Andy wrote:
Tim Mara wrote:


Also I note that you say you have a transponder antenna mounted vertically
on the top of the fuselage.........this is also not a proper installation
since transponder antennas are intended to be directed toward the ground
(radar receivers) and Carbon fuselages will block or even absorb signals
rather than reflect them away as a proper ground plane does.

If there is a choice of being seen either from above, or from below,
I'll take above every time. I'd far rather be seen on the TCAS of an
airliner that is descending through cloud into me than be seen on a
controller's screen.

Of course, if the controller could see you, he'd direct the airliner
away from you before the TCAS system would!

Remember, metal airplanes have their transponder antenna mounted on the
bottom of the airplane, yet they are able to trigger a TCAS system. I
believe the important factor is the airliner is relatively close to you,
so it receives the transponder signal regardless of the antenna
location. The ground station is much farther away, and that is when a
bottom antenna location will work better.


Has anyone actually measured the antenna patterns for top or bottom
mounted transponder antennas on a typical carbon glider? Is the
masking a real problem?

I haven't heard of any, but Tom Knauff once reported his Duo Discus had
the antenna mounted behind the canopy, and performance seemed adequate.


--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA