Symmetricom ET6000, User Manual

Page: 10 / 206

GENERAL INFORMATION
The L1 and L2 frequency is also modulated with a fifty-bit-per-second data stream providing
satellite ephemerides, system time, satellite clock behavior, and status information on all satellites.
The data message is contained in a data frame that is 1,500 bits long.
Ground based control/monitoring stations track the satellites and provide an upload several times
each day to provide a prediction of each satellites ephemeris and clock behavior for the next day’s
operation.
1.3 PRODUCT DESCRIPTION
The GPS Timing Unit operates on the civilian L-band (1575.42MHz) utilizing C/A (Coarse
Acquisition) code transmissions to monitor time and frequency data from the Navstar satellite
constellation. Time and frequency is determined from satellite transmissions and calculations
referenced to USNO (United States Naval Observatory) through the GPS Master Clock system.
This link provides traceability to USNO and all international time scales through the use of
publications from NIST (National Institute of Standards Technology), USNO, and BIPM (Bureau of
International Des Poids et Measurements) in Servres, France.
The unit automatically acquires and tracks satellites based on health status and elevation angle. In
the Stationary mode, time and frequency monitoring requires only one satellite, once accurate
position data has been acquired or entered, although the receiver will use as many satellites as
available. In “AUTO” mode, and the “Dynamic” mode, a minimum of four satellites are required
for the GPS Timing unit to do three dimensional (latitude, longitude, and altitude) position fixes.
The basic GPS Timing Unit configuration includes the GPS Main Module, an antenna/preamp and
a coaxial cable for interconnection. A corrected 1pps output signal and a 10MHz Sine Wave are
provided. An RS-232 I/O Port is also provided in the basic configuration which can be used to
control the unit as well to get data from the unit. The basic unit has an LCD Display and a
keyboard. It generates IRIG B Serial Time Code, and has the capability of measuring the time
interval difference between the GPS 1pps and an externally input 1pps (or it can measure an
external frequency input – Models ET6000 and ET6010 only). It contains an RS-232 printer port.
Optional features listed in Appendix C are available to meet specific requirements. Refer to the
GPS Option/Connector Configuration sheet located in this manual for the options supplied with this
instrument. The Option Descriptions are located in Appendix C.
Note: The GPS antenna and cable described in this manual have been replaced as described in
“Appendix D: Antenna Replacement Kit” on page D-1.
Symmetricom Inc ET6xxx ExacTime GPS TC & FG (Rev C) 1-3