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EXPERIMENT 4

AMPLITUDE SHIFT KEYING (ASK)

1. ObjectiveGeneration of ASK modulated signals.

2. General InformationAmplitude shift keying ASK is a modulation process, which imparts to a sinusoid two

or more discrete amplitude levels.

If the base band signal (before modulation) is unipolar (ones (1) and zeros (0)), a simpleon-off keying can be applied. The on corresponds to code 1, and the off

corresponds to code 0. The ASK wave formats are illustrated in Figure 1.

Production of ASK Signal

An ASK signal can be produced as shown in Figure 2.

s t

(t) =s(t)cos(0t)

ASK signal

~ cos( 0t)

Unipolar

binary

sequence

(message)

Figure 2. Generation of ASK signal

Figure 1. ASK waveform

s(t)

1 110

0 T 2T 4T3T

t

(t)

0

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For a binary signal 1, the ASK signal will become;

Acos(0t) , 0

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3. Experiment Set LabView software

4. Experimental Procedure Create a modulating sine-wave signal using LabView software functions so that

display duration T and the duration between each sample dT can be changed

externally by the user. Do not use simulate signal function of LabView to

generate the sine-wave.

The Base-band signal to be ASK modulated will be provided as a sub-vi by thelaboratory assistant. There will be two kinds of pulse series in the provided sub-vi.

One of them is a simple square wave (1 0 1 0 1 0 ), and the second one is

created by the random sequence of 1s and 0s. In both types the pulse width is

selected as 100 samples. Just connect the T and dT variables and the constant

sample quantity to the given sub-vi, which you will insert on the block diagramwindow you design.

Display both sine-wave signal and pulse sequence signal in one waveform graphon the front panel of the vi file you design.

Design the remaining part of the vi file so that the sine-wave will be displayedduring the 1s of pulse series. While the pulse series take the value of 0, the sine

wave should not be displayed during the pulse. The final waveform will be called

as ASK modulated signal.