User's Manual

DRAFT TrimTrac Locator Technical Manual 26
parameters. Typical RTC Wakeups are in the range of 12 to 24 hours expressed
in seconds.
FIX State
The TrimTrac locator enters the FIX state from either the:
1. IDLE state; OR
2. TRANSMIT state.
Upon entering the FIX state, the TrimTrac locator will:
1. Power up the GPS hardware;
2. Start the GPS countdown timer, T2;
3. Attempt to compute new position fix before the GPS countdown timer,
T2, expires.
4. Collect date almanac and ephemeris data if and only if the
Almanac/Ephemeris countdown timer, T6, has expired (typically every
few days).
The TrimTrac locator will transition from the FIX state to the STATUS state
whenever either of the following occurs:
1. A new position fix is achieved; or
2. The GPS Timeout countdown timer, T2, expires.
Upon transition from the FIX state, the TrimTrac locator will:
1. Reset the RTC Wakeup countdown timer, T1; and
2. Power down the GPS hardware.
The TrimTrac locator will initially attempt a position fix using standard signal
strength sensitivity settings; however, it will automatically switch to enhanced
sensitivity settings if it is unable to acquire a sufficient number of satellites to
compute at least a 2-D position.
In practice, it is best to position the TrimTrac locator with as clear of a view of the
sky as possible even though it has the ability to automatically switch to enhanced
sensitivity. In so doing, the average time to compute position fixes will be
reduced (38 second versus 400 second warm starts for –130 dBm and –136 dBm
signal strengths, respectively) while realizing commensurate reductions in power
consumption and improvements in battery-life.
STATUS State
The TrimTrac locator enters the STATUS state from either the: