Spectrum analyzers with Option 003, Precision Frequency Reference, use an
The oven in the OCXO is powered only when the spectrum analyzer is powered on; there is no standby mode of operation. The OCXO’s oscillator operates only when the internal frequency reference is selected. Control line HEXT (High = EXTernal frequency reference) is inverted by A15U303B (Refer to the Al5 RF Assembly Schematic Diagram, Block M, sheet 2 of 4)
to generate LEXT. LEXT is sent to the OCXO via A15J306 pin 4. When LEXT is low, the oscillator in the OCXO will be turned off.
Replacement OCXOs are factory adjusted after a complete warmup and after the specified aging rate has been achieved. Thus, readjustment should typically not be necessary after OCXO replacement, and is generally not recommended.
If adjustment is necessary, the spectrum analyzer must be ON continuously for a minimum of 24 hours immediately prior to oscillator adjustment to allow both the temperature and frequency of the oscillator to stabilize. Failure to allow sufficient stabilization time could result in oscillator misadjustment.
Check operation of the A21 OCXO as follows:
1.Disconnect W49 (Coax 82) from A155305. Connect the output of W49 to the input of another spectrum analyzer.
2.Check that the fundamental frequency is 10 MHz and that the power level is 0 dBm
f3 dB. Also check that the harmonics are at least
3.If the OCXO has no output, check A15J306 pin 1 for +15 Vdc. Check A15J306 pin 4 for a
4.If A15J306 pin 4 is at a
10 MHz EXT INT until INT is underlined. A15J306 pin 4 should read a
Press 10 MHz EXT INT until EXT is underlined. A15J306 pin 4 should read a