
Model 8640B
TM 9-4935-601-14-7&P
PERFORMANCE TESTS
4-12. FREQUENCY ACCURACY AND FINE TUNE TEST (Cont'd)
7.
Set TIME BASE VERN to CAL (fully cw). Set COUNTER MODE LOCK to Off.
8.
Set FINE TUNE fully cw. Note frequency counter reading, then set FINE TUNE fully ccw. The frequency counter
should read >10 kHz (200 ppm) lower than the reading noted above.
10 kHz __________________________
4-13. FREQUENCY STABILITY VS TIME AND RESTABILIZATION TIME TEST
SPECIFICATION:
Stability vs Time (after 2 hour warmup): <10 ppm/10 min. (normal mode).
Restabilization Time (normal mode):
After frequency change: <15 min.
After band change: none.
After 1 min. in RF OFF mode: <10 min.
NOTE
Stability specifications for phase lock mode are determined by counter time base reference. See
the internal reference tests.
DESCRIPTION:
A frequency counter, digital to analog converter, and strip-chart recorder are used to measure the frequency drift after
warm-up and the restabilization time.
NOTE
For these tests, ambient room temperature and line voltage must not change.
Figure 4-1. Frequency Stability us Time and Restabilization Time Test Setup
4-5
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