Lately I've been thinking it would be cool to put a GPS transmitter
into a rocket for tracking purposes. I've found some really
lightweight and small GPS recievers out there, but I have not yet found
an inexpensive data transmission means. It seems that a quick and
dirty way to do this would be to hook up the RS-232 output of a GPS to
a data radio modem and then downlink the signal with another similar
unit on my computer. I do no thave my HAM lisence (yet), so that
limits some other avenues. Does anyone have any experience with this
or any good ideas? Thanks!
You can use commercially available RF modules, for example
(www.lemosint.com). The lower power ones (~1mw output) do not
explicity require a license as long you meet part15 guidelines. The
problem with these is that at this low power level you are probably
going to lose signal when the rocket lands at an appreciable distance
(kind of defeats the purpose of GPS). However you should be able to get
good signals during descent with a good directional antenna which will
get you in the neighborhood, then you should be able to get a good
My students http://www.spacewifi.com/ used a credit card sized Linux
computer, GPS receiver, and a CompactFlash WiFi card.
http://www.bigredbee.com/BeeLine.htm is working on transferring serial data.
Doug says that Ivan is working on putting a GPS receiver into their
http://www.byonics.com/pockettracker/ looks interesting. More info
about amateur radio and APRS tracking is at http://www.aprs.net/ and
many other places on the web.
Ramsey Electronics had/has a "Model Rocket Tracking Transmitter Kit"
http://www.ramseyelectronics.com/downloads/manuals/MR6.pdf that will
take an audio frequency telemetry source and modulate it. The MR6 isn't
listed in their online catalog but I was able to call and order one as
of a couple of months ago. They have kit and pre-built versions. I
don't recall the exact price but the kit was around $30 or $40.
For a DIY method, it'd probably only take a single chip to
convert the rs232 signal to FSK audio frequencies that you could
feed into a low power 500mw CB radio walkie talkie.
On the ground, you could either run in into another chip to restore
the digital data before running it into your laptop (if you want to
view it with your own software), or even get the audio data fed into
a soundcard with suitable software to do the decoding (if all you
wanted was to view the data).
Its probably not the ideal solution, but cheap and possibly fun
to experiment with. Maybe ask for more ideas in the amateur
radio newsgroups. Some of those guys do a lot of this kind of
If you're only looking to transmit location, consider APRS (automatic
position reporting system). The basics are that a GPS outputs location
through an intermediate device to a transmitter, which sends it via
packet radio to your computer. All you really need to transmit is a
GPS, a small 2m or 70cm transmitter (cheap on ebay), and something like
I haven't used tinytrak, but people say it's really easy to use. It
also is pretty inexpensive (your GPS unit alone would cost more than a
cheap handheld transmitter and the tinytrack combined).
To receive the signal, all you need is a receiver (like a police
scanner that picks up the frequency your xmitter transmits) and a
computer with a sound card or terminal node controller (TNC). There's
other things you can substitute for the computer, soundcard/TNC, and
tinytrak, but the concept is the same.
Assuming you already have a GPS unit and a computer with a sound card
(or a terminal node controller), the transmitter, scanner, and tinytrak
combined will probably run you about $130 if you get the xmitter and
Another option (if you can program microcontrollers, like the Basic
Stamp) is to output the GPS data to a microcontroller, which creates an
audio signal that's jacked into your transmitter. You can output Morse
Code (CW), RTTY, AMTOR, or whatever floats your boat. There's freeware
you can download that will decode it real time on your computer. This
method also gives you the ability to transmit more than just GPS info
(pressure, temperature, etc).
Hope that helps,
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