Symmetricom XL-GPS User Manual

1

Following initialization, the front panel display of an XL-GPS with only one GPS receiver (GPS Status: 
Unlocked) would show the following:

UNLOCKED

* GPS PRI

LOCAL

365:16:01:05 1969

With the GPS receiver as a valid time reference, the following changes would take place: 

•

The asterisk (“*”) indicating the absence of a valid reference would disappear

•

The system status would change to locked

The front panel status display would look like this:

LOCKED

 GPS PRI

LOCAL

233:18:21:29 2005

Once the GPS receiver is a valid time reference, it requires at least one “good current” satellite to remain 
a valid time reference. If “good current” GPS satellites become temporarily unavailable, GPS status 
changes to unlocked and the XL-GPS stops using the receiver as a valid time reference.

Typically, when a “good current” satellite becomes available again, GPS status locks and the receiver 
becomes a valid time reference almost immediately. Typically, the receiver it does not need extra time to 
resolve its current position unless it is being used in a very mobile/dynamic environment such as an 
aircraft. 

If the unit is powered-cycled, the receiver repeats the complete position and leap-second acquisition 
process before GPS status locks.

GPS satellite visibility and signal strength affect the ability of the GPS receiver to lock and provide 

valid time to the XL-GPS. Therefore, it is very important to select the best possible antenna site 
and follow the recommendations in sections 

, and. 

The GPS antenna is powered by a 12-volt current from the ANTENNA connector on the rear of the XL-
GPS. If this circuit is complete (e.g., connected to an antenna) GPS Antenna status is OK. If the circuit is 
incomplete (e.g., no antenna, a cable break, or a splitter) the GPS Antenna status is Open. If circuit 
detects a short, the receiver opens a relay to disconnect power from the circuit, and the GPS Antenna 
status is Open.

In Time Mode: The system has been instructed by the user that its position will remain in a static location 
and has set the GPS mode to Time Mode. 

•

Start Site Survey: The receiver is checking for changes in its saved static position (occurs after 

boot). 

•

Survey Position: If the save static position is determined to be invalid, the receiver begins to