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Operation
Model
8902A
T h e following table summarizes the various Frequency Offset Control special functions:
Action Regarding Frequency
Offset Control
Exit Frequency
Offset Mode
Re-enter Frequency Offset Mode
Display the External
LO
Frequency
Enter and Enable
the
LO
Frequency.
Special Function
Program
Code
Code
HP-I8
27.0 SPCL
27.0SP
27.1 SPCL
27.1 SP
27.2 SPCL
27.2SP
27.3 SPCL
27.3SP
'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 t h e Measuring
Receiver automatically tune to the input signal.
Perform instrument measurements as usual. Select DISPLAY FREQ (Blue Key,
kHz
1)
to
display
the microwave input ryequency.
HP-IB PROGRAM CODES
All HP-IB codes for innnipdating the frequency offset control using Special Function
27
are provided
in "Procedures".
DISPLAY FREQ
=
FR
MHz
=
M Z
MEASUREMENT TECHNIQUE
T h e external LO mixes with the microwave input signal to create a difference frequency which is the
input to the Measuring Receiver. The frequency of the microwave input signal must be within
1300
MHz o f the external
LO to
be within the measurement range o f the Measuring Receiver. T h e LO
frequency is manually entered by the operator using Special Function
27.3.
T h e Measuring Receiver,
thereafter, uses that
LO
frequency to compute the microwave input signal frequency regardless o f
the actual frequency of the
LO.
If tuning is in the automatic mode, the Measuring Receiver computes and displays t h e microwave
input frequency as
(frequency o f LO) - (frequency at INPUT).
If tuning is manual, the Measuring Receiver computes and displays the microwave inpiit frequency
as:
(frequency of LO)
f
(frequency of INPUT).
T h e difference is computed when the manually-entered frequency is less than the LO frequency. T h e
sum is computed when the frequency is greater. T h e sense
(+
o r
-)
of the math operation remains
the same regardless of the actual microwave input frequency, even if automatic tuning is selected.
T h e displayed frequency is always based on the frequency actually at the Measuring Receiver's input
and not the manually-entered input frequency, which serves only to set the Measuring Receiver's
internal LO. Manually entering a new microwave inpiit frequency, entering a new LO frequency, o r
initiating automatic tune always retunes the Measuring Receiver.
When the manually entered LO frequency is displayed (Special Function
27.2),
a minus
(-)
sign
preceeding the frequency indicates that the math operation is a sum.
3-256
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