies your need for multiband application, let's say).
However, the author of the design reveals how it was set up for HF
operation between 60M and 10M (a very do-able design, if somewhat
unwieldy in construction). Your interest is not in HF (suppose), but
rather in VHF. What to do?

The antenna you are considering, but which is too large, is too large
by 10 times. Scaleability in antenna design answers this with: change
the existing design to 1/10th of all physical lengths and widths.

TA DA! A broadband antenna that works 6M to 220MHz with the
characteristics of the original size. What was formerly an unwieldy
size is now more manageable by virtue of scaling.

Just do it.

The same logic applies to more complex designs (and less complex ones,
certainly) that you might see touted on the internet.

Finally - there is no reason to expect that anything you find on the
internet actually works as the author of the page may describe. In
fact, the higher the content of gushing and exhortation, accompanied
with a laundry list of claims, will give every indication of someone
being out to lunch. Check in here for sanity checks. This may
inspire long discussions that ramble through many posters here (so
far, none have been inspired to dip their oar in this thread). This
is the nature of newsgroup activity that often focuses on minutia.
However, from the bulk of response, you will get the general sense.

73's
Richard Clark, KB7QHC