User's Guide

Teletrac, Inc. - Prism TM Information and Installation Guide
30 1622-0300 B1 3/18/04
Prism
GPS Antenna
GPRS Antenna
SMB
Red - Batt (+) 12 VDC
Green/Blue - Led 2
Red/White - Led 1
Yellow - Relay 2
Blue - Relay 1
Black - Ground (-)
Orange - High 1 IN
Gray - High 2 IN
White - Ignition
Black - RS232 Ground
Yellow - RS232 RX
White - RS232 TX
Black - Main Ground
Red - Main 12 VDC (+)
Orange/Black - Low 1 IN
Gray/Black - Low 2 IN
SMA
Figure 2 PRISM TM Wiring Scheme
NOTE: To insure that the GPS receiver and power management functions operate properly, it is
essential that the Power input be connected to a constant (unswitched) +12 VDC supply and the
Ignition input be connected to the vehicle ignition or another appropriate key operated line, such
as ACCESSORY that goes low during engine cranking.
ANTENNA PLACEMENT
Available Antennas
NAME VLU
plus
PRISM PRISM TM
Black 3db Whip X X X
White Combo X X X
Hidden Combo – ARC (see note
below)
X X X
Glass Mount Combo X
NO NO
GPS Antenna
Now that there are two antennas and one is a GPS antenna, placement becomes critical. The
received signal levels for the GPS antenna from the satellites are very low in power
(approximately -136 dBm) so that any blockage of the antenna can affect the quality of the
location computed by the receiver. The following figures show examples of good and poor vehicle
GPS antenna mounting locations.
When installing the GPS antenna on a vehicle roof, make sure there are no obstructions close to
the antenna that might block the view 360° to the horizon. Nothing should block the antenna 5°
above the horizon - for example, air horns or marker lights. The best location is usually near the
center of the roof, although it is also desirable to locate the cellular antenna as far from the GPS
antenna as is practical. It is best to keep the antenna at least 12” from any other antenna. IF
using the hidden combo antenna, it should be placed on the highest part of the dash or inside the
headliner, see the note below. Be sure to use the correct antenna for this application.