-This experiment can be regarded as optional,sine it requires some complex and costly test equipment,such as the spectrum analyzer,not always available within a school laboratory.
-Adjust the level of the modulating signal generator (P1) to half-way.Measure and record the amplitude of this modulating signal as well as the frequency.
-Measure and record the frequency of the carrier generator.
-Display the spectrum of the modulated wave by means of the spectrum analyzer.Record the frequencies and amplitudes of the three frequency components displayed.
-check the frequency relationship between modulating signal,carrier and modulated signal component frequencies by means of a simple calculation.
-Move the amplitude of the modulating signal from 0 to maximum and observe the consequent change in the signal spectrum as appearing at the wave analyzer.Observe that the side-frequency amplitudes change according to the amplitude of the modulating signal.This is consistent with the fact that the information contents of the AM modulated wave is related to the sidebands and not to the carrier.
-Readjust the modulating signal amplitude to a value allowing the maximum modulation index value without incurring in over-modulation or heavy linearity loss.To do this,proceed as alerady learnt in the preceding worksheets.Display the spectrum of the AM modulated wave by means of the wave analyzer again.
-Record the amplitudes of the three spectrum components.Check the following properties of AM waves:
-The amplitudes of the sidebands are equal (if the circuit is perfectly tuned)
-At 100% modulation index,the amplitudes of the sidebands are 1/2 the amplitudes of the carrier.This is the maximum amplitude that the sidebands can have without over-modulation.
-This experiment can be regarded as optional,sine it requires some complex and costly test equipment,such as the spectrum analyzer,not always available within a school laboratory.-Adjust the level of the modulating signal generator (P1) to half-way.Measure and record the amplitude of this modulating signal as well as the frequency.-Measure and record the frequency of the carrier generator.-Display the spectrum of the modulated wave by means of the spectrum analyzer.Record the frequencies and amplitudes of the three frequency components displayed.-check the frequency relationship between modulating signal,carrier and modulated signal component frequencies by means of a simple calculation.-Move the amplitude of the modulating signal from 0 to maximum and observe the consequent change in the signal spectrum as appearing at the wave analyzer.Observe that the side-frequency amplitudes change according to the amplitude of the modulating signal.This is consistent with the fact that the information contents of the AM modulated wave is related to the sidebands and not to the carrier.-Readjust the modulating signal amplitude to a value allowing the maximum modulation index value without incurring in over-modulation or heavy linearity loss.To do this,proceed as alerady learnt in the preceding worksheets.Display the spectrum of the AM modulated wave by means of the wave analyzer again.-Record the amplitudes of the three spectrum components.Check the following properties of AM waves: -The amplitudes of the sidebands are equal (if the circuit is perfectly tuned) -At 100% modulation index,the amplitudes of the sidebands are 1/2 the amplitudes of the carrier.This is the maximum amplitude that the sidebands can have without over-modulation.
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