HP 8901B - Page 120

54
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.