Airborne DF

Doppler sometimes does not work well if there are reflections - but the
aircraft has an advantage over ground vehicles so it could have a better
success rate. Because the signal is line of sight, you can reduce the
length of the antenna and still have an adequate signal, although you will
have a reduced range. Rubber ducks can be used, although flexing can affect
directivity.

Another option is to install a number of directional antennas and switch
between them. The aircraft has an advantage in that it can be rotated
fairly easily. With a good signal indicator, you could home in on the
hunted signal. I have one of the Ramsay Dopplers and normally use it on the
ground for Search and Rescue. We search in rugged terrain and I have not
found it as useful as a directional antenna.

Years ago a friend of mine built a Doppler to use in a hidden transmitter
hunt. Soon after the start, he realized it was not working, but he had left
all of his other direction finding gear at home. He got his handy talkie
with rubber duck out and drove around finding the strongest signal. He
would drive behind buildings to determine directivity - since the building
would make the signal weakest if it was directly in the path. He was first
to arrive at the hidden transmitter, proving that it is the operator rather
than the equipment that is key in direction finding.

Colin