Figure 2-9 Fm Deviation Test Setup - Agilent Technologies 8560E User Manual

Making Measurements
Example 3: Modulation
The following equation also determines percentage of modulation using
amplitude units in volts:
Frequency Modulation
This section contains general information about frequency modulation,
as well as a procedure for calculating FM deviation using a spectrum
analyzer.
For sinusoidal modulation where either the modulation frequency or
the FM deviation can be varied, the spectrum analyzer can be used to
accurately set up a modulation index corresponding to a Bessel null.
The following example illustrates how to verify the FM deviation
accuracy of a signal generator with FM capability. We will use a carrier
frequency of 100 MHz and test for FM deviation accuracy at a 25 kHz
rate using the modulation index for the first carrier null (2.401). Figure
2-9 illustrates how to set up the equipment for this measurement.
Figure 2-9 FM Deviation Test Setup
1. Connect the signal source to the spectrum analyzer INPUT 50Ω. Set
2. Press
62
where A = sideband amplitude, in volts
s
A = carrier amplitude, in volts
c
the source to 100 MHz.
to begin with the spectrum analyzer in a preset state
PRESET
and change the settings as follows:
a. Set center frequency to 100 MHz.
b. Set span to 100 kHz.
c. Set resolution bandwidth to 1 kHz.
d. Set video bandwidth to 1 kHz.
×
2 A 100
s
M = ----------------------- -
A
c
Chapter 2