Foil Antenna on Carbon Fiber

I'm building a carbon fiber airplane and understand that the carbon is too
opaque to radio signals to use antennas inside the carbon. (The wing tips
are E-Glass and come with navigation antennas already installed.) For
communication, marker beacon, and transponder antennas, I'm wondering why I
can't use a foil tape antenna kit to stick foil tape to the outside of the
fuselage skin somewhere on the belly and then cover it with a layer of
E-Glass to protect it? I could use the carbon as the ground plane or build
one inside the fuselage, if the carbon isn't enough.

I heard from an expert that applying the foil directly to the electrically
conductive carbon would be just as bad as applying it directly to aluminum.
That makes sense, so how about I put a nonconductive layer of something
(E-Glass?) between the foil and the carbon?

Thanks,

On Thu, 22 Apr 2004 20:20:35 -0700, "Dennis Mountains"
wrote:

:I'm building a carbon fiber airplane and understand that the carbon is too
paque to radio signals to use antennas inside the carbon. (The wing tips
:are E-Glass and come with navigation antennas already installed.) For
:communication, marker beacon, and transponder antennas, I'm wondering why I
:can't use a foil tape antenna kit to stick foil tape to the outside of the
:fuselage skin somewhere on the belly and then cover it with a layer of
:E-Glass to protect it? I could use the carbon as the ground plane or build
ne inside the fuselage, if the carbon isn't enough.
:
: I heard from an expert that applying the foil directly to the electrically
:conductive carbon would be just as bad as applying it directly to aluminum.
:That makes sense, so how about I put a nonconductive layer of something
E-Glass?) between the foil and the carbon?

I've done it (with a layer of E-glass in between) on a carbon canard
for a NAV antenna and it worked fine. The same antenna worked for
marker beacon, too, but I was told the link budget for the marker is
huge.

But my understanding is that com and transponder are vertically
polarized. Jim?

Dennis

All kinds of things have worked that the theory says shouldn't. People used
to string tinfoil around a room to get better TV reception...Sometimes it
actually worked! But you have to strech antenna theory a bit to explain how.

Here is how the theory says it will work. Most things have "worked" for
someone. Your idea of insulating the foil on the outside of the carbon fiber
should not work very well.

I can't find a simple explaination of this on the web. It's not a simple
subject. It involves Electric fields and magnetic fields in space, In order
to propogate, they must be set up in a certain geometric arrangement.
http://www.chem.vt.edu/chem-ed/light/em-rad.html . That is what an antenna
does.

A ground plane has to be close to right angles to the antenna conductor.
One right behind the conductor will not work well at all, because it doesn't
allow the electric and magnetic fields to both be at right angles to each
other and to the direction of travel.

Having said that, it might be fun to try it, and measure the VSWR. You'll
find that it sucks!






"Dennis Mountains" wrote in message
...
I'm building a carbon fiber airplane and understand that the carbon is too
opaque to radio signals to use antennas inside the carbon. (The wing tips
are E-Glass and come with navigation antennas already installed.) For
communication, marker beacon, and transponder antennas, I'm wondering why
I
can't use a foil tape antenna kit to stick foil tape to the outside of the
fuselage skin somewhere on the belly and then cover it with a layer of
E-Glass to protect it? I could use the carbon as the ground plane or
build
one inside the fuselage, if the carbon isn't enough.

I heard from an expert that applying the foil directly to the
electrically
conductive carbon would be just as bad as applying it directly to
aluminum.
That makes sense, so how about I put a nonconductive layer of something
(E-Glass?) between the foil and the carbon?

Thanks,

"Richard Riley" wrote in message
...


I've done it (with a layer of E-glass in between) on a carbon canard
for a NAV antenna and it worked fine. The same antenna worked for
marker beacon, too, but I was told the link budget for the marker is
huge.

But my understanding is that com and transponder are vertically
polarized. Jim?

Hi Richard,

Thanks for the info that you've actually made a NAV and marker beacon
antennas work on carbon fiber, with a layer of E-glass in between! Maybe
there's hope for this idea yet. But I don't understand what you mean by
"the link budget for the marker is huge."

Thanks,
Dennis

"Ron Webb" wrote in message
...

I can't find a simple explaination of this on the web. It's not a simple
subject. It involves Electric fields and magnetic fields in space, In
order
to propogate, they must be set up in a certain geometric arrangement.
http://www.chem.vt.edu/chem-ed/light/em-rad.html . That is what an
antenna
does.

A ground plane has to be close to right angles to the antenna conductor.
One right behind the conductor will not work well at all, because it
doesn't
allow the electric and magnetic fields to both be at right angles to each
other and to the direction of travel.



Hi Ron,

Thanks for the reply and for the interesting link to the web site. I'm sure
you're right and I figure that there must be some fundamental flaw in my
thinking about this; otherwise everyone with carbon fiber airplanes would
already be doing it since nobody wants a bunch of antennas hanging out in
the airstream.

Thanks,
Dennis

On Fri, 23 Apr 2004 06:48:05 -0700, "Dennis Mountains"
wrote:

:
:"Richard Riley" wrote in message
.. .
:
:
: I've done it (with a layer of E-glass in between) on a carbon canard
: for a NAV antenna and it worked fine. The same antenna worked for
: marker beacon, too, but I was told the link budget for the marker is
: huge.
:
: But my understanding is that com and transponder are vertically
: polarized. Jim?
:
:Hi Richard,
:
:Thanks for the info that you've actually made a NAV and marker beacon
:antennas work on carbon fiber, with a layer of E-glass in between! Maybe
:there's hope for this idea yet. But I don't understand what you mean by
:"the link budget for the marker is huge."

When you're actually using the marker beacon - when you're on final
and it goes off - you're directly over it's transmitter, in line of
sight, and only a few hundred feet away. The transmitter is a pretty
tightly focused beam. So it's hitting you with lots and lots of
power. Your antenna could be absolutely awful and there still more
than enough power to activate your MB.

Your com, though, you want to work when you're not line of sight
(you're on the gruond, behind a hangar, and you want to talk to the
tower) and when you're farther away (50 miles out, and you want to
talk to center.) So every part of the system has to be working as good
as it can.

A foil antenna that you put flat on the bottom of your fuselage would
be better than nothing, but not as good as one that you put vertically
in a glass vertical stab. Would it be good enough? Don't know. Jim
Weir will be back next week, he's the expert on all this.

"Richard Riley" wrote in message
...

When you're actually using the marker beacon - when you're on final
and it goes off - you're directly over it's transmitter, in line of
sight, and only a few hundred feet away. The transmitter is a pretty
tightly focused beam. So it's hitting you with lots and lots of
power. Your antenna could be absolutely awful and there still more
than enough power to activate your MB.


Hi Richard,

Thanks for the clarification; I now understand and it makes sense that the
needs of the marker beacon antenna would be much less than for a com
antenna.

Thanks,
Dennis

"Richard Riley" wrote:
...and only a few hundred feet away. The transmitter is a pretty
tightly focused beam. So it's hitting you with lots and lots of
power. Your antenna could be absolutely awful and there still more
than enough power to activate your MB.

I agree there's more "slop" to work with a marker installation, but
you're overstating the case. A marker rcvr is about 150-200 times
less sensitive than a com rcvr, and the MB's transmitter puts out a
small fraction of the power of even a unicom station.

Some quick math tells me being 1500' above an outer marker is the same
as about 40 miles from a control tower for receiving comm
transmissions. Jim Weir might come up with a different number on
better assumptions, but I think he may agree a marker antenna has to
work much better than "absolutely awful."

Fred F.