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fwd trandponder ant mount ????

HIIFLY

Well Known Member
Has anyone mountea a transponder antenna just behind the fire wall on the doubble floor belly in frt of the landing gear leg on an RV-8 . ??
Or on the wing inspection panel about the middle of the wing ?? Any opinions would greatly appreciated . I'm ready to drill .
 
I'm certainly no expert on this, but I'd think that both locations would be a problem due to distance from the transponder itself. Too close in the case of the forward location and too far away in the case of the wing mount. The transponders I know about want the antenna at least six feet away from the transponder. Because of the frequencies used by the transponder, you don't want the antenna too far away because of power loss. More knowledgeable people will chime in, I'm sure.
 
The antenna should be 3 feet from the transponder itself, recommended max cable length for RG400 is 8 feet (this is from the GTX327 manual).
 
Ant. placement

Thanks for your input. I have read as many articles as I can find and know thr 3' and 8' coax and 36" distances required from the comm ant. . I have mounted my two comm ant on the belly aft of the spat 8" so when I measure 8' rear of the bent whip "TIP" it measures 8"8" just a little beyond the 8' max coax lenght allowed . Now if I come out the wing root behind the push/pull tube I can get 4' from the comm and stay with in the 8' max coax lenth . But I have never seen an airplane with the transpondre antenna on the bottom of the wing . Has anyone seen this set up ? And going forward on the belly is only 2' or so . That's out.
 
I would like to hear more on where people are mounting the transponder and comm antennas on the -8. To maintain the 3 ft. min seperation distance between the the comm antenna and transponder antenna, one or the other would have to be back near the aft battery location. The width of the fuselage is less than 2 1/2 feet. So putting one on one side and the other on the other side would not work if you kept the distance. Thanks Lyle
 
Antenna Locations

I found that every antenna location was a compromise...I looked at lots of examples and Osh and mounted mine.

Two comm antennae are just behind the spar box under the pilot's seat. Outboard as far as possible, with joggled doubler plates tying in to the spar and outboard rib flanges. Not 3' apart, but as wide as they can be and still be in the fuselage.

The transponder antenna is aft of the rear spar, slight forward of the battery box area and outboard of the battery/baggage floor rib.

Best,
Mike
 
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