"Rich Grise" wrote in message
news
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?

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?

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

Thanks,
Rich


You probably don't need a program, just a decent text book that covers the
topic adequately, which, undoubtedly is what the program writers worked
from, and they might not have got it right! 'Antennas' by John Kraus
contains enough detail to make a start and it's probably more general than
someone's program which might involve specific choices of some parameter
values. So my recommendation would be to find a technical library that
offers access to non-members and send yourself to Log-Periodic School as you
put it. The IET library in London does this, for free. Do you have an
equivalent institution (e.g. IEEE), or a local university that covers
electronic engineering? You might be surprised how much access you can gain
to libraries to which you have contributed through taxes, or which need to
maintain an 'altruistic' public appearance.

The pyramidal form has greater aperture in the vertical plane for all but
the highest frequencies. It behaves like a vertically-stacked pair of
Log-Periodic Dipole Arrays and achieves a bit more gain. Its pattern in the
vertical plane is consistently sharper over a range of frequencies because
of the vertical taper, but it is a bit more difficult to design. Not all
'wideband' UHF antennas are based on the LPDA - some are Yagi-Uda arrays
designed using NEC and its derivatives, achieving a useful compromise
between bandwidth, gain, and pattern shapes. But if you want to include
channels below 21 as well as the UHF band, with consistent directivity, then
LPDA is probably the only way to go.

Chris