On Wed, 27 Aug 2008 08:26:23 -0700, Jim-NN7K .
wrote:

Jeff Liebermann wrote:
On Tue, 26 Aug 2008 10:05:19 -0700, Jim-NN7K .
wrote:

Thanks- just was curious- while still working had sites with wedge
shaped antennas- one broke its ray-dome - these (Scala?) were on
960MHz , and the antenna itself appeared to be a Log-Periodic ,
on a double sided Printed Circuit board- Just curious as to the effects
on impedence, and element lengths-spacing , as to how this antenna
was designed. Jim NN7K

Would a photo help? This is the guts of a Sinclair SRL441-2P:
http://11junk.com/jeffl/antennas/Sinclair%20SRL441-2P/index.html

Data sheet at:
http://www.sinclairtechnologies.com/catalog/product.aspx?id=962

Yep, Thats the Beast! These used by railroad, for double track
installations, for boxcar readers (Automatic Equipment Identification)
and mounted at ground level, aimed up about 30 degree angle,to read
ID tags.
Thanks, Jim NN7K

We'll, there's not much that I can tell you about the design. It's a
log-periodic antenna built onto a PCB. It's not G10/FR4 and might be
Polysulfone. Like the LPDA acronym suggests, it's nothing but a mess
of dipoles at varying frequencies, which results in lots of bandwidth
and not much gain.

This might help with the numbers:
http://www.changpuak.ch/electronics/lpda.html
Use Frequency 800-1000MHz and 180mm boom length.
It's not exactly the same as the Sinclair LPDA uses staggered
elements.

Other calculators:
http://www.fortunecity.com/skyscraper/jolt/345/LogCalc.html
LPDA Excel Spreadsheet calcs:
http://www.astro.hr/ucionica/radioastronomy/antenna/lpda.zip
Another LPDA calculator (that I haven't tried):
http://www.astro.hr/ucionica/radioastronomy/antenna/lpcad23.zip

More light reading:
http://www.wolfgang-rolke.de/antennas/ant_400.htm
http://en.wikipedia.org/wiki/Log-periodic_antenna

A $40 commerical LPDA for 400-1000GHz.
http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=LPY41

If you want to see the effects of juggling spacing, element count, and
boom length, it's probably best to use an antenna modeling program.
Looks like you have EZNEC, which will work. If you download the 4NEC2
antenna modeling program, you'll also get a mess of example NEC2
files. There's a directory under:
c:\4nec2\models\logper\
with 4 log periodic antennas, mostly for HF. EZNEC can read them. I
can probably conjur my bad guess of a model of the Sinclair antenna,
but I'm playing vacation and would rather be doing something else.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558