The NR2310-O/G is a GNSS-locked OCXO 10 MHz frequency reference with
PPS and RS232. The unit features auto-calibration so 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 eight hours of continuous GPS locked state. This
effectively eliminates long-term OCXO changes.
The RS232 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 AC power 90 to 240 VAC or optional DC source in the
range -60 to +60 VDC (in three ranges). The DC option can be primary or a
secondary source.
The outputs are 10 MHz sinewave at 13 dBm (1.0 Vrms). The outputs are 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 unit may be ordered with the PPS level
at 3.3 or 5 VDC CMOS levels and are capable of driving a 50 Ohm load (units
manufactured. after March 2020).
The GNSS transmits a wealth of data. The information is routinely used for
position and timing. This signal is what is used by all GNSS disciplined oscillators
for master timing.
The first part of the process is acquiring the GNSS satellites and deriving what is
called the PPS signal. This is a pulse that occurs once per second. Most GNSS
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 per second by a
waveform which has considerable jitter.
To get a useful frequency reference, the jitter (phase noise) of the frequency
reference must be improved. A very low bandwidth phase locked loop is used to
lock a high performance 10 MHz OCXO to the synthesized disciplined 10 MHz.
