Richard Harrison wrote:
Phil wrote:
"If not, what other homebrew antenna will be fine for the purpose?"

I believe Walter Maxwell, W2DU, while working with RCA`s satellite
program, designed quadrafilar helix antennas to communicate with the
birds. Look at their pattern on page 765 of Kraus` 3rd edition of
"Antennas", then compare with patterns shown on pages 763 and 764. The
advantage is clear.

Best regards, Richard Harrison, KB5WZI

Because one of the very important functions of a TV antenna is to reduce
multi-path interference causing fading and ghosting, directionality is
essential. The quadrifilar helix I'm familiar with is a normal-mode
helix; that is, the maximum radiation or reception is broadside to the
helix, and it has an omnidirectional horizontal pattern when the axis is
vertical. That would be a poor choice for a TV antenna. You might,
though, consider an axial mode helix. That's one which has maximum
radiation or reception in the direction of the helix axis. I don't have
any direct experience with them, but believe they can be made fairly
broadbanded. It might be pretty large and cumbersome, though. You should
be able to find design data on the web for an axial mode helix.

Sorry, I don't have the third edition of Kraus yet. Is there really a
fairly directional quadrifilar helix in it? In the second edition, the
quadrifilar helix is described as a normal mode helix, which is my
experience, and the pattern shown in the book of a conventional normal
mode helix resembles that of a dipole as it should. Quadrifilar helices
are commonly used for GPS receivers, where an omnidirectional pattern is
desirable.

By the way, I finally got a copy of Bailey -- I came across a copy the
other day at Powell's Technical Bookstore, for $15!

Roy Lewallen, W7EL

Arrgh! I confused this thread with a recent one asking about UHF TV
antennas. My response wasn't at all appropriate to this discussion.

I agree completely with Richard Harrison, a quadrifilar helix is
probably a good choice for this application.

I sincerely apologize to Richard and other readers for my carelessness
and mistake.

Roy Lewallen, W7EL

Roy Lewallen wrote:

Because one of the very important functions of a TV antenna is to reduce
multi-path interference causing fading and ghosting, directionality is
essential. The quadrifilar helix I'm familiar with is a normal-mode
helix; that is, the maximum radiation or reception is broadside to the
helix, and it has an omnidirectional horizontal pattern when the axis is
vertical. That would be a poor choice for a TV antenna. . .

Roy Lewallen, W7EL wrote:
"I confused this thread with a recent one asking about UHF TV antennas."

I understand. My strugle with TV reflections involved antennas atop the
corporate headquarters. We had to have a perfect color picture in the
executive lounge and there was no cable yet. The founder, chairmman and
CEO was proud of his luxury and toys. We had a lot of signal, but too
many signals due to other skyscrapers around ours. With sharp enough
antennas we were able to clean up the mess. Better a hero than a goat!

I think I was very lucky today. I had typed the previous posting and was
about to hit the send button when the electric power failed. I was sure
it would mean retyping. However, when power was restored, I wert to the
archive and found it in storage. Hooray!

Best regards, Richard Harrison, KB5WZI

Roy Lewallen, W7EL wrote:
"Because one of the very important functions of TV antennas is to
introduce multipath interference causing fading and ghosting,
directionality is essential."

Yes indeed! In an urban invironment that is especially important. I`ve
fought the battle to suppress ghosting and smearing. But, my signal
sources were nearly horizontal and they reflected like billiard balls
from every reflective object they encountered. Reflections were often in
the horizontal plane same as the incident signal.

I would think that shortly after a satellite makes it above the horizon,
the incudent wave`s reflected signals would be headed skyward and be
unlikely to cause much trouble at the receiver. The quadrafilar helix
pattern appears something like a mushroom.

Roy also wrote:
"Sorry, I don`t have the 3rd edition of Kraus yet."

I only recently got it. Now I think it is unfortunate I didn`t have it
on order before it was released. It is crammed with good stuff.

Roy also wrote:
"By the way, I finally got a copy of Bailey ---I came across a copy the
other day at Powell`s Technical Bookstore for $15 ! "

Congratulations! Hope you enjoy it as much as I. His catalog pf various
antennas is without par. His theory is systematic and concise. He must
have been a tremendous asset at Bell Labs.

Best regards, Richard Harrison, KB5WZI

hi,

http://www.cebik.com/wire/turns.html

http://www.cebik.com/vhf/ms2.html