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Transponder antenna location

 
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jszantho(at)gmail.com
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PostPosted: Tue Oct 27, 2009 12:34 pm    Post subject: Transponder antenna location Reply with quote

I plan to position my transponder antenna (GTX330) just behind the firewall on the left, next to the fuel vent line (RV9A). This location is about 34” from the back of the transponder. Do you guys see any problems with this location, if you do where would you place the antenna. The whip-style COM antenna will be located behind the pilots seat. Also do you know of a good wiring diagram between the SL30 and the GMA340 audio box. Thanks for any help.
John
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sarg314(at)gmail.com
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PostPosted: Tue Oct 27, 2009 2:46 pm    Post subject: Transponder antenna location Reply with quote

John:
As a rule of thumb an antenna wants a ground plane around it that is infinite.  In practice it should be at least (roughly)  a wave long or so in all directions. The more the better.  What I mean is that the antenna might have a more radially uniform pattern if it was not right at the edge of the floor skin, immediately behind the firewall. That gives it an asymmetric ground plane and will distort the antenna pattern.  I put mine closer to the gear weldment (on a 6A) so that it was under the seat skins. I kept it about 1 wavelength away from the steel (=conductive) landing gear. (at 1GHz 1 wave is about a foot - your xponder antenna is 1/4 wave).

I haven't run the thing yet, so I can't tell you that it works well there, just that it should work better there than at the forward edge of things.  In practice it might not matter much.  Still, I thought it better not to tempt fate.  Antenna design is a black art. 

On Tue, Oct 27, 2009 at 1:33 PM, John B Szantho <jszantho(at)gmail.com (jszantho(at)gmail.com)> wrote:
Quote:

I plan to position my transponder antenna (GTX330) just behind the firewall on the left, next to the fuel vent line (RV9A). This location is about 34” from the back of the transponder. Do you guys see any problems with this location, if you do where would you place the antenna. The whip-style COM antenna will be located behind the pilots seat. Also do you know of a good wiring diagram between the SL30 and the GMA340 audio box. Thanks for any help.
John
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