HP 8901B Operation And Calibration Manual page 234

Model 8901B
Operation
IF Frequency
FUNCTIONS
Special hnction 34 (IF Frequency)
DESCRIPTION
The Modulation Analyzer makes tuned (down-converted, heterodyned) measurements on its RF input
signal using one of two IF frequencies. Three combinations of tuning and
IF
selection are used:
1. When RF input signals less than 2 . 5 MHz are measured, the
RF
input signal passes directly into
the
IF' without down-conversion; that is, the RF input frequency and the IF
frequency are the
same. ( k e d measurements can be manually extended below 2 . 5 MHz. Refer
to RF Bequency
Zbning on page 3-115.)
2 . When RF input signals greater than 2 . 5 MHz, but less than 10 MHz are measured, the signal is
down-converted to a 455 kHz
IF.
3 . When RF input signals greater than 10 MHz are measured, the signal is down-converted
to a
1.5
MHz IF.
(Note
that special h c t i o n 3 can be used to select the
455
kHz IF. Refer to Filters, RF
and IF on page 3-229.)
Special hnction 34.0 enables the Modulation Analyzer to measure and display the IF frequency for
the signal being measured.
PROCEDURE
To measure the
IF
frequency, key in 34.0 SPCL.
MEASUREMENT TECHNIQUE
The
IF
signal, generated when the Local Oscillator and the RF input signal mix, is amplified by the
IF
Amplifier and FM Limiters and then counted. The IF frequency is displayed when Special h c t i o n 34
is used. When measuring
RF
input frequencies greater than 2 . 5 MHz, the Modulation Analyzer uses
either the 455 kHz or 1 . 5 MHz
IF.
For RF input frequencies less than 2 . 5 MHz, down-conversion i s
not normally used and the RF input signal passes directly into the
IF.
BLOCK DIAGRAM
VOLTMETER
IF IF
C n U
NTE R /
INPUT
R F
A T T C L I I I A T n D
INPUT
A I I D / C I I T C D I
I n n i T C o C
I I
T -
U
.
I
IF Requency Measurement Block Diagram
IF Frequency
3-125