Wanted: Transponder antenna

Where or how did you come up with 8 foot? References Please

"Paul Lee" wrote in message
om...
AFAIK the tranponder antenna should be 8+ feet away from warm bodies.

"Rich S." wrote in message
...
"Paul Lee" wrote in message
m...
There is nothing wrong with the $22 one. Only for fast birds,
you may want an aerodynamic shaped one.
Composite projects can even build the $22 jobs into wings, etc.

Hey! Don't forget us wood and fabric types. I was going to install mine
under my seat, but then I thought about possible radiation effects on
the
family jewels. I mentioned this to my wife who poo-pooed my concern. So
I
put it under her seat.

Rich S.

Man, I didn't intend to start a fight...

I think I'll just buy the TED from AS&S; they're $19.95 in their on-line
catalog. I'll need other stuff, so the S&H won't hurt too bad.

Thanks RAH denizons for the assist!

Got one half of the 'boot' cowl cut, drilled, smoothed last night. I was a
bit dismayed by the un-evenness from the shears (regular scissors-type,
compound lever), but a lot of the waviness went away as I de-burred the edge
with 320 sandpaper. It looks quite nice.

Jon B.

"Cy Galley" wrote in message
news:Ke6xb.315272$Fm2.330421@attbi_s04...
Where or how did you come up with 8 foot? References Please

"Paul Lee" wrote in message
om...
AFAIK the tranponder antenna should be 8+ feet away from warm bodies.

"Rich S." wrote in message
...
"Paul Lee" wrote in message
m...
There is nothing wrong with the $22 one. Only for fast birds,
you may want an aerodynamic shaped one.
Composite projects can even build the $22 jobs into wings, etc.

Hey! Don't forget us wood and fabric types. I was going to install
mine
under my seat, but then I thought about possible radiation effects on
the
family jewels. I mentioned this to my wife who poo-pooed my concern.
So
I
put it under her seat.

Rich S.

"Paul Lee" wrote in message
m...
There is nothing wrong with the $22 one. Only for fast birds,
you may want an aerodynamic shaped one.
Composite projects can even build the $22 jobs into wings, etc.


You may not want to do that. It works for COM but may not work for
transponders. They work on pretty high frequencies (around 1000MHz) and it
doesn't take much to shield such signals. The composit may not be a problem,
but your paint or even wet conditions may stop the signal from getting out.

Rob

Are you guessing on this, repeating an OWT, or do you have first hand hard data?

Jim



"Rob Turk"
shared these priceless pearls of wisdom:

-You may not want to do that. It works for COM but may not work for
-transponders. They work on pretty high frequencies (around 1000MHz) and it
-doesn't take much to shield such signals. The composit may not be a problem,
-but your paint or even wet conditions may stop the signal from getting out.
-
-Rob
-



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

Jim

The Radom's we used in military were transparent to the radar
frequencies. You couldn't just take a can of Krylon and paint them. If
damaged, was a special way of repairing.

There must be data available on effect of glass, cloth and paints,
etc., on RF transmission/reception?

I haven't taken time for a Google search but might be something amoung
Radoms, RF attenuation, etc

Hughes Aircraft, who made the fighter radar I used, might have some
attenuation figures someplace if you can get to the right person.

Have a good Turkey day out there in the land of Fruits and Nuts G
..

Big John

Know you didn't start thread but others will read this post and thread
will go on and on and on...............

On Wed, 26 Nov 2003 09:20:27 -0800, Jim Weir wrote:

Are you guessing on this, repeating an OWT, or do you have first hand hard data?

Jim



"Rob Turk"
shared these priceless pearls of wisdom:

-You may not want to do that. It works for COM but may not work for
-transponders. They work on pretty high frequencies (around 1000MHz) and it
-doesn't take much to shield such signals. The composit may not be a problem,
-but your paint or even wet conditions may stop the signal from getting out.
-
-Rob
-



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

Big John
shared these priceless pearls of wisdom:

-Jim
-
-The Radom's we used in military were transparent to the radar
-frequencies. You couldn't just take a can of Krylon and paint them. If
-damaged, was a special way of repairing.

Exactly my point. There is a tremendous difference between C and X band radar
and low L band transponders. Making generalities such as the prior poster did
without having done the work is the worst sort of conjecture.

The answer is that you CAN take a can of Krylon of the correct mix and paint
them. You can't take just ANY can of Krylon without knowing what you are doing.
And the damage required baking to eliminate entrapped water before you glassed
the damage.

-
-There must be data available on effect of glass, cloth and paints,
-etc., on RF transmission/reception?

Yes, and we did it for Bellanca when we designed their internal antenna system.


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

"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 I have sufficient experience with frequencies
around 1200 MHz. Those don't like their antenna's shielded by wet or painted
surfaces. Transponders are just over 1000MHz, 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.

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.

Rob

"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