Hardware Hacking Projects for Geeks

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Part II: Advanced Hacks, Tools, and Techniques

Project Demo

Have a friend carry the transmitter package a few blocks from the receiver

system. Make sure both systems are switched on and working on the same

radio channel. You should soon see an image like Figure 12-14 on your own

APRS screen.

The PDA- or laptop-based receiver can track many location transmitters as

long as each has a unique identifier. Once you get one or two working, you

may want to extend the range of the system. Read the Extensions section

below for some pointers.

Each location transmitter works on a specific frequency or channel, so be

sure to set the radios to the same before operation. The software running

on the receiver allows you to record and save the received location data for

later analysis and enjoyment. Experiment with the settings of the software

to see what they do.

The trackers can be a lot of fun in a city, on a road trip, or when hiking in

the woods. They can be used to watch the location of runners, bike racers,

or the family car. (Just make sure that you tell the person using the car that

its location is being watched!)

Extensions

The two-way radio is limited in output power to 500 milliwatts. If you’re

using well-made radios and operating them in an open environment, you

should be able to get several miles of range. If you want a little more range,

there are a number of things you can do.

Use a GMRS radio

General Mobile Radio Service (GMRS) radios have a higher power output

than two-way radios and are also a little more expensive. Note that if you

buy one, you are legally obliged to fill out a simple FCC operating applica-

tion. There is no test to pass—you just need to fill out the paperwork.

Modify the antenna in your two-way radios

According to the FCC, you are not supposed to modify the antenna on your

two-way radio, so what I write here is for information purposes only.

Open up your two-way radio case and locate the antenna and its connec-

tion point on the circuit board. Also locate the nearest ground point on the

circuit board by using a multi-meter to measure resistance. With one probe

touching the minus battery terminal, use the other probe to locate a point

with zero or close to zero resistance.

Figure 12-14:

Position reception software

Project Demo

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