Transponder aerial

juliant · Post by **juliant** » Sun Sep 28, 2008 3:46 pm

Hi
What is the best place to mount the transponder aerial? and what sort of ground plane is required . Anyone got any pics?
thanks
Julian
NZ

gme9261236 · Post by **gme9261236** » Sun Sep 28, 2008 4:06 pm

I do not have a pic but mine is mounted just under and slightly behind the pax seat (but still forward of the rear cargo). It has a 10" piece of stainless steel for a base and is mounted facing down with the stainless on the inside of the plane. Works great with no problems.

b1x4nqb · Post by **b1x4nqb** » Sun Sep 28, 2008 6:54 pm

Do a search on "antenna mounting" and you will find some good info from Wes. Here is the link, if it works.

Paul, PA

http://www.wingsforum.com/viewtopic.php ... ht=antenna

gme9261236 · Post by **gme9261236** » Sun Sep 28, 2008 10:56 pm

I forgot to mention WES. He is absolutely the go to avionics guy on this site.

juliant · Post by **juliant** » Mon Sep 29, 2008 3:33 pm

Thanks link works fine.
Useful stuff.
Julian
NZ

jak · Post by **jak** » Sat Oct 04, 2008 1:18 pm

Julian I've been trying to post a reply to you for threee days and my piece of crap computer hasn't let me. Anyway here at the factory we put the transponder ant. on the plate that covers the opening at the rear on the bottom of the fuse. That way no additional metal has to be put into the bottom of the plane. Jak

b1x4nqb · Post by **b1x4nqb** » Sat Oct 04, 2008 1:29 pm

I know little about this stuff but I thought you wanted the antenna and actual transponder as close to each other as possible. Does that have any effect on the signal strength with a loss due to the longer length?

Paul, PA

jak · Post by **jak** » Sun Oct 05, 2008 8:22 pm

There has to be at least 9 ft of cable for the numbers to work when we hook it up to do the certification. It dosn't hurt for it to be longer. Jak

Wes · Post by **Wes** » Sun Oct 05, 2008 10:38 pm

Wooohhh, wait a minute guys, are we talking about transponder antennas?
Transponders operate around 1 GHZ and the signal attenuation in coax at this freq is terrible. Some coaxes are better than others, but readily available coax types that are over 6 ft in length will attenuate the TX and Rcv signals well in excess of manufacturer reccomended specs. (1.5 db max. for the Garmin 327).
So again, in my opinion you are severely compromising your ATC transponder system if you run long, lossy coax to the tail mounted antenna. Will it 'work' ?, well maybe, - will it work on the edge of the radar coverage area, where you really might like to have it ? - probably not!
In this case, longer is definitely not better!

'Just' my opinion.

Wes

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