Thanks Ed. That's a good idea, and you're exactly right... what we're
doing looks just like what you'd see on a television nature show where
someone had a radio collar on a lion or something like that. We're
applying the same technology to Alzheimer's patients who are at risk
of wandering.





You're welcome. You might also consider some of the new GPS
products.... often made for tracking cars... but some small enough to place
on a person. You could sit at the comfort of a computer and track them!

Ed :^)

On Thu, 20 Mar 2008 05:44:50 GMT, "usmcbrat"
wrote:

Hi Folks:

I'm looking to make a directional antenna in the 215 to 218 MHz band (215 if
that's too broad), used for location of dementia patients who have wandered
away from their caregivers. I'm a volunteer with an organization that
locates these people. They wear a tiny transmitter which emits a chirp that
can be heard from 1-2 miles on the ground and 8-10 miles via helicopter.

I'm somewhat new to the program, and I'd like to do some investigation on my
own regarding antenna types that would be useful, and I hope you'll all
grant me a few questions.

My needs are this.... the antenna must be as directional as possible. It
must be most efficient in the 215 to 218 MHz band 215 is what our patients
are on right now, though after we fill up that range we have licensed
through 218 MHz. It must be easy for an individual to carry, and portable
enough to carry through any type of terrain. It must be shaped in such a
way that it's relatively safe and easy to use in an enclosed area, either in
a helicopter or a car. Currently the agency is using a 4 element Yagi,
which works well, but has the drawback of being a real eye-poker when used
in close quarters, and in fact the California Highway Patrol will not allow
them to be used in their helicopters because of that reason.

One of our Search & Rescue guys built his own 4 element Quad Yagi out of
some 1/2" PVC pipe and other parts that are readily available at any Home
Depot. It has greater sensitivity than our stock antenna, and the CHP has
said that it's OK to use in their helicopters. Rather than 4 horizontal
straight beams it has 4 squarish beams, with no points to poke people's eyes
out. I'm still waiting to get the plans from him for that antenna, and I
though that in the meantime I'd ask in here if any of you had some
interesting leads for me to follow.

Many thanks!

I just did a quick simulation on EZNEC of your proposed Quad. At 215
mhz the element spacing on the boom is about 1 foot. That means a 4
element yagi or quad should come out to 3 feet long. Similarly, the
element loops will be about 1 foot square.

With no matching attempted 2:1 Swr is easily achieved.

If you are so inclined you could model this antenna with the Demo
version of EZNEC. You could also prototype one or more on the kitchen
table with masking tape and sticks!

I would think the additional gain of the Quad would make it desirable
to drop back to three elements to reduce the size.

John Ferrell W8CCW
Beware of the dopeler effect (pronounced dope-ler).
That's where bad ideas seem good if they come at you
fast enough.

"Ed_G" wrote in message
You're welcome. You might also consider some of the new GPS
products.... often made for tracking cars... but some small enough to
place
on a person. You could sit at the comfort of a computer and track them!

GPS was discussed in our training, with the main drawback being that if the
patient was in a building or under a canopy of trees, etc, there would be no
signal.

"John Ferrell" wrote in message
I just did a quick simulation on EZNEC of your proposed Quad. At 215
mhz the element spacing on the boom is about 1 foot. That means a 4
element yagi or quad should come out to 3 feet long. Similarly, the
element loops will be about 1 foot square.

That sounds *exactly* like the one that we used in our training. The guy
who made it said that he used an antenna design calculator on the internet
to come up with the layout. I'm still awaiting plans from him, and in the
meantime I'm interested in seeing if I can do it myself for the technical
exercise.

If you are so inclined you could model this antenna with the Demo
version of EZNEC. You could also prototype one or more on the kitchen
table with masking tape and sticks!

I'm going to take a look at EZNEC and also google around for "Cubical Quad"
as suggested upthread by John KD5YI. So far this looks like exactly what
I'm looking for.

Thanks!

On Mon, 24 Mar 2008 03:28:19 GMT, "usmcbrat"
wrote:

"John Ferrell" wrote in message
I just did a quick simulation on EZNEC of your proposed Quad. At 215
mhz the element spacing on the boom is about 1 foot. That means a 4
element yagi or quad should come out to 3 feet long. Similarly, the
element loops will be about 1 foot square.

That sounds *exactly* like the one that we used in our training. The guy
who made it said that he used an antenna design calculator on the internet
to come up with the layout. I'm still awaiting plans from him, and in the
meantime I'm interested in seeing if I can do it myself for the technical
exercise.

Again, I would suggest a search of the Google archives in research of
the term "Foxhunting." Antennas with such gain may appear the obvious
choice by graphics of their radiation characteristics, but there are
more matters to location than putting a signal in the peak of a lobe.

I have a friend who has lead many Search and Rescue operation in the
city looking for patients who have "wandered away." Quite frequently
they passed by their quarry (quite closely) simply because of the
urban clutter that presents antennas with these characteristics very
confusing results.

On the other hand, and as many sailors may attest, sharp nulls are
often more compelling location indicators. Such an antenna as the
W8JK with variable phasing can give you both sharp nulls and general
gain (through careful selection of the drive point) on a shorter boom
(and could be designed in the way of a quad).

73's
Richard Clark, KB7QHC

"usmcbrat" wrote in message
news:5_cFj.257$rb6.143@trnddc01...
..I'll be persistent and let people here
know when I get the plans.

I still don't have "plans", but here's a picture. Turns out it was a 3
element. My apologies for such an inaccurate memory.

http://img168.imageshack.us/img168/5...ining1shk5.jpg

"usmcbrat" wrote in message
news:01HGj.3370$rb6.1690@trnddc01...

"usmcbrat" wrote in message
news:5_cFj.257$rb6.143@trnddc01...
..I'll be persistent and let people here
know when I get the plans.

I still don't have "plans", but here's a picture. Turns out it was a 3
element. My apologies for such an inaccurate memory.

http://img168.imageshack.us/img168/5...ining1shk5.jpg


Hi "UMC"
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.

Jerry KD6JDJ

I still don't have "plans", but here's a picture. *Turns out it was a 3
element. *My apologies for such an inaccurate memory.

How about a small Yagi made with "rubber duckies"?

Mark

"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

"Mark" wrote in message
...

How about a small Yagi made with "rubber duckies"?

I admit it, I don't know what you mean.