GPS disciplined oscillators are crystal controlled. This is
true of the HP GPS receivers like the Z3801A and Z3816A. However,
Datum offers a choice between either crystal or rubidium oscillators.
The Datum System2000 is a second generation GPS based Time and
Frequency System. The use of a rubidium oscillator allows for
improved holdover performance should the GPS signal be lost.
The System2000 is also designed to provide the user with a variety
of plug-in option circuit boards for different applications.
receiver is an excellent performer, especially so in its rubidium
variant with the Efratom LPRO-101 oscillator.
System2000 Basic Specifications
Type: 6-channel C/A-Code-Receiver, tracks up to 6 satellites
continuously. An active amplified antenna is required.
8 x 10-13 Frequency Stability under Selective Availability
Rb-Oscillator Holdover Stability (Aging ca. 1.3 x 10-12
Rubidium Long Term Stability: 3.9 x 10-11 per month
1 pps Input: TTL into 50 Ohm for system check without
GPS (for ext. Sync) or for free running operation with external
1 pps Output: TTL into 50 Ohm
MHz Output: sine / 0.5 Vrms into 50 Ohm
Outputs A6 Warning Secondary-Alarm LED amber A7 Defect Primary-Alarm
LED red Number: 2 x changeover contacts / potential free Contact
Current Capability: 1 A
Supply: 38 to 74 Vdc (48 Vdc nominal) or 230 Vac Power:
Typical 30 W, max. 120 W (warm-up)
Temperature: 0° C to +45° C (Unit) -55° C to +85° C (Antenna)
Dimensions: 483 x 132. x 320 mm / w x h x d (about 19
x 5 x 12 inches)
150 Baud to 9600 Baud (hardware handshake, cable detail
front panel keypad, LED indicators, and LCD status indicator
rear panel is configured to provide for numerous user options.
The System 2000 is a modular design. The basic system provides
add-on capabilities to satisfy customer
needs for specific frequencies and varying numbers of outputs.
Up to 24 BNC and four Sub D9 outputs can be installed. The picture
below shows the a 48V version with additional 4 x 2.048kHz output
Datum System2000 has plenty of room inside the cabinet for optional
LPRO-101 Rubidium Oscillator
GPS disciplined rubidium oscillator provides a 10 MHz output.
The Efratom LPRO-101 is designed with a goal of ten years of
maintenance-free operation. According to Datum, each LPRO has
been designed to have enough rubidium fill in the lamp to last
for the required period, sufficient pulling range for the voltage
controlled oscillator, and adequate dynamic range of the rubidium
indicates the EFC control sensitivity is roughly 6 parts in
1E13 per millivolt, so relatively fine resolution is available
on the EFC software graph.
Efratom oscillator is a single circuit board design, has extensive
RFI shielding, and occupies one slot inside the receiver cabinet.
supplies basic control software for their System2000. This is
similar in appearance and function to the HP Satstat software.
Every command works normally in Terminal mode. Received data
is displayed in an output window. One phase measurement graph
is also generated that displays the last 500 values of phase
error from the unit's memory.
Software version D2k
receiver has significant differences from those of the HP or
Symmetricom families. Because of this, there is a special version
of GPSCon called GPSConD2k which is specifically designed to
work with this receiver. This software offers a high performance
alternative to that supplied by Datum.
are fundamental differences in the amount of information which
can be obtained from the Datum compared to the HP receivers.
Firstly, there is no information regarding satellites which
are not being tracked, only those which are currently being
used by the receiver. Secondly there is no predicted uncertainty
for holdover (free run) mode. Thirdly, the values for TI and
EFC are updated less frequently than a similar HP GPS receiver.
This has a modest impact on the appearance of a long term graph
of 48 hours or more. However, a short term graph is less detailed
than one from an HP receiver.
will produce a high quality graph of the electronic frequency
control, and the time interval between the 1 PPS GPS clock and
the 1 PPS locally generated clock. The number of satellites
being tracked is recorded as for an HP. The satellite map has
all the transit paths of the tracked satellites.
Note that GPSConD2k was written specifically for the Datum System2000,
and does not support a variety of additional HP style receivers
like the Z3801A. GPSCon Pro remains the software of choice for
HP GPS receivers.
Since the Datum System2000 has its own illuminated LCD display
and a keypad, it can be completely operated without a PC. However,
GPSConD2k adds another dimension to ones appreciation of this
fine receiver. A glance at the built-in long term receiver plots
will alert you to important changes in receiver performance.
Long term plots reveal subtle characteristics impossible to
determine with basic software.
Web-plots for the Datum System2000
is a built in feature that sends current receiver status plots
to an Internet server. This is useful for remote monitoring
applications. The screen capture below is from an actual Internet
The Datum receiver supports hardware handshaking only. The NULL
modem serial cable must have RTS and CTS, DTR and DSR, together
with TXD and RXD, connected as crossovers. In addition, each
end of the cable needs its DCD locally connected to DSR.
a receiver is moved, the stored position must be re-set. This
can be carried out by issuing a reset command (which deletes
all stored data) or by deleting the stored position only. The
stored position can be deleted by selecting the position display
screen, pressing "E" and selecting "yes". If the location is
incorrect, the unit will not lock to GPS.
Antennas with low power consumption trigger the "antenna feed
fault" error. This does not affect the running of the unit and
the alarm relay and LED can be disabled by setting the mask
on the error handling to ignore GPS errors. (One user noted
that he avoided the "antenna fault" condition by adding
a 470 ohm resistor threaded through a ferrite bead and then
connected to an SMA T piece. It still detects if the real antenna
to locate the System 2000 unit away from sources of heat or
cold and in a location with minimal temperature variation.
Some early units were sold under the Efratom name.
to Graham Leighton)