Tektronix SPG8000 Technical Reference page 31

Table 27: GPS timebase (cont.)
Characteristic
Stability when locked to GPS or
GLONASS (typical) 1
Accuracy when locked to GPS or
GLONASS 1
Accuracy in Holdover mode
(typical)
Clean Recovery Holdover Drift
(GPS mode only)
Clean Recovery Holdover Duration
(typical)
(GPS mode only)
Timing behavior when locked
(GPS mode only)
Frame Timing Accuracy in fixed
position mode (typical)
(GPS mode only)
Frame behavior on Relock (typical)
(GPS mode only)
Timebase offset during Relock
(typical)
(GPS mode only)
SPG8000 Specifications and Performance Verification
Performance requirements
Allan Deviation < 8 x 10 , measurement
–11
interval of 1, 10, or 100 sec in fixed position
mode.
±1 part in 10 averaged over 30 sec. After
9
20 min warm up and in fixed mode.
±2 parts in 10 from recent valid lock
9
frequency, Temp change of ±5 °C.
±10 parts in 10 for 0 to 50 °C.
9
±20 ms
35 days, must be in stable temperature
environment and have warmed up for
20 minutes before holdover.
Displays "Locked" if within 150 ns of absolute
time as detected by GPS or GLONASS
signal.
Outputs of any two units are typically timed
within 150 ns if both have good signal quality
and the same cable delay from antenna to
instrument.
Selectable between Jam Phase, Fast Slew
and Stay Legal.
In Stay Legal mode, will stay in spec as slew
with respect to frequency offset and drift
rate spec. If in fast slew or stay legal mode,
frames will slew back to the correct alignment
via timebase offset without jumping.
For stay legal mode, limited to less than
±0.2 ppm frequency offset, and limited to
change less than 0.02 ppm/sec.
Reference information
Note that this is for fixed mode and is a
function of base unit oscillator, satellite signal
quality from antenna, and GPS functionality.
For mobile mode, the Allan deviation is about
2 x 10 .
-10
Long term stability is set by the GPS, but
short term by the base unit.
Translates to 10 ns of drift per 1 sec that is
in holdover mode. This is a function of the
base unit oscillator.
Maximum amount of timebase drift that can
be corrected without disruption to video
timing.
Length of time that can be in stay current
holdover mode and recover without disruption
to syncs. Dependant on environment and
base unit oven oscillator stability. Translates
to 2 ns of drift per sec in holdover mode.
Frames Based on SMPTE 404 / TAI Epoch
Recovery from drift may take a long
time if configured for stay legal recovery
(approximately 300 sec per line of drift at
NTSC or PAL rates).
Fast Slew has limits of ±5 ppm offset and
0.5 ppm / sec.
Specifications
17