HP 8901B Operation And Calibration Manual page 94

Extending Operation
2-7
Drifty Signal
A drifty or noisy input signal can cause the instrument to continuously
display four dashes (Auto Tuning mode) or display Error 01 (Manual Tuning
mode). Press the
TRACK
MODE
key to select the wide-IF-bandwidth
track mode function. Track Mode can be selected with either the Auto
or Manual tuning modes. Note that the Track Mode function reduces
the low frequency response of modulation measurements and increases
the level of residual modulation. (For details on the capabilities and
limitations of Track Mode operation, refer to Track Mode in this chapter.)
Frequency Overrange
There are three techniques for extending the HP 8901B's frequency
range above 1300 MHz: internal harmonic mixing, external local
oscillator and mixer down-conversion, and down-conversion with
a spectrum analyzer. All three techniques extend the measurement
capabilities of the HP 8901B to microwave frequencies. (Refer to
Chapter 5 for measurement examples using these tuning techniques.)
Frequency Underrange If the input frequency is below the HP 8901B's frequency measurement
range, the instrument
will
display Error 10. The specified low frequency
limit of the RF Frequency measurement is 150
kHz.
However, you
can extend this measurement range to 20 Hz by simply selecting the
Audio Counter. Connect your signal source to the MODULATION
OUTPUT/AUDIO INPUT port and press the
AUDIO INPUT
key (key
should remain lit). Press the gold S key and the
AUDIO
FREQ key. The
Audio Counter will accurately count input signals from 20 Hz to 250 kHz.
Unstable Signal
If you are measuring an input signal whose RF level does not remain
above -20 dBm to -25 dBm, (for example, a low level signal with
high-depth AM or a signal that is being pulsed on and o f f ) , select the
Manual Tuning mode by keying in the frequency of your input signal and
pressing the MHz key. In Manual Tuning mode, the instrument
will
remain
locked at the manually tuned frequency after the input signal is turned o f f .