HP 8568B manual X10

12. Time Base Adjustment (SN 2848A to 3217A05567)

The A27A2 10 MHz Quartz Crystal Oscillator (HP P/N 1081 l-601 11) typically reaches its specified aging rate again within 72 hours after being switched off for a period of up to 30 days, and within 24 hours after being switched off for a period less than 24 hours. If extreme environmental conditions were encountered during storage or shipment (i.e. mechanical shock, temperature extremes) the oscillator could require up to 30 days to achieve its specified aging rate.

Replacement oscillators are factory-adjusted after a complete warmup and after the specified aging rate has been achieved. Readjustment should typically not be necessary after oscillator replacement, and is generally not recommended.

1.Set the rear-panel FREQ REFERENCE switch on the spectrum analyzer RF Section to INT.

Note The + 22 Vdc STANDBY supply provides power to the heater circuit in the A27 10 MHz Frequency Standard assembly whenever line power is applied to the RF Section. This allows the A27 10 MHz Frequency Standard oven to remain at thermal equilibrium, minimizing frequency drift due to temperature variations. The OVEN COLD message should typically appear on the spectrum analyzer display for 10 minutes or less after line power is first applied to the RF Section.

Note The rear-panel FREQ REFERENCE switch enables or disables the RF Section +20 Vdc switched supply, which powers the oscillator circuits in the A27 10 MHz Frequency Standard. This switch must be set to INT and the spectrum analyzer must be switched ON continuously (not in STANDBY) for at least 72 hours before adjusting the frequency of the A27 10 MHz Frequency Standard.

2.Set the LINE switch to ON. Leave the spectrum analyzer ON (not in STANDBY) and undisturbed for at least 48 hours to allow the temperature and frequency of the A27 10 MHz Frequency Standard to stabilize.

3.Press [ml TRACE B (CLEAR-WRITE)g to turn off the display. This prolongs CRT life while the spectrum analyzer is unattended. To turn the CRT back on press (SHIFT] TRACE B (MAX HOLD)h.

4.Connect the (Cesium Beam) Frequency Standard to the Frequency Counter’s rear-panel TIMEBASE IN/OUT connector as shown in Figure 3-54.

5.Disconnect the short jumper cable on the RF Section rear panel from the FREQ REFERENCE INT connector. Connect this output (FREQ REFERENCE INT) to INPUT A on the Frequency Counter. A REF UNLOCK message should appear on the CRT display.

6.Set the Frequency Counter controls as follows:

INPUT	. . . . . . . . . . . . . . .	. . . A
ATTENUATION	. . . . . . . . . . . . . . . .	x10
DC Coupled	. . . . . . . . . . . . . . . .	OFF
1 MR input impedance		OFF
AUTO TRIG	. ..__	ON
100 kHz FILTER	_	OFF

3-100 Adjustments