Anritsu S113C Guide de l'utilisateur télécharger pdf (Page 75)

Site Master Spectrum Analyzer Features

AM/FM Modulation

Modulation is the process of translating some low frequency or baseband signal (voice, mu-

sic, or data) to a higher frequency. In the modulation process, some characteristic of a car-

rier signal (usually amplitude or frequency) is changed in direct proportion to the

instantaneous amplitude of the baseband signal.

The following procedure describes how to measure signals with AM and FM types of mod-

ulation. It shows how to tune the signal on the spectrum analyzer display.

Amplitude Modulation

Step 1. Reset the Site Master to the factory default settings if a known starting state is

desired.

If the unit is off, hold down the ESC/CLEAR key while pressing the ON/OFF

key.

If the unit is already on, press the RECALL SETUP key on the data keypad.

When the key is pressed, a Recall Trace selection box appears on the display.

Select setup location 0 to recall the factory preset state.

Step 2. Connect a signal source to the spectrum analyzer input.

Step 3. Set the source to a carrier frequency of 100 MHz, –25 dBm, with an amplitude

modulation of about 35 kHz at 10% modulation.

Step 4. Set the spectrum analyzer center frequency to 100 MHz. Set the span to 500

kHz.

Step 5.

To determine the frequency of the carrier, press the MARKER key and

M1 soft

key. Then press the

MARKER TO PEAK soft key to automatically turn marker

M1 on and set it to the center frequency.

Additional modulation information can be determined from the carrier signal and sideband.

For example, the difference between the carrier frequency and the sideband frequency can

be found by pressing turning on and positioning Marker M2 over an upper or lower side-

band frequency and pressing the

DELTA (M2-M1) soft key. Figure 5-1 shows the modulat-

ing frequency of 35 kHz as the value of delta Marker 2.

5-3

Chapter 5 Spectrum Analyzer Measurements

Figure 5-1. Amplitude Modulation

SgLabs

www.sglabs.it

email: [email protected]

tel. +39 0755149360

SgLabs

www.sglabs.it

email: [email protected]

tel. +39 0755149360

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Anritsu S113C Guide de l'utilisateur Page 75

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