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Unformatted text preview: 1-1YEDITEPE UNIVERSITY ENGINEERING FACULTY COMMUNICATION SYSTEMS LABORATORY EE 351 – COMMUNICATION SYSTEMS I EXPERIMENT 1: AMPLITUDE MODULATIONObjective: Definition and modeling of two of the Amplitude Modulation (AM) types – DSBSC (Double Side Band Supressed Carrier) and DSB (Double Side Band). Equipment: ¾Multiplier Module ¾Audio Oscillator Module ¾Master Signals Module ¾Scope Selector Module ¾Variable DC Supply Module ¾Adder Module ¾Oscilloscope General Information: Modulation is a process that modifies one or more parameters of a signal according to another signal. The modulated signal is called carrier signaland principally its frequency is much higher than the modulating signal in order to protect the original message signal (modulating signal) from the channel distortions. In AM, the amplitude of the carrier is modulated by the message signal. Double Sideband Suppressed Carrier (DSBSC) AM Signals A DSBSC signal is defined as: ( ) ( ) ( )ttEtXcmDSBSCωωcoscos.=(1.1) In equation (1.1), mωand cωare the angular frequencies of the message signal and the carrier signal respectively (cω&gt;&gt; mω). From the equation, it can also be seen that, the amplitude of the carrier signal is ( )tEmωcos.which is known as the envelopeof the DSBSCmodulated signal.Equation 1.1 can be expanded to give: ( ) ( )()( ) ( ) ( )tEtEttEmcmccmωωωωωω++−=cos.2/cos.2/coscos.(1.2) Equation (1.2) shows that the product is represented by two new signals, one on the sum frequency (cω+mω), and one on the difference frequency (cω- mω) in the frequency 1-2spectrum. These two frequency components are located close to the frequency spectrum....
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- Spring '05