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Model 8902A
Operation
IF Frequency
FUNCTIONS
Special Function 34 (IF Frequency)
DESCRIPTION
T h e Measuring Receiver makes tuned (down-converted, heterodyned) measurements o n its R F input
signal using o n e of two I F frequencies, Three combinations o f tuning and IF selection are used:
1. When RF input signals less than 2.5 MHz are measured, the R F input signal passes directly into
the I F without down-conversion; that is, the R F input frequency and the IF frequency are the
same. (Tuned measurements can be manually extended below 2.5 MHz. Refer to
RF
Frcqircwcy
Timing o n page 3-141.)
2. When R F input signals greater than
2.5
MHz, but less than 10 MHz are measured, the signal is
down-converted to
a
455 kHz IF. (The 455 kHz IF is also selected when making the Tuned RF
Level measurements; irrespective o f R F frequency.)
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 Function 3 can be used to select the
455 kHz
IF. Refer t o F i / / m ,
R F and IF o n page 3-259.)
Special Function 34.0 enables the Measuring Receiver t o measure and display the I F frequency for
the signal being measured.
PROCEDURE
To measure the I F frequency, key in 34.0
SPCL.
MEASUREMENT TECHNIQUE
The IF signal, generated when the Local Oscillator and the R F input signal mix, is amplified by the I F
Amplifier and FM Limiters and then counted. The IF frequency
is
displayed when Special Function
34 is used. When measuring RF inpiit frequencies greater than
2.5
MHz, the Measuring Receiver uses
either the 455 kHz o r 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.
3-151
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