HP 8901B Operation And Calibration Manual page 232

Operation
Model 8901B
HP-I8 PROGRAM CODES
FREQ ERROR =
S5
MHz = MZ
MEASUREMENT TECHNIQUE
When the Modulation Analyzer is tuned, the IF signal is amplified and limited.
If manually tuned,
the RF input frequency is measured and compared to either the keyboard-entered frequency or to the
frequency measured after the MHz key is pressed. The frequency difference is displayed as frequency
error.
If the Modulation Analyzer is automatically tuned, two methods of determining frequency error
are used
0
When the input signal is greater than
2.5
MHz, the frequency of the actual IF signal is subtracted
from the selected IF frequency
(455
kHz or
1.5
MHz) to determine the frequency error.
0
When the input signal is less than
2.5
MHz, the input signal is passed directly into the IF without
down-conversion. When the signal is first located, the frequency is counted. When the FREQ
ERROR key is selected, this first-counted frequency becomes the reference. Subsequent frequency
counts are subtracted from this reference, and the results are displayed a s frequency error.
I
CO UNTE
RI
VOLTMETER
CONTROLLER AND DISPLAY
,
c
(LO)
p
I
;
08081
-
OSCILLATOR
~ ~~~~~~
RF Requency Error Measurement Block Diagram
COMMENTS
Down-Converted Signals
The down-converted RF input frequency must fall within the passband of the IF being used. For the
1.5
MHz IF, the passband is approximately
3
MHz wide. For the
455
kHz IF, the passband is approximately
200 kHz wide.
3-122
RF Frequency Error