Probably the simplest approach (since the antennas are
fixed to the radios) is to use body shielding: hold
the radio right up against your chest and turn around -
when the transmitter is behind you, your body will
block the signal and the received signal strength will
drop. (This is a great way to have a transmitter hunt
using 2m HTs, since almost everyone has one. It is
also quite entertaining to watch the pirouettes!)
One problem with this approach is that the signal will
often be too strong to hear the null - this limits how
close you can get to the transmitter and still get a
good bearing. A quick solution is to make a cardboard
tube large enough for the radio to slip inside, and
cover it with aluminum foil. Something about a foot
or more in length should work, longer may be better up
to a point, especially since you can't take the antennas
off the radios.
Tie a string on the radio and lower it into the tube
until the received signal gets noisy. Then repeat the
body shielding trick: with the radio the right depth
in the tube, the null should be quite distinct. (On
an unmodulated carrier, the back ground noise will be
easier to detect that the complete lack of signal.)
If you wanted to make a beam, the easiest approach would
be to use a reflector, either a flat plate or a corner
reflector with the radio mounted directly at the feedpoint.
An old metal trash can lid with a handle might be ideal
if you could still find one around somewhere. W4RNL
has some good info on optimum reflector sizes (for
example,
http://www.cebik.com/pcr.pdf) but something
about 2' square would be a good start. Fortunately
the exact dimensions for the reflector aren't too
critical, and it can be made from hardware cloth, sheet
metal, an old BBQ grill, or cardboard covered with foil.
The problem with the beam is how to detect the strongest
signal, since the FM demodulator is designed to remove
all amplitude differences from the output. This is
why I think hunting the null (where the signal drops
into the noise) is more practical with these radios.
Perhaps we should have a separate thread for discussing
the use of DF with Scout and other groups, separate
from the technical discussions? One local Scout group
here is using 80m DF receivers and having a great time!