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Old March 28th 08, 01:47 AM posted to rec.radio.amateur.antenna
usmcbrat usmcbrat is offline
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First recorded activity by RadioBanter: Mar 2008
Posts: 12
Default Directional antenna in the 215 to 218 MHz band


"Jerry" wrote in message
news:SeOGj.4383$Dv5.2658@trnddc02...
Is it practical to mount the antenna outside toe helicopter? I once
designed an antenna system for military helicopter VHF homing. I used
two dipoles made of foil taped to the plastic windshield. It worked.
The idea was/is simple, but you'd need to build a seperate electronic
device to go between the antenna and the receiver. And, you'd (of
course) need to manuver the helicopter rather than twist/turn the antenna,
because, the helicopter would be the antenna.


Hi Jerry:

I guess if the helicopter was specifically part of the searching agency then
you could do something like that. I'm not sure if they'd ever do that. The
choppers and pilots are usually "on loan" from whatever agency is available
to help when someone's lost. The CHP has some, most Sheriff's departments,
Feds, Military, State Police, etc. When a person is lost, people seem to
come out of the woodwork with the desire to help. That often includes
agencies that own helicopters.

While I'm now a certified trainer because of my classroom time, I'm still a
brand-newbie to search and rescue, and have never been on a "real" search
for a missing person. I've located hidden transmitters on dozens of
occasions, either hidden on a person who was part of the training, or just
plain hidden. If I can get within a couple of miles of one of the
transmitters I can normally go straight to it, even if it's down a
drainpipe, under a bridge, or behind the coffee maker in a restaurant... it
doesn't really matter much where it is located.

More of our training is related to understanding people with Alzheimer's and
other forms of dementia than is related to actual radio work, and rightfully
so. There's much to study on the human side of it. One of my greatest
fears now is that I'll search for a person who is at a significant danger of
being injured and is lost in a giant crowd of people, and they don't want to
be found. I feel uncomfortable "pointing" the antenna around crowds of
people for obvious social and psychological reasons. An example might be
someone "lost" in Time's Square on New Years Eve.... the very thought
shivers me timbers!

Luckily, being from Central California, I'll be much more likely to be
searching orange groves than giant crowds. Interestingly, orange groves
absorb a signal much more than I had thought they would, and, the signal
propagates much better down the rows than across the rows. The trees were
laden with oranges and I could barely hear a signal from one of our guys who
was purposely trying to avoid us. He was literally 5 or 6 rows in (across)
and I could hardly hear the signal. Once we got to the end of the grove and
got to look down the rows, the signal jumped.

Thanks again for all of your help!

MB