Users manual
NR3700-O/G
Revision #:
A
Date:
9-13-16
Page #:
3 of 19
1.0 Overview
The NR3700-O/G is a GPS locked OCXO 10 MHz frequency reference with optional
PPS and RS232. The unit features Auto-Calibration such that the most recent
coefficients to compensate the OCXO for drift due to aging and/or temperature are
stored and applied to the OCXO during GPS loss of lock conditions. These coefficients
are updated after 8 hours of continuous GPS locked state. This effectively eliminates
long-term OCXO changes.
Options: RS232,TCXO, and Ultra Low Phase Noise OCXO
The RS 232 interface provides access to the NMEA-0183 data from the GPS at a baud
rate of 38.4K. The baud rate can be changed through the RS232 port using commands
described in Appendix A (Output Format Section).
The unit operates from power in the voltage range of -60 to +60 Vdc in three power
supply ranges that must be specified at purchase. There is also an AC power adapter
available.
The output is a 10 MHz sinewave at 4.5 dBm (0.38 Vrms). The output is short circuit
and transient protected.
PPS pulse is a LVCMOS signal and is also short and transient protected. The PPS has
an accuracy of 30 ns rms.
The Global Positioning System (GPS) transmits a wealth of data. The information is
routinely used for position and timing. This signal is what is used by all GPS disciplined
oscillators for master timing.
The first part of the process is acquiring the GPS satellites and deriving what is called
the PPS signal. This is a pulse that occurs once a second. Most GPS receivers will
specify an accuracy for the leading edge in the range of ~20 ns rms. Due to
atmospheric conditions, multi-path and other effects, there is considerable jitter on the
pulse. This pulse, with exceptional long-term accuracy of ~E-12, is the starting point for
the GPSDO.
The PPS is used to derive a 10MHz signal. As you can imagine, the algorithms for the
generation of the 10MHz are very sophisticated. You are, in effect, creating a 10MHz
waveform with frequency measured once a second by a waveform which has
considerable jitter.
