External Reference; Operational Verification - HP 3585A Service Manual

Operation Overview
3·5. External Reference
For applications requiring optimum frequency accuracy, the 3585A can be phase locked to
an external frequency standard. The external reference frequency must be 10 MHz or any
subharmonic down to IMHz ( ± 5 ppm); and the amplitude must be within the range of 0
dBm to + 1 5 dBm (50 ohms). The frequency accuracy of the external reference may be
substituted for the Oven Reference time coefficient in the Counter and Manual frequency­
accuracy specifications . To avoid performance degradation, the phase noise and spurious
content of the external reference signal must be at least - 1 10 dBc (1 Hz) relative to 1 0
MHz) at a 20 H z to 1 kHz offset .
To use an external reference:
1 . Remove the jumper from between the rear-panel OVEN REF OUT and EXTER­
NAL REF IN connectors.
(To keep from losing the jumper, you may connect one end of it to any
unused rear-panel connector.)
2. Using a shielded cable equipped with BNC connectors, connect your external
reference to the EXTERNAL REF IN connector.
(When the reference is initially connected, the beeper will sound and
the "L.O. UNLOCKED" message will appear on the screen. The
message will continue to be displayed until the master oscillator is pro­
perly phase-locked to the external reference.)
3·6. Operational Verification
The 3585A automatically performs an internal operational verification test and calibration
during its turn-on sequence and also when the
that most of the analog and digital circuitry is operating properly; but it does not verify that
the 3585A meets its published specifications . In the event of a test failure, the instrument's
beeper will sound and, in most cases, a Calibration Error Code or failure message will ap­
pear on the CRT screen.
The beeper will sometimes sound as a result of the local oscillator
being unlocked during the instrument's turn-on sequence; but this
initial «beep " does not constitute a test failure. To per form the
verification test, allow the instrument to warmup for about two
minutes and then press
the instrument is either defective or in need of ad justment. Con­
tact a qualified service technician or return the 3585A to -hp- for
service.
3-4
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key is pressed. This internal test verifies
NOTE
. I f this causes the beeper to sound,
Model 3585A