Data Hacking

Antenna Hacks
Making the most out of your GPS depends on getting a good signal
from the satellites, which orbit the Earth at an altitude of around
20,000 kilometers (12,000 miles). This signal isn’t a strong one;
it’s roughly equivalent to detecting the light from a 25-watt lightbulb from
16,000 kilometers (10,000 miles) away.
In other words, without a good signal from the satellites (at least three of
them, preferably more), you aren’t going to be able to use GPS at all, or the
information it gives you will be erroneous. You can solve this problem by
adding an external antenna to your GPS unit.
This chapter examines the GPS antenna and how you can maximize a weak
signal when you are on the move.
The GPS Antenna
One part that all GPS receivers have in common is the antenna, whose
job is to receive the signal from the satellites and pass that signal on for
processing.
The signal the antenna picks up is a UHF signal with a frequency of
1575.2 MHz (this is the civilian, unencrypted frequency; the military signal
uses 1227.6 MHz). This frequency offers all-weather navigation capability,
but is blocked by walls, ceilings, and even trees.
GPS receivers usually come with one of the following antenna types
attached:
Quad-helix
Patch
Receivers such as the Garmin III (shown in Figure 4-1), and most
Magellan units, make use of the quad-helix style antenna, while units
such as the Garmin eTrex (see Figure 4-2) use the patch antenna.
chapter
in this chapter
˛ The GPS antenna
˛ The helix antenna
˛ The patch antenna
˛ Antenna extras
˛ Signal losses
˛ Repeating antennas
˛ Building your own
antenna