Jackson Labs FireFly-1A GPSDO, User Manual, Page: 18 / 44

FireFly-1A User Manual
12 © 2011 Jackson Labs Technologies, Inc.
By default the unit is set to GPS. It may be hard-coded to only use the external 1PPS source by
setting EXT, or it may be auto-switched to the external 1PPS signal if the internal GPS receiver does
not generate 1PPS pulses for longer than 15 seconds if the signal is too week, or there is a GPS
failure. When set to the AUTO setting, the unit will switch back to the internal GPS receiver once
1PPS pulses are generated internally again.
3.5.2 SYNChronization:HOLDover:DURation?
This query returns the duration of the present or most recent period of operation in the holdover and
holdover processes. This is the length of time the reference oscillator was not locked to GPS. The
time units are seconds. The first number in the response is the holdover duration. The duration units
are seconds, and the resolution is 1 second. If the Receiver is in holdover, the response quantifies the
current holdover duration. If the Receiver is not in holdover, the response quantifies the previous
holdover. The second number in the response identifies the holdover state. A value of 0 indicates the
Receiver is not in holdover; a value of 1 indicates the Receiver is in holdover.
3.5.3 SYNChronization:HOLDover:INITiate
The command will place the unit into a forced holdover state, while still indicating the difference
between the internal 1PPS generated by the OCXO and the GPS generated 1PPS. This command is
useful to measure the OCXO drift when in holdover. Please note that the Time Interval Counter is
limited to +/-2000ns display range. The time interval difference may be displayed with the SYNC?
command.
3.5.4 SYNChronization:HOLDover:RECovery:INITiate
This command terminates a manual holdover that was initiated with the SYNC:HOLD:INIT
command, and return the unit to normal GPS locking mode.
3.5.5 SYNChronization:TINTerval?
This query returns the difference or timing shift between the FireFly-1A 1 PPS and the GPS 1 PPS
signals. The resolution is 1E-10 seconds.
3.5.6 SYNChronization:IMMEdiate
This command initiates a near-instantaneous alignment of the GPS 1 PPS and Receiver output 1 PPS.
To be effective, this command has to be issued while not in holdover.
3.5.7 SYNChronization:FEEstimate?
This query returns the Frequency Error Estimate, similar to the Allan Variance using a 1000s
measurement interval and comparing the internal 1PPS to GPS 1PPS offset.
Values less than 1E-012 are below the noise floor, and are not significant.