NOVATECH INSTRUMENTS 41450B Manual
5.3 For low-jitter 1pps inputs (<20ns), the approximate
tuning time constant will be 1,000 seconds. A typical
timing receiver system, such as the GPS1 (with approxi-
mately 100ns peak-peak 1pps jitter), requires a time con-
stant of approximately 10,000 seconds (about 3 hours)
for optimum tracking.
5.4 For noisier 1pps inputs, the time constant may in-
crease to 100,000 seconds. If the input is too noisy, the 1
PPS LOCK light will not illuminate.
5.5 Proper operation when tracking a 1pps signal is indi-
cated by all three front panel LEDs illuminated green.
NOTE:
Due to these long time constants necessary to track a
1pps input, temperature variations can cause fluctua-
tions in the relative phase of the 10MHz output and the
1pps output.
NOTE:
The f/f tracking range of the internal Rubidium
oscillator is approximately ±1x10-8. If your 1pps sources
in error, but within these limits, the 1450B will adjust to
your source. This allows multiple units to be synchro-
nized even in the absence of an absolute reference.
NOTE:
The auto-adaptive frequency adjustment has a resolution
of ±5.12x10-13.
CAUTION:
Do not connect the 1pps input and 1pps output on an
instrument together. This will force the instrument to
track a moving value and reach its adjustment limit.
5.6 The 1450B is configured for automatic self-
calibration. When continuously connected to a stable
1pps source, it will auto-save the disciplined frequency
value into non-volatile calibration memory every 24
hours. The last-saved value will be used at next power on
or when 1pps is lost. The 1pps output of a calibrated and
tracking 1450B has lower jitter than a typical GPS re-
ceiver making it suitable for use as a master oscillator for
further 1pps systems.
6.0 PERFORMANCE TEST& CALIBRATION
6.1 The performance test detailed below verifies that the
1450B accuracy is equal to the accuracy achieved imme-
diately after calibration. Prior to performing this test it is
recommended that the 1450B be calibrated.
NOTE:
There are no periodic user adjustments required for op-
eration of the 1450B. When necessary, calibration
should be performed “closed-case” using an external
1pps source.
NOTE:
The unit under test or calibration must remain undis-
turbed during the calibration period. Changes in envi-
ronmental conditions (temperature, electric field, mag-
netic field or physical orientation) affect the calibration.
If possible, calibration should be performed at the appli-
cation site.
6.2 Calibration: Calibration of the 1450B should be per-
formed “closed-case” using an external 1pps source.
Closed-case calibration is obtained by connecting the
1450B 1pps input to a known stable and accurate (better
than 1 x 10^11) 1pps source. Verify that the three front
panel LEDs are all illuminated green. A stable 1pps
source will allow this illumination within 15 minutes
after connection. Leave the unit tracking the 1pps exter-
nal signal in a stable environment for a minimum of 5
days. During this time the internal auto-adaptive algo-
rithm will measure and qualify the 1pps source, adjusting
the frequency to the long term average of the 1pps
source. When continuously connected to a stable 1pps
source, the 1450B will auto-save the disciplined frequen-
cy value into non-volatile calibration memory every 24
hours.
NOTE:
Calibration and verification of the frequency and fre-
quency stability of the 1450B requires a laboratory envi-
ronment of 23oC ±3oC.
