Pinging Jim Wier - X-Ponder Antenna Question

[Bob Chilcoat]

Jim,

Saturday coming back from Georgetown, DE to Somerset, NJ, no one, not Dover,
ACY or McGuire, could receive my transponder. We'd had this problem once
before, and our avionics guy suggested cleaning off the transponder antenna,
which is close enough to the engine on the Archer that it gets oily. It was
really dirty that time, and cleaning it seemed to work, so one of my
partners tried cleaning it again just before taking the plane up after I was
finished with it. He said that just a very small bit of oil came off the
antenna, but he then had no problem at all with the Wilkes-Barre TRSA seeing
him. Again this procedure seems to have worked.

My question is this: Does it seem reasonable that a very small amount of
oil on the antenna can effect transmission that much? Isn't even dirty
motor oil pretty non-conductive? Should we be looking more closely at the
antenna to see if it might have a loose connection that gets jostled from
the paper-towel wipedown?

--
Bob (Chief Pilot, White Knuckle Airways)

I don't have to like Bush and Cheney to love America

[EDR]

In article >, Bob Chilcoat
> wrote:

> My question is this: Does it seem reasonable that a very small amount of
> oil on the antenna can effect transmission that much? Isn't even dirty
> motor oil pretty non-conductive?

Maybe! The filter traps all the big pieces, but the microscopic stuff
that slips through acts like metal plating when it coats the antenna
and reflects those transponder signals back down the coax to the
transmitter final. ;-))

[Jim Weir]

There are a lot of folks who will tell you that blowback engine oil will be an
insulator and not affect the transponder antenna. I have no argument with their
theory that oil is an insulator and cannot affect antenna performance at 1.06
GHz.

However, as they say, boychick, engine oil on the transponder screws up
performance. Like it or not, theory or not, it happens. It matters not whether
or not you believe it, it happens.

Jim




->
->My question is this: Does it seem reasonable that a very small amount of
->oil on the antenna can effect transmission that much?
Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

[Bob Chilcoat]

Thanks, Jim,

This got discussed in RAO, too, and there was no consensus. Sort of like
the downwind turn, only truth is harder to find. I suspect that at 1+ GHz,
dirty motor oil may well have a significant conductivity, but who knows
without measuring it. I'm still going to check out the antenna and it's
cabling, but I was curious. Perhaps our 1600-hour engine is throwing off
more oil these days.

--
Bob (Chief Pilot, White Knuckle Airways)

I don't have to like Bush and Cheney (Or Kerry, for that matter) to love
America


"Jim Weir" > wrote in message
...
> There are a lot of folks who will tell you that blowback engine oil will
be an
> insulator and not affect the transponder antenna. I have no argument with
their
> theory that oil is an insulator and cannot affect antenna performance at
1.06
> GHz.
>
> However, as they say, boychick, engine oil on the transponder screws up
> performance. Like it or not, theory or not, it happens. It matters not
whether
> or not you believe it, it happens.
>
> Jim
>
>
>
>
> ->
> ->My question is this: Does it seem reasonable that a very small amount
of
> ->oil on the antenna can effect transmission that much?
> Jim Weir (A&P/IA, CFI, & other good alphabet soup)
> VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
> http://www.rst-engr.com