HP 8901B Operation And Calibration Manual page 120

5 4
RF Frequency and Frequency
Error
Frequency Offset Mode
This procedure demonstrates how the
HP
8901Bs Frequency
Offset Mode allows you to measure input signals above 1300 MHz
using an external oscillator and mixer.
(This
is one of three
techniques available for extending the RF frequency range of
the HP 8901B. The other two are
also
shown in this chapter.)
Diagram 5-1 shows the setup for this down-conversion technique.
MIXER
SIGNAL SOURCE
HP
89018
LOCAL
OSCILLATOR
Diagram
5-1. Setup for Frequency
Down Conversion
1 .
2.
3.
4.
5.
6.
7.
Set the signal source to the desired frequency at an amplitude
of about -5 dBm. (The optimum level
will
depend on the mixer
being used; select a level that will prevent mixer compression.)
Set the external
LO
to equal the output frequency of the
signal source plus 120.53 MHz. (For instance, if the signal source
frequency
was 2.5 GHz, the LO should be set to
2620.53 MHz.)
This
positions the HP 8901Bs internal IF in the center of a tuning octave.
Set the output level of the external
LO
to
+8
dBm.
Press
the
AUTOMATIC OPERATION
key and then key in 27.3
SPCL,
the external
LO
frequency, and the MHz key on the
HP
8901B. If
you make a mistake, press the CLEAR key and re-enter the keystrokes.
Manually tune the
HP
8901B to the expected frequency of the signal
source by keying in the source frequency and then pressing the
MHz
key.
The Manual Tuning Mode is always the right choice for this measurement
technique.
Now
select the desired measurement on the
HP
890lB. If you are making
RF
Power or Tuned RF Level measurements, the calibration factors for
the Sensor Module that you are using need to be stored in the Frequency
Offset cal factor storage table. Refer to Appendix B for the storage procedure.
When you want to exit the Frequency Offset Mode, key
in
27.0
SPCL.
If you wish to re-enter the Frequency Offset Mode and maintain
the same external LO frequency set in step
4,
key in 27.1 SPCL.