Users Manual Part 1

NTS_Free_Run_Timer the operator is informed by the GPS AND NTS LOST alarm that the NTS is
failing.
4.8.2
Tracking Criteria
To allow a system to successfully initialize for the first time at a new location, the Position Dilution Of
Position (PDOP) must be less than 2.0. A low PDOP value indicates a low error (higher accuracy) in
the position calculated by the GPS receiver. A site with a large PDOP value may incur a delay when
the site is first initialized.
PDOP is an accuracy factor, which is a function of the relative positions of the satellites. If the satellites
being tracked by the GPS receiver are within close relative proximity to each other, the resulting PDOP
is poor. Conversely, if the satellites are relatively far from each other, PDOP improves. Because any
error in position results in a timing error in the BR transmission, the BRs are not allowed to key until the
position error is acceptably low.
CAUTION: After FRU replacement or moving the Site Controller in some other manner, the
position memory is reset using MMI commands.
Excessive PDOP values may result from the GPS receiver not having an adequate view of the sky to
initially determine its position. Motorola Solutions recommends locating the antennas such that there
are no PDOP values that exceed 10.0 for periods of more than 15 minutes. Maintaining a maximum
reliability requires tracking four satellites at all time.
Site Reference requirements for proper operation:
• Tracking a minimum of four satellites during initial start-up
• Sustaining PDOP less than 10
• Working in 3D fix mode for the most of the time
4.8.3
GPS Start Up
GPS startup is the significant contributing factor in determining system start up times. The start up
times are counted from applying power to the system until GPS LED is solid green illuminating.
Initial Start
This is the first time an MTS is powered on or after the almanac or position information has been
erased from non-volatile memory (NVM). The site needs to locate 4 satellites and then train the
reference oscillator from an unknown state.
Warm Start
The MTS has been previously powered up and the non-volatile memory contains valid almanac and
position information and the reference oscillator was trained before starting the site. The times quoted
are for a power-off restart. A software restart will be slightly faster.
6802800U74-AP
Chapter
4: Hardware Installation
137