Transponder location inside Kitfox

[LetMeFly]

Hi all,
I decided to mount my transponder and ADS-B antennas inside my Kitfox 7SS. I'm trying to prevent them from getting snapped off if they protrude from the bottom. I built a ground plane mount to attach to the steel tube fuselage, but Id like to get some input from you out there, including Dynon techs.

See the included pictures. I know the angle posts will block some of the signal to those quadrants, but do you think it will be significant? Would changing to aluminum rods or wood dowels make a big difference? FYI the antenna is ~1 1/8" away from the fuse. tube cross member. Thanks for any input.

 

[Rhino]

If you're going to mount it inside, I would first try mounting it in the top instead of the bottom of the fuselage. The tubes shouldn't present much of a problem, if any. But the ground plane might, because it could possibly block signals below that ground plane (above if it's mounted upside down). Vertically polarized antennas transmit primarily to the sides, and the signal lessens at higher angles. They don't transmit very well at angles lower than the ground plane itself. They even weaken a bit when getting close the ground plane level. It looks something like this:

That diagram depicts no signal below 90 degrees (the ground plane), but that assumes ground is Earth. In an airplane, you will get signal below 90 degrees, but it will lessen quite a bit. I'm not saying it won't work. It might work fine, especially when you consider that receivers or transmitters below are going to be closer, so you don't need as much transmitted power to get through. Some aircraft have their ADS-B antennas on top, and they seem to work fine, at least as far as I know. If it were me, I'd start with a temporary mount, and experiment with different locations. Then make it permanent when you find the best one. I also might consider using 1/4 wavelength radials instead of a solid plate, because that won't block as much signal below the ground plane. Be sure to use good quality antenna cable, RG-400 or better. Too many builders skimp on cable, and end up regretting it later.

 

[SkippyDiesel]

You are overcomplicating the problem & the solution.

Your concern about the transponder antenna being snapped off, would be better addressed by fitting a flexible antenna.

You can make your own flexible antenna for just a few dollars.

All that is required is a the base, purchase from any half descent electronics store or aviation parts supplier.
Short length of multi core wire.
Solder.
Shrink tube.

Solder wire to base. Cut wire to exactly same length as antenna shown. Cover using shrink tube. You now have an almost indestructible antenna.

 

[LetMeFly]

Yup! I was trying to get fancy. I've gone to the transponder and ADS-B IN antennas installed out the bottom.

Thanks for the feedback!