Micro transmitters/receivers for finding objects?

Hello,
I was wondering if you could help me. I would like to do the
following:
Put a small transmitter onto a product for this example lets say a
model hobby rocket that will be launched using a standard hobby rocket
engine you can buy in any store. They usually don't go more than
100-200 yards or so but I would need the device to be able to locate
it in dense tree cover (woods) without being able to see exactly where
it went.
Is there a receiver that can direct me exactly to the spot where the
rocket is? (containing the beeping transmitter).
Of course there are some constraints:
- the size of the transmitter has be very small (approx 4mm wide or
less, it can be several mm's longer in length). Also the battery has
to be this small as well, possible cylindrical in shape.
- the receiver that will direct me to the transmitter also has to be a
relatively small device (like the size of a walkie talkie, if
possible)
- each of these units should be somewhat inexpensive to produce (under
$20?)
- no FCC or other federal licenses required
- relatively easy to learn and accurate if within the 100-200 yard
range

Is this possible? Does anyone know where I can find these components
or companies that can produce them?
If not, are their plans that are available where we can build our own
receiver?

If you have any questions, please contact me.

Michael

 

No single receiver, following a simple telemetry signal such as
you describe, can do this without some effort. Said effort takes the
form of triangulation.

Using a directional antenna and compass, you would take a bearing
on the signal from your launch point, and mark it on a map. You would
then walk or drive a couple of miles in a direction approximately 90
degrees to your first bearing and take another one. Repeat this process
once more, and you will have three lines on your map. Where they all
cross is approximately where the transmitter will be.

If you wanted to get really crazy, you could rig some sort of
miniature GPS receiver in the rocket, and have it send its raw serial
data via another transmitter. This, however, gets into some weight and
cost factors that I'm sure would exceed yours.

The receiver is less of an issue than the antenna. The antennas
used in DF work are, by design, considerably larger than the radio.

You may want to get in touch with whatever ham radio club is local
to your area (listings may be found at www.arrl.org), and ask about
transmitter hunting. You may even want to get your ham license along the
way.

Good luck.

 

Thank you very much for your response. I was doing all kinds of
research but no one seemed to even have a clue as to what I was
looking for. I will see how it goes at the ham radio club.

Thanks again.

 

On 15 Oct 2003 20:49:26 -0700, (Michael) wrote
as underneath my scribble :

I have seen for sale (for under £10 ) a small transmitter in a single
2 wire chip, as far as I recall it transmits at 400+ MHz FM ,3-12 v
and looks like a small tantalum capacitor, all it needs is a battery,
and seems inexpensive. Try Maplin etc search for GT39N, the receiver
is another matter, there was a receiver which was the more expensive
part however the direction finding ?? if it were my problem I would
probably start trial with the Tx chip and a handheld scanner type Rx
and a small yagi type directional array ariel which you can make
yourself or adapt a TV yagi array. The scanner would have to have a
signal strength meter and prefrably a BFO as well, or you could add
modulation to the Tx supply and get an audible signal that way! Range
- battery longevity etc, no idea youd have to experiment. You could
also add a small piezzo buzzer to your rocket to get you the final
location within earshot.
Charlie+

snip

 

[snip]

The ferrite loopstick inside(!) the common AM pocket radio can be used
to get a null of an AM transmitter, and by using triangulation as you
stated, can give the location of the Tx. This antenna is not
"considerably larger" than the radio. I don't know if this could be
applied to VHF stations, but if so, it would work similarly.

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These kinds of transmitters are used by the organizations working with
endangered species of animals. Some are small and light enough to be
strapped onto birds. The receiver is a special one with a directional
Yagi antenna that's a few feet long. The receiver gives the signal
strength, and the hand-held antenna is pointed in the direction of
maximum signal. There is no apparent need to do triangulation, just
approach the transmitter in the direction that the antenna is pointing
and as the signal gets stronger, you're heading right for it. If it
gets weaker, then you're going in the wrong direction.

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###Got a Question about ELECTRONICS? Check HERE First:###
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My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
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