DF Antenna Position

[a2capt]

If you were going to install DF antennas on your aircraft ..

.. would you want them on the top or bottom?

Shadowing can certainly be 'easier' with them top mounted. With the signal nearby below it's really hard to shadow it otherwise.

CAP aircraft tend to have antennas in both places for whatever factor was the reason during installation.

[JoeTomasone]

There's arguments for both:

On top: Shadowing, as you mentioned, and for ramp checks when landed, possibly.

On bottom: Range while airborne.

[CadetProgramGuy]

You can still wing null with antenna on the bottom of the aircraft.

It takes 45 degree turns thogho do it.

And a VERY strong anti-motion sickness MS in the back.

[Gunner C]

My former unit had a C-182RG with antennas on top.  Personally, I prefered them set up that way - I could overfly an ELT and locate it with a few feet.  I never had an issue with range. 

GC

[wingnut55]

trying to DF a signal through the metal of an Aircraft makes no technical sense, I doubt if that was an approved install by the MFG. Antenna placement is critical with any receiver or transmitter. With the Global Star transceiver it is highly critical, but like many things in CAP the important technical information gets lost in the noise of proper flight suits, summer BDUs, ribbon placement  etc.

[desertengineer1]

If you were going to install DF antennas on your aircraft ..

.. would you want them on the top or bottom?

Shadowing can certainly be 'easier' with them top mounted. With the signal nearby below it's really hard to shadow it otherwise.

CAP aircraft tend to have antennas in both places for whatever factor was the reason during installation.

I would think the bottom is preferred.  You want the far field antenna pattern to be as isotropic and smooth as possible - i.e. smooth and round with minimal disturbances - with respect to the surface.  High mounted antennas work well for airborne and long distance, but suffer with respect to the downlook pattern.

Yes, the argument can be made that as long as the patterns are "mirror image", directional differentiation is preserved, but the pattern will fluctuate more at closer range.