Randy Yates wrote:
Hi Folks,

This is my first post to this group. I'm a EE, so I've
had all the theory - now I want to know how these things
work.

I highly recommend that you get a couple of basic antenna texts. Very
few people understand how antennas work, but they're nonetheless free
with advice and explanations. Texts are generally reliable. The _ARRL
Antenna Book_ is about the only book I can recommend that covers the
topic at less than an engineering level. For engineering texts, Kraus'
_Antennas_ is the gold standard. You can find earlier editions at very
reasonable prices. There are, of course, a number of other very good
texts. Be very careful of information you get from the Internet,
including newsgroups.

As a person who develops, sells, and uses antenna modeling software, I
also highly recommend this as an educational tool. I guarantee you'll
learn a lot about antennas by doing some modeling. The free demo version
of EZNEC is available at http://eznec.com, but there are other free
programs available.

Basically, my question is this: how can a a TV antanna
cover, what, 60 MHz to 800 MHz? That's over three octaves,
and if the antenna elements are designed to be a fixed
portion of a wavelength, why does this work over such a
large range?

One answer to your question is that "work" isn't a binary quantity but a
continuum. TV antennas typically work considerably better at some
frequencies than others. They just have to work well enough to provide
an adequate signal to the receiver, and hopefully provide some
directionality to reduce multipath interference. Most are a sort of
combination of Yagi and log-periodic designs, with a lot of tweaking and
trickery. Another respondent mentioned that elements are sometimes bent
into a V shape. This little trick provides an element which has a
bidirectional pattern at two frequencies related by a factor of three --
about the ratio of the high VHF to low VHF channels. Elements naturally
are resonant at multiple frequencies, including frequencies related by a
factor of three.

Good luck with your endeavors!

Roy Lewallen, W7EL