TT8750 Installer Guide
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Installing Antennas
There is one GPS and one GSM antenna to install for the TT8750 device; these antennas cover the
required frequencies for the GPS / GSM portions.
The antennas have a magnetic side and also an adhesive side, so it is possible to affix it in position by
placing it on any surface. The antenna can also be mounted with an adhesive pad (included), tape or
plastic cable ties. It may not be necessary to affix the antenna at all if they are located in areas where
friction will hold them in place without vibrating, rattling or slipping.
Positioning and orientation is critical for the GPS antenna.
About the Antennas
GPS signals are much weaker than GSM signals. For this reason, the GPS antenna used with the
TT8750 is what is known as a directional antenna. It amplifies signals from one direction while
attenuating signals from other directions. The signals that need to be amplified come from the GPS
satellites, which may be located anywhere from straight up to just above the horizon. The rounded top of
the GPS portion of the antenna is the direction in which it amplifies received signals. The flat bottom is
where the magnetic side is located.
It is usually desirable to orient the GPS antenna straight up but there are exceptions. If metal in the
vehicle is blocking one or more directions, it is not useful to amplify signals from that direction. As an
example, if the cab of a truck is all metal with the exception of the front and side windows, it is preferable
to aim the antenna out the window, not straight up at the roof of the cab.
It is useful to understand which materials block signals and which do not. A simple rule of thumb is that
materials that conduct electricity will block signals and materials that do not conduct electricity will not
block signals. The thickness of the material is much less a factor than the conductivity. For instance, a
thin film of aluminum foil will block signals almost completely while a thick human body will only partially
block signals. The reason is that the aluminum is an excellent conductor of electricity while the body is a
poor conductor.
Another grey area is where the conductor is not a continuous plane but a mesh, such as the metal
springs in a vehicle seat. The rule of thumb here is that higher frequencies penetrate smaller mesh.
GPS signals are a fairly high frequency so they will penetrate any conductive mesh with holes greater
than about 6 inches across. This is important for places like a car trunk where the majority of the signal is
entering through the back seat and the rear window of the car and down through the package shelf
behind the back seat. Both the seat itself and the bracing for the package shelf typically contain metal
mesh components. Some, but not all, of the GPS signal will be blocked from the trunk space.
Metals of any kind will block signals, however small metal brackets or fittings above the GPS antenna are
generally not a problem as long as they do not block a large percentage of the direction of signal
reception. The following types of materials, generally found in vehicle construction, do not block signals:
plastic, glass, fabric, vinyl, leather, rubber or styrofoam.
The best location for placing the GPS antenna, in a vehicle is on top of the dashboard, directly below the
center of the front windshield. To improve the esthetics of the installation it is usually preferable to hide
the antenna. Placing it directly under the dashboard, up near the windshield, can accomplish both
excellent signal reception and a hidden installation. Be sure there is no metal between the antenna and
the windshield. In most vehicles there are metal brackets in various locations throughout the bottom and
