12. Time Base Adjustment (SN 2840A and Below, also 3217A05568 and Above)

Procedure Note

Note

The spectrum analyzer must be ON continuously (not in STANDBY) for at least 72 hours immediately prior to oscillator adjustment to allow both the temperature and frequency of the 10 MHz Quartz Crystal Oscillator to stabilize. Adjustment should not be attempted before the oscillator is allowed to reach its specified aging rate. Failure to allow sufficient stabilization time could result in oscillator misadjustment.

The A27Al 10 MHz Quartz Crystal Oscillator (HP P/N 0960-0477) will typically reach its specified aging rate again within 72 hours after being switched off for a period of up to 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.

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

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 (SHIFT) 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 m TRACE B C-HOLD) h.

4.Connect the (Cesium Beam) Frequency Standard to the Frequency Counter’s rear-panel TIMEBASE IN/OUT connector as shown in Figure 3-52.

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.

3.96 Adjustments