HP 8901B Operation And Calibration Manual page 235

Operation Model
8901B
COMMENTS
Input/Output Status
When the instrument is measuring
IF
frequency, the signal at MODULATION OUTPUT/AUDIO
INPUT remains unchanged.
Relative Measurements
If
IF
frequency is to be displayed relative to a reference, enter the ratio reference using the RATIO key.
(Refer to Ratio on page 3-215.)
Frequency Resolution
Normally, the counter updates the display five times each second. For selection of other resolutions,
use Special b c t i o n 7. (Refer to RF Bequency Resolution on page 3-131.) Counter accuracy is the
reference accuracy f 3 counts.
IF Filter Selection
IF
filter selection is dependent on the selected
IF
Frequency. (Refer
to Filters, RF and IFon page 3-229.)
When using the
455
kHz IF on input signals with frequencies greater than 300 MHz, incidental AM
(that is, AM due to FM) increases substantially.
RF Input Frequency Calculation
The Modulation Analyzer determines the frequency of the RF input signal by counting the frequencies
of both the
IF
and LO and calculating their difference.
IF Frequency Accuracy
The
IF
frequency need not be exactly its nominal value in order to guarantee accurate modulation
measurements. Unless specifically overridden by Special Function 8 or DISABLE ERROR (Blue
Key,
RANGE
HOLD), Error Messages safeguard the measurements. (Refer to Error Message Disable
Control on page 3-233 and RF Bequency T h i n g on page 3-115.)
3-126 IF Frequency