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



Roy Lewallen wrote:
Jim-NN7K wrote:
Hi- was searching Amazon , and see several books on Strip Line Antennas
my biggie is: Eznec will take WIRE DIA, and Dial. Constant, and
Thickness in inches of that dialectric. Does this mean that EZNEC is
useable to substrate material (G-10, Teflon, ect) to model Printed
Circuit antennas?

No.

. . .

Roy Lewallen, W7EL

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

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

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

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

On Wed, 27 Aug 2008 09:34:38 -0700, Jeff Liebermann
wrote:

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.

No, I can't. Neither EZNEC or 4NEC2 will model dielectrics.

Also, this might be useful:
http://www.antennex.com/shack/Feb06/lpcad.html
LPCAD 3.0 will generate an NEC file that can be analyzed by your
favorite modeling program.

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

I routinely use EZNEC to design antennas printed on a substrate. I do
the basic design then apply a fudge factor to the conductor width and
length derived from comparisons between model results and measurements
of real antennas. Final designs usually take some adjustment even at
that. However, I haven't tried this for any antenna that depends
strongly on coupling between elements, such as a Yagi, because the
mutual coupling will also be affected by the substrate and won't be so
easy to approximate. In the case of a log periodic, I'd adjust the model
transmission line to try and get the same Z0 and velocity factor as the
line on the substrate, which you might have to determine by measurement.
That would help, but you'd still be lacking accurate mutual coupling
information. At best, I think, a model would get you in the ballpark,
with a final design requiring some tweaking.

Roy Lewallen, W7EL

On Wed, 27 Aug 2008 10:22:19 -0700, Roy Lewallen
wrote:

I routinely use EZNEC to design antennas printed on a substrate. I do
the basic design then apply a fudge factor to the conductor width and
length derived from comparisons between model results and measurements
of real antennas. Final designs usually take some adjustment even at
that. However, I haven't tried this for any antenna that depends
strongly on coupling between elements, such as a Yagi, because the
mutual coupling will also be affected by the substrate and won't be so
easy to approximate.

I once tried scaling a similar antenna for a PCB dielectric and ran
into that problem. I had G10 on one side of the elements and air on
the other, each with its own dielectric constant. Another version
used glass as a substrate. I made a simple breadboard for testing and
found that a good first guess was the geometric average (sqrt of the
sum of the squares) of the dielectric constants. However, when I
actually built the antenna, I had to do considerable tweaking and
guesswork. It's been many years, but I don't think my models and
reality ever agreed.

I also tried to use MSTRIP40 for modeling a dipole array on a PCB.
http://rze-falbala.rz.e-technik.fh-kiel.de/~splitt/html/mstrip.htm
It's intended to do patch and panel antennas, and works well for
those. It can also do a dielectric sandwitch, which might be handy.
However, when I tried to do a simple dipole array, I got bizarre
results, probably due to some mistakes on my part. A single dipole
works fine (it's supplied as a sample file), but I just couldn't get
arrays to work. I just noticed there's a later version available, so
I may try again. However, I'm playing vacation this week so it will
have to wait.

In the case of a log periodic, I'd adjust the model
transmission line to try and get the same Z0 and velocity factor as the
line on the substrate, which you might have to determine by measurement.
That would help, but you'd still be lacking accurate mutual coupling
information. At best, I think, a model would get you in the ballpark,
with a final design requiring some tweaking.

Did you notice the odd patches at the ends of the elements in the
photographs?
http://11junk.com/jeffl/antennas/Sinclair%20SRL441-2P/index.html
Methinks Sincair may have also done some tweaking.

Thanks for the hints.

Roy Lewallen, W7EL

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

Thanks folks Got me curious about adapting this to 1296, or 2404
MHz for quick and dirty antenna to use in contests! tho its an
interesting design, by the time you create this, feed this, and with
the loss's envolved, probably NOT worth the effort! An interesting
use of PC material, non -the-less ! Maybe the Log Periodiotic is less
critical to Board Xc, and Spaceing, then other antenna types? But,
then the (stripline) feedline loss's alone would probably cancel any
gain from the antenna. Again folks , thanks!
When I start thinking- it gets Dangerous out there!

Jeff Liebermann wrote:
On Wed, 27 Aug 2008 10:22:19 -0700, Roy Lewallen
wrote:

I routinely use EZNEC to design antennas printed on a substrate. I do
the basic design then apply a fudge factor to the conductor width and
length derived from comparisons between model results and measurements
of real antennas. Final designs usually take some adjustment even at
that. However, I haven't tried this for any antenna that depends
strongly on coupling between elements, such as a Yagi, because the
mutual coupling will also be affected by the substrate and won't be so
easy to approximate.