HP 8642A Operation And Calibration Manual page 291

Model 864 2A/B
Performance Tests
PERFORMANCE TESTS
5. Set the HP 8642 to 10.0 MHz then 0 dBm amplitude by incrementing
the amplitude in 10 dB steps.
Using the oscilloscope, verify that no large AC signal is
present. If AC is present the mixer input signals are not
at the same frequency and spectrum analyzer damage
may result.
6. On the HP 8642, enter SPCL 250. View the signal in the dc coupled
mode on the oscilloscope. Use the HP 8642 knob to adjust the de
level on the oscilloscope as close to zero as possible. This sets the two
input signals to the mixer in phase quadrature (90 degrees out of
phase).
7. View the trace and note the average noise leveL
8. The actual phase noise is calculated from the reading obtained in step
6 by
applying the following corrections:
a. Subtract the reading from step 4 to convert the reading to
units of dBc.
b.
Add -63.5 dB. (-50 dB for 8642 attenuator change, ~10
dB
for
1
Hz bandwidth normalization, -6 dB for single side band
con version,
+
2.5 dB to correct for the Log shaping and average
detection.)
9. Phase noise should be -125 dB or lower.
-125 dBc _ _ _ _
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