Model 8640B TM 9-4935-601-14-7&P
PERFORMANCE TESTS
4-44. INTERNAL REFERENCE DRIFT RATE (STABILITY) TEST (Cont'd)
NOTE
Any change in chamber temperature could make the instrument's drift rate vs voltage appear out
of specification.
9. Reset transformer to nominal line voltage. Set temperature controlled chamber to 150C. Wait two hours to allow
generator's internal reference to stabilize, then note its frequency.
10. Set temperature controlled chamber to 35°C. Wait two hours, then note the reference frequency. The frequency
change from the reading noted in step 9 should be <10.2 Hz (i.e., <2 ppm +1 digit counter ambiguity).
Temperature: 10.2 Hz
11. Note generator's internal reference frequency, connect coaxial short to RF OUTPUT, then again note reference
frequency. Except for the ± 1 digit count ambiguity, it should not have changed.
Load: (/) No Change
12. Remove coaxial short. Note internal reference frequency, set OUTPUT LEVEL switch one step ccw to +9 dBm, then
again note reference frequency. Except for the +1 digit count ambiguity, it should not have changed.
Level Change: (/) No Change
13. Note internal reference frequency, set FM switch to AC, then again note reference frequency. Except for the ± 1
digit count ambiguity, it should not have changed.
Mode Change: (A) No Change
4-45. PHASE LOCK RESTABILIZATION TIME TEST
SPECIFICATION:
Restabilization Time (phase locked mode): After frequency or band change, or after 1 min. in RF OFF mode; <1 min.
after relocking to be within 0.1 ppm of steady-state frequency.
DESCRIPTION:
A frequency counter, digital to analog converter, and strip-chart recorder are used to measure stability after relocking.
4-75
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