T801-4 Installation and Operation Manual
Operation
31
© Tait Electronics Limited September 2007
2.7
GPS Fix Acquisition Times
The T801-4 is designed to operate with either an internal Trimble Lassen
iQ GPS receiver or an external Dalman 40742 GPS antenna/receiver. Each
receiver has different GPS fix acquisition times when powered up.
When a GPS receiver is powered up without any current navigation data
available in memory, the module must use a specific algorithm to search for
satellites and collect ephemeris and almanac data. This process is known as
a cold start.
The Trimble Lassen iQ module provides the option of using a back-up
battery to keep the module’s RAM alive when the prime power is turned
off. The battery continues to power the real-time clock and allows the GPS
almanac, ephemeris and last position to be retained in memory. When the
prime power is restored, the module will then perform a warm or hot start.
The time to first fix will be substantially reduced when compared to a cold
start. The T801-4 is fitted with the back-up battery as standard.
The typical acquisition times for these two GPS receivers are listed in the
following table.
Trimble Lassen iQ
cold start
two minutes
warm start
(receiver has been powered down
for more than 60 minutes)
less than 45 seconds
hot start
(receiver has been powered down
for less than 60 minutes)
less than 20 seconds
Dalman 40742
cold start
two to eight minutes
