Rich Grise wrote:
My current UHF antenna is a 14" Radio Shack clip lead clipped from the
center of my coax to the venetian blind. I have to hand-adjust it
for the channel, weather conditions, phase of the moon, etc. I can
do this because I can _see_ an indication of signal strength.

Well, with this new Fascist "No More Free TV" crap, I'm gonna need
a real UHF antenna. My budget is exceedingly limited, but I have
a supply of materials (GTAW filler rod, with some coppery-colored
coating, so it solders like a dream, and is as stiff as piano wire)
to build an antenna with.

But I've been searching the web for some weeks now, and I can't
seem to find any kind of formula, except there was this program
I downloaded - LPDA.EXE, which runs on DOS. Unfortunately, it's
in Russian or Polish or Uzbekistani - one of those East Yurp
languages. Here's a screen snap:
http://mysite.verizon.net/richgrise/...rog-Output.gif

Which I went through pretty much by-guess-and-by-gosh - can
anybody read that stuff?

There are a lot of factors I don't know about, like "Tau", and
all of the specific designs on the web are flat - something is
telling me I want one of those pyramid-shaped ones, but I really
don't know the difference (between that and flat) - it's probably
something to do with bandwidth or F/B ratio or whatever.

My local library has no ARRL Antenna Book (!), and did I mention
I have a seriously limited budget?

Interlibrary loan is your answer. Your library may not have it, but
someone else's does.



So, how do I pursue this? It'd be nice to have a program that will
calculate the whole thing for me, but am I dreaming? If I want to
send myself to Log-Periodic School, where should I start?

Looking for a cookbook design, or the theory to do it yourself?


Or, does anyone have a UHF-TV log-periodic design that they'd share? :-)







Thanks,
Rich

On Wed, 19 Nov 2008 16:49:03 -0800, Jim Lux wrote:

Rich Grise wrote:
....
myself to Log-Periodic School, where should I start?

Looking for a cookbook design, or the theory to do it yourself?

Cookbook, if at all possible. Like, element lengths and spacing,
and the angle between the booms - which brings up a question - what
effect does it have when you take a flat L-P and "open it up", like
to a pyramid shape - I was doing a thought experiment with this and
when it's completely "flattened out", (180 degrees between the booms),
it looks like a drum roll please Bow Tie!

Thanks,
Rich

"Rich Grise" wrote in message
news
I was doing a thought experiment with this and
when it's completely "flattened out", (180 degrees between the booms),
it looks like a drum roll please Bow Tie!

I think a bow tie's design is actually motivated more by one of the "standard"
ultra-wideband antenna designs, that of a pair of opposing cones touching each
other at their narrow ends, being translated down into 2D.

"Joel Koltner" wrote in message
...
I think a bow tie's design is actually motivated more by one of the
"standard" ultra-wideband antenna designs, that of a pair of opposing
cones touching each other at their narrow ends, being translated down into
2D.

Standard, indeed; this antenna is known as a biconical. It has excellent
wideband response making it ideal for EMC testing. Most good antenna texts
such as that by Krauss give a detailed analysis of the biconical antenna. I
see no relationship between its design and a fractal design other than both
are wide bandwidth antennas.

The bowtie antenna which Rich and others have mentioned is a "flattened"
form of the biconical. If the bowtie is bent along its major axis, it makes
an excellent wideband driven element for a corner reflector antenna.

73, Barry WA4VZQ

Thanks for the details, Barry... tell me though, then, is a discone just a
biconical with a ground plane used to create the (image of the) missing cone?

"Joel Koltner" wrote in message
...
Thanks for the details, Barry... tell me though, then, is a discone just
a biconical with a ground plane used to create the (image of the) missing
cone?

Yes. It will have less gain than a biconical and the bandwidth is slightly
more restrictive too. But it is much easier to construct!

73, Barry WA4VZQ

"NoSPAM" wrote in message ...

"Joel Koltner" wrote in message
...
Thanks for the details, Barry... tell me though, then, is a discone just
a biconical with a ground plane used to create the (image of the) missing
cone?

Yes. It will have less gain than a biconical and the bandwidth is
slightly more restrictive too. But it is much easier to construct!

73, Barry WA4VZQ


All else being equal, a lossless 'ground plane' type antenna, be it a
monopole developed from a dipole or a discone developed from a biconical
dipole, over an infinite ground plane should exhibit 3 dB _more_ gain than
the symmetrical 'parent' form of antenna. This is because its radiation
pattern is limited to half the solid angle of the parent (e.g. only the
space above the ground plane). Then for a given number of watts fed into
the antenna, the power-flux density must be greater in the region where it
can radiate. In practice, the ground plane isn't infinite so there is some
'undercutting' of the vertical radiation pattern, but the gain should still
be somewhat greater.

The apex angle of the cone in a discone can be chosen to yield 50 ohms
terminal resistance over part of its usable bandwidth, and that angle is
different from the apex angle(s) needed in a biconical dipole for the same
impedance. The usable bandwidth is always limited by the limited
flare-length of the cone(s) and usually also by the accuracy of the apex or
apices where termination is made.

Chris