Agilent Technologies 54503A Podręcznik Użytkownika Pobierz pdf (Strona 62)

100

101

62 Chapter2

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

the source to 100 MHz.

2. Press

PRESET to begin with the spectrum analyzer in a preset state

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.

where A

= sideband amplitude, in volts

= carrier amplitude, in volts

100×

------------------------=

1 2 ... 57 58 59 60 61 62 63 64 65 66 67 ... 715 716

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