HP 70427A User Manual page 128

NOTE
Millimeter Phase Noise Measurement System Control
Step 4 - Adjust mixer bias if necessary
If mixer bias was enabled in step 3 adjust the mixer bias current for
maximum signal level from the harmonic mixer as measured at the
downconverter's IF output.
1. Press the
70427A Parms
a. Connect a spectrum analyzer to the downconverter's RF
ANALYZER output.
b. Move the cursor to the
c. Select IF with the left/right arrow keys.
2. Set the downconverter's IF gain to 0 dB. This is to insure that the IF
amplifier won't be driven into compression.
a. Move the cursor to the IF Gain line.
b. Select 0 dB with the left/right arrow keys.
3. If the DUT's output power is adjustable, set it for a harmonic mixer
input level that is just below the point where the signal starts being
compressed (as indicated by the RF spectrum analyzer).
4. Adjust mixer bias for a minimum IF signal measured by the spectrum
analyzer.
a. Move the cursor to the
b. Adjust the bias level with the Left/Right arrow keys.
Repeat these steps for maximum IF output measured on the RF spectrum
analyzer.
Step 5 - Autorange the downconverter's IF gain
1. Press the softkey
Done
2. Press the
Autorange downconverter
Step 6 - Verify beatnote and proceed
If the reference source is under user control adjust its frequency, if necessary,
to get a beatnote less than 5% of the peak tuning range. If the reference
source is under system control it will be tuned automatically.
After the beatnote is within the limits the system asks for proceed with the
measurement.
When the downconverter is configured for mm operation don't apply a
high-level microwave signal to the input. Change the mode back to
press the
INSTR PRESET
softkey on the HP 3048A controller.
Spectrum Analyzer View
mm Band Mixer Bias
softkey.
key. This will protect the IF amplifier from damage.
HP 70427A/HP 70428A User's Guide 3-29
Downconverter Operation
line.
line.
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