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.