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.


You might do a bit of research on the equipment that various animal
tracking organizations use. They tend to use the 215 - 218 MHz band for
tracking various animal species, and the equipment should suit your needs
also.


Ed K7AAT

"Ed_G" wrote in message
You might do a bit of research on the equipment that various animal
tracking organizations use. They tend to use the 215 - 218 MHz band for
tracking various animal species, and the equipment should suit your needs
also.

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.

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 :^)

"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.

On Thu, 20 Mar 2008 23:52:07 -0400, wrote:

Do a search for "tape measure antenna". It is a simple to build yagi
antenna made of pvc pipe with elements made from a metal measuring
tape. You can rescale it to your frequency.

Kingfish

Rumor has it that this antenna will be in the next ARRL Antenna
Handbook. Our club had an antenna party here recently where we built a
bunch of these. I chose to not glue mine together so it will store in
a very small package. You can also leave off elements at will to
reduce the physical size if needed.

Unfortunately, recent knee replacement has left me sidelined for a
while.

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.

wrote in message
...
Do a search for "tape measure antenna". It is a simple to build yagi
antenna made of pvc pipe with elements made from a metal measuring
tape. You can rescale it to your frequency.

Kingfish

Thanks Kingfish. That's pretty cool! It's actually much like what we're
using now... A 4 element Yagi, though ours don't have the flexible elements
like one made of tape measure.

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.

"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