HP 8901B

Operation Model 8901B
Action Regarding Frequency
Off set Control
Exit Frequency Offset Mode
Re-enter Frequency
Offset Mode
Display the External
LO Frequency
Enter and Enable the
LO Freauencv’
The following table summarizes the various Frequency Offset Control special functions:
Special Function Program Code
27.0 SPCL 27.0SP
27.1 SPCL 27.1 SP
27.2 SPCL 27.2SP
27.3 SPCL 27.3SP
Code HP-I8
~
‘After Special Function 27.3 is entered, enter the frequency of the LO (in MHz) Frequencies from 0 to
40700 MHz can be entered.
Having entered the appropriate LO frequency, either manually tune to the microwave input frequency
by pressing the appropriate numeric keys followed by the MHz key
or let the Modulation Analyzer
automatically tune to the input signal.
Perform instrument measurements as usual. Select DISPLAY FREQ (Blue Key, kHz t) to display the
microwave input frequency.
HP-IB PROGRAM CODES
All HP-IB codes for manipulating the frequency offset control using Special Function 27 are provided
in “Procedures”.
DISPLAY FREQ
= FR
MHz
= MZ
MEASUREMENT TECHNIQUE
The external LO mixes with the microwave input signal to create a difference frequency which is the
input to the Modulation Analyzer. The frequency of the microwave input signal must be within
1300
MHz of the external LO to be within the measurement range of the Modulation Analyzer. The LO
frequency
is manually entered by the operator using Special hnction 27.3. The Modulation Analyzer,
thereafter, uses that
LO frequency to compute the microwave input signal frequency regardless of the
actual frequency of the
LO.
If tuning is in the automatic mode, the Modulation Analyzer computes and displays the microwave
input frequency as
(frequency of LO)
- (frequency at INPUT).
If tuning
is manual, the Modulation Analyzer computes and displays the microwave input frequency as:
(frequency of
LO) f (frequency of INPUT).
The difference is computed when the manually-entered frequency is less than the
LO frequency. The
sum is computed when the frequency is greater. The sense (+ or -) of the math operation remains the
same regardless of the actual microwave input frequency, even
if automatic tuning is selected.
The displayed frequency is always based on the frequency actually at the Modulation Analyzer’s input
and not the manually-entered input frequency, which serves only to set the Modulation Analyzer’s
internal
LO. Manually entering a new microwave input frequency, entering a new LO frequency, or
initiating automatic tune always retunes the Modulation Analyzer.
When the manually entered LO frequency is displayed (Special Function 27.2), a minus (-1 sign
preceeding the frequency indicates that the math operation
is a sum.
3-226 Frequency Offset Control