21. Frequency Reference Error Test

21.Frequency Reference Error Test

Related Adjustment Time Base Adjustment

Specification Aging Rate

<l x 10eg/day and ~2.5 x 10m7 year; attained after 30 days warmup from cold start at 25°C.

Temperature Stability

<7 x lo-’ 0” to 5E9’C. Frequency is within 1 x lo-” of final stabilized frequency within 30 minutes.

Description The frequency of the spectrum analyzer time base oscillator is measured directly using a frequency counter locked to a frequency reference which has an aging rate less than one-tenth that of the time base specification. After a 30 day warmup period, a frequency measurement is made. The analyzer is left undisturbed for a 24-hour period and a second reading is taken. The frequency change over this 24-hour period must be less than one part in 10’.

Note This test requires that the spectrum analyzer be turned on (not in STANDBY) for a period of 30 days to ensure that the frequency reference attains its aging rate. However, after aging rate is attained, the frequency reference typically attains aging rate again in 72 hours of operation after being off for a period not exceeding 24 hours.

Care must be taken not to disturb the spectrum analyzer during the 24-hour test interval, since the frequency reference is sensitive to shock and vibration. The frequency reference should remain within its attained aging rate if the instrument is left on, the instrument orientation with respect to the earth’s magnetic field is maintained, and the instrument does not sustain any mechanical shock. Frequency changes due to orientation with respect to the earth’s magnetic field and altitude changes will usually be nullified when the instrument

is returned to its original position. Frequency changes due to mechanical shock will usually appear as a fixed frequency error.

The frequency reference is also sensitive to temperature changes; for this reason the ambient temperature near the instrument at the first measurement time and the ambient temperature at the second measurement time should not differ by more than 1°C.

Placing the spectrum analyzer in STANDBY mode turns the instrument off while continuing to provide power for the frequency reference oven, helping to minimize warmup time. However, the frequency reference must be on to attain its aging rate.

Performance Tests 2 - 67