Locating Transponder Antenna on top of the fuselage instead of under it.

5Z wrote on 12/29/2019 10:11 AM:
On Friday, December 27, 2019 at 5:22:04 PM UTC-8, wrote:
I put mine on a turtle deck on my ASW 27 and it works fine no issues with anyone seeing me or even worrying about it I really like the fact that it's there and was really easy to install compared to down by the gear

Long ago someone (I believe from Arizona) posted here about doing some research by talking to folks very familiar with FAA radar design about putting the transponder antenna on top of the fuselage. The conclusion was that if very near and above the radar site, the signal *might* be blocked. Other than that, it should be fine. Since we do a lot of turning, the antennal will be blocked for times anyway.

One reason for a transponder is to be seen by large aircraft TCAS, it's more likely they will be descending on a collision course, so having the antenna on top is a better idea....

Near airports, airliners are descending and ascending; in between they are above
18K. In our area, the C-17s cruise high and low; the low ones (2000' agl) are
never a problem, but the other ones do cross our normal altitudes at least twice
each flight. I'm skeptical that they are mostly descending, but I think their TCAS
can easily detect us when they get within a few miles, regardless of the
top/bottom location.


--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1