© 2006 Jackson-Labs
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FireFox Synthesizer User Manual
memory, and the mode will not have to be invoked again unless the unit is turned off for longer than
2 days (typically) or the units’ antenna is moved more than 30 feet.
3.5.6 What is the T-RAIM mode in the GPS receiver?
The FireFox GPS receiver includes an optional Motorola Time RAIM (Time-Receiver Autonomous
Integrity Monitoring) algorithm for checking the timing solution integrity. This mode is invoked via
the front-panel menu, and allows the GPS receiver to check the quality of a satellite receivers’ signal.
It will mask off signals from Satellites that indicate any fault conditions, or if the particular GPS
signal is outside certain limits compared to three or more other satellite signals. This Algorithm
prevents faulty satellites, or adverse atmospheric conditions from affecting the precision of the
FireFox synthesizer. T-RAIM is unique to the FireFox system and its’ Motorola GPS timing receiver.
3.5.7 Why did you not use a cheap, standard GPS receiver?
Competitive products use standard GPS receivers to save cost, or because they were designed prior
to GPS timing receivers becoming available. These receivers are optimized for navigational
purposes, and do not include the benefits of position-hold mode and T-RAIM (see above). Their
tracking filters need to be very wide to allow for speed and directional changes, translating into much
larger inaccuracies in the timing reference output. The timing receiver is typically stationary, and
thus allows for much smaller bandwidth tracking filters, increasing the timing solution accuracy
significantly. Comparable navigational receivers have a typical accuracy of 100ns rms, whereas the
receiver used in the FireFox units has a down to 10ns or better 1-Sigma timing resolution due to its
optimized small bandwidth tracking filters (2ns solutions are possible when using optional sawtooth
correction). The FireFox units further increase the accuracy of the timing solution and the receiver
sensitivity by enclosing the receiver into a shielded metal can to mitigate the effects of temperature
changes and EMI, and by rigorously filtering all power supply voltages prior to entering the timing
receiver.
3.5.8 What types of GPS antennae are supported?
The FireFox system supports both 3.3V and 5V GPS antennae via a standard BNC connector. Jumper
JP4 on the PCB can be set for either 3.3V or 5V output. Many 5V rated antennae will also work with
a 3.3V setting. Jackson Labs recommends mounting any outdoor antennae with proper lightning
precautions.
3.5.9 What do the SAT and STAT items in the LCD display
indicate?
The SAT number indicates the number of satellites that are presently being received and used for the
timing solution. The STAT item is a status indicator, having the following meaning:
BG - Bad Geometry. This indicates that the satellite positions are not differentiated enough to be
usable in Auto-Survey mode.
AQ - Acquiring. This indicates that the unit is looking for satellites to track.
UL - Unlocked. The unit is receiving satellite timing information, but has not finished locking the
OCXO to UTC yet.
Summary of Contents for FireFox
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