
Model 8640B
TM 9-4935-601-14-7&P
PERFORMANCE TESTS
4-12. FREQUENCY ACCURACY AND FINE TUNE TEST (Cont'd)
DESCRIPTION:
Frequency accuracy is checked (using the Signal Generator's internal reference) by comparing the generator's counter
indication to the frequency reading on an external frequency counter. The fine tune range is also checked with the
external counter.
EQUIPMENT:
Frequency Counter ................................................................................... HP 5327C OPT H49
PROCEDURE:
1.
Connect generator's auxiliary RF output jack (located on rear panel) to frequency counter's input after setting
Signal Generator's controls as follows:
COUNTER MODE:
EXPAND ................................................................................ X100
LOCK........................................................................................ Off
Source ..................................................................................... INT
AM............................................................................................................................................................ OFF
FM............................................................................................................................................................ OFF
RANGE .......................................................................................................................................... 32-64 MHz
FREQUENCY TUNE ........................................................................................................................... 50 MHz
RF ON/OFF................................................................................................................................................ON
2.
Allow Signal Generator and frequency counter to stabilize for two hours.
3.
Set frequency counter time base to give at least one more digit resolution than the generator's counter. The
difference in reading between the two counters should be <110 Hz (2 ppm + last digit uncertainty of 10 Hz).
__________________________ 110 Hz
4.
Set COUNTER MODE EXPAND to X10 and LOCK to ON. Allow one minute to acquire phase lock. Increase the
frequency counter resolution by 10. The difference in counter readings should be <100 Hz (2 ppm).
__________________________ 100 Hz
5.
Note frequency counter reading. Turn TIME BASE VERN control ccw until it just leaves the detent position. The
frequency counter should now read >1 kHz (>20 ppm) higher than the reading noted above.
1 kHz ___________________________
6.
Turn TIME BASE VERN fully ccw. The frequency counter should now read >1 kHz (>20 ppm) lower than the
reading first noted in step 5.
1 kHz ___________________________
4-4
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