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Thông tin thiết kế mạch P2

AMPLITUDE MODULATED RADIO TRANSMITTER A radio signal can be generated by causing an electromagnetic disturbance and making suitable arrangements for this disturbance to be propagated in free space. The equipment normally used for creating the disturbance is the transmitter, and the transmitter antenna ensures the efficient propagation of the disturbance in free space. To detect the disturbance, one needs to capture some finite portion of the electromagnetic energy and convert it into a form which is meaningful to one of the human senses. | Telecommunication Circuit Design Second Edition. Patrick D. van der Puije Copyright 2002 John Wiley Sons Inc. ISBNs 0-471-41542-1 Hardback 0-471-22153-8 Electronic 2 AMPLITUDE MODULATED RADIO TRANSMITTER 2.1 INTRODUCTION A radio signal can be generated by causing an electromagnetic disturbance and making suitable arrangements for this disturbance to be propagated in free space. The equipment normally used for creating the disturbance is the transmitter and the transmitter antenna ensures the efficient propagation of the disturbance in free space. To detect the disturbance one needs to capture some finite portion of the electromagnetic energy and convert it into a form which is meaningful to one of the human senses. The equipment used for this purpose is of course a receiver. The energy of the disturbance is captured using an antenna and an electrical circuit then converts the disturbance into an audible signal. Assume for a moment that our transmitter propagated a completely arbitrary signal that is the signal contained all frequencies and all amplitudes . Then no other transmitter can operate in free space without severe interference because free space is a common medium for the propagation of all electromagnetic waves. However if we restrict each transmitter to one specific frequency that is continuous sinusoidal waveforms then interference can be avoided by incorporating a narrow-band filter at the receiver to eliminate all other frequencies except the desired one. Such a communication channel would work quite well except that its signal cannot convey information since a sinusoid is completely predictable and information by definition must be unpredictable. Human beings communicate primarily through speech and hearing. Normal speech contains frequencies from approximately 100 Hz to approximately 5 kHz and a range of amplitudes starting from a whisper to very loud shouting. An attempt to propagate speech in free space comes up against two very severe obstacles. .