"Rob Turk"
shared these priceless pearls of wisdom:

-"Jim Weir" wrote in message
.. .
- Are you guessing on this, repeating an OWT, or do you have first hand hard
-data?
-
- Jim
-
-
-As a licensed ham operator

Jesus. A ham operator? Those are the credentials you come to the table with?

Amateur radio extra, first licensed in 1959. First 'phone with radar
endorsement, 1960. BS-Physics (Microwave option) 1967. MSEE CGS 1983, RF
option. Pacific Southwest Airlines (1963-1967) avionics and radar technician.
Teledyne Ryan Space Systems (1967-1973) Microwave Antenna Engineer. Founder and
CEO RST Engineering, with a world class reputation for hidden antennas in
nonconductive structures (1973 --) with approximately fifteen THOUSAND operating
antennas in plastic/wood/fabric aircraft including one hanging in the
Smithsonian.


I have sufficient experience with frequencies
-around 1200 MHz.

How long has it been since you fell off the turnip truck, feller? The ham bands
at 33 and 23 cm are 10% or so away from the transponder frequencies. Not too
far away, but far enough.



Those don't like their antenna's shielded by wet or painted
-surfaces.

First, the plural is "antennas", not the possessive. In the second place, this
is the first mistake of fact so far. That is just horsepuckey. Wet and paint
won't make squat for difference. And I've done and retained the engineering
data that says so.


Transponders are just over 1000MHz

1030 and 1090 to be exact. Betcha can't tell me without looking which one is
transmit and which one is receive.



, it's reasonably safe to assume
-they are equally influenced. I'm not saying it will never work (fwiw, GSM at
-900MHz works in-door), but I do want to caution people that there are many
-variables involved that could make it not work.

Yada, yada yada...


-
-Contrary to COM signals (118-136MHz) you can't use just any CB or VHF SWR
-meter to check out if the antenna matches at these frequencies. With the
-transponder sending out pulses of 200+ Watts I wouldn't want to gamble
-having a bad SWR and seeing that power end up ruining the transponder stage.
-Better be safe and put the $22 antenna where it belongs; Outside.


Izzat a fact? Then I guess I'd best trash my $50k worth of RF antenna test
equipment, because I surely wouldn't want to gamble my transponder on brothers
Hewlett and Packard's equipment and the results derived therefrom.

By the way, do the math before you post. That 200+ watts of transponder power
is peak pulse power. If you go through the calculation, you find that the
transponder output stage is running about 5 watts CW averaged over a couple of
seconds or so.

Now, to repeat what I've been telling my colleagues building airplanes for the
last 30 years...put the transponder antenna inside the plastic with a round or
(better yet) octagonal ground plane, shield the sensitive parts of your anatomy
with tinfoil, and go for it.

Jim


Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com