Oil on transponder antenna

wrote:


Clean oil is an insulator.

An oil film with who knows what gunk in it is not such a good insulator.

So, if you change the oil on your antenna regularly...

Nevertheless, I stand by my statement.

In order for dirty oil to effect the transmission, it would have to
carbonize the oil into a conductive track shorting across the insulator
at the base of the monopole. The peak power output from the transponder
is about about 250W, which puts about SQR(250*50)=~110V across the
antenna base.

A little dirty oil will not arc over at 100V!

MikeM

A film of oil with some dirt attached is still transparent to the RF.


HOWEVER if you wipe the antenna that is attached to a thin skinned
aircraft you will MOVE the antenna slightly. Maybe just enough to
restore connection in the rusty connector joint or the broken solder
joint.
Wiping works just not for the reason stated.
JF

On Mon, 03 May 2004 17:49:46 -0600, mikem wrote:



wrote:


Clean oil is an insulator.

An oil film with who knows what gunk in it is not such a good insulator.

So, if you change the oil on your antenna regularly...

Nevertheless, I stand by my statement.

In order for dirty oil to effect the transmission, it would have to
carbonize the oil into a conductive track shorting across the insulator
at the base of the monopole. The peak power output from the transponder
is about about 250W, which puts about SQR(250*50)=~110V across the
antenna base.

A little dirty oil will not arc over at 100V!

MikeM

mikem wrote:


wrote:


Clean oil is an insulator.

An oil film with who knows what gunk in it is not such a good insulator.

So, if you change the oil on your antenna regularly...

Nevertheless, I stand by my statement.

In order for dirty oil to effect the transmission, it would have to
carbonize the oil into a conductive track shorting across the insulator
at the base of the monopole. The peak power output from the transponder
is about about 250W, which puts about SQR(250*50)=~110V across the
antenna base.

A little dirty oil will not arc over at 100V!

MikeM

The oil doesn't have to carbonize, nor does it have to arc over to
effect the antenna.

The gunk caught in the oil only has to be lossy at 1 Ghz which most
materials are.

Old melmac dinnerware (the newer stuff seems to be better) would
catch fire in a microwave on occasion because the stuff was so lossy
at microwave frequencies. Melmac is a good insulator at DC.

That would more likely show up as reduced range on the transponder unless
the gunk was lossy enough to start carbonizing the oil, which I doubt
would ever happen unless it got really thick (in which case you need
to look at how you preflight).

As someone else pointed out though, wiping the gunk off is a likely
source of problems if you don't use a gentle touch on those little
rod antennas.


--
Jim Pennino

Remove -spam-sux to reply.

wrote:

The oil doesn't have to carbonize, nor does it have to arc over to
effect the antenna.

The gunk caught in the oil only has to be lossy at 1 Ghz which most
materials are.

I cant imagine that a little bit of dirty oil could attenuate the
signal by more than a db or two. If your transponder is so anemic
that a db would make a difference, you got more serious problems...


MiKeM