Doppler Effect and Communication System

Doppler Effect

Doppler effect is a common phenomenon that we observe in our everyday life. The siren from the ambulance is heard louder as the ambulance comes closer to where we are standing and it fades away as the ambulance goes away from us. This effect is called the Doppler effect. This effect is observed in both sound waves and light waves.

The Doppler effect is the change in wave frequency when there is a relative motion between the source and the observer. When the source and the observer are moving relative to each other, the frequency of wave heard by the observer is different from the actual frequency of the wave. This effect is not caused by the actual change in the frequency of the source.

Doppler Effect Formula

The general formula for the doppler effect is given by

f  = () f0

Here f is the apparent frequency

f0 is the actual frequency

c is the propagation speed of waves in the medium

Vr is the velocity of the observer

Vs is the velocity of the source

Application of Doppler Effect

  • Doppler effect can be used to find the velocity of a star or a galaxy. When the light from the star is examined the spectrum will have many colours. If the star approaches the earth the spectral lines move towards the violet end of the spectrum and indicates an increase in frequency. If the star recedes from the earth the shift of spectral line will be towards the red end of the spectrum and indicates a decrease in frequency.
  • Doppler effect is used in Radar (Radio detection and ranging). The radio transmitter will send short pulses of electromagnetic radiation and radio receiver will receive the echo of the electromagnetic radiation from the object on its way. If the object (aircraft) is approaching then the reflected wave will have a higher frequency than the transmitted wave. If the object is moving away frequency decreases.

Communication Systems

The process by which a signal is transmitted and received is called communication. The major elements of the communication system are the transmitter, channel and the receiver. The elements can be further listed as

Input Messages: The input message signal can be music, video, data etc

Input Transducer: The input message can be in any form but for transmission, it should be converted to electrical energy. The transducer does the work of converting the input message into electrical energy.

Modulator: The original message or signal cannot be transmitted over a large distance because of its low frequency and amplitude. A carrier wave with high frequency and amplitude is superimposed with the signal. This process is called Modulation.

Transmitter: It converts the signal to be suitable for transmission through the medium.

Antenna: This is a device that receives and radiates electromagnetic waves. The antenna propagates the signal through the air.

Channel: The channel refers to the medium through which the signal propagates. The medium can be wire, cables etc.

Receiver: This is the arrangement that extracts the signal from the transmitter at the output end of the medium.

Demodulator: This is the reverse process of modulation. Demodulator separates the message signal from the carrier wave.

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