HP 8901B

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.
(ked 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 hction 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 hction 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 is
not normally used and the RF input signal passes directly into the IF.
BLOCK DIAGRAM
VOLTMETER
IF IF
Cn U NTE R/
INPUT
RF ATTCLIIIATnD INPUT AIID/CIITCD I InniTCoC
I I
T-
U
.
I
IF Requency Measurement Block Diagram
IF Frequency 3-125