Question

How does electromagnetic waves carry digital data?

Answer 1

Electromagnetic waves

1. Electromagnetic waves are the type of transverse waves that can travel through any medium or vacuum by mutually generating electric and magnetic fields.
2. Light is an example of an electromagnetic wave.

Digital data through electromagnetic Wwves

1. An information signal should be first converted into an electromagnetic signal before transmission because wireless transmission takes place using electromagnetic waves.
2. Electromagnetic waves are converted into digital data using the concepts of the sampling theorem.
3. The electromagnetic waves consist of both electric and magnetic fields.
4. Electromagnetic waves can travel long distances in space.
5. The electromagnetic signals are also called radio frequency (RF) waves.
6. The oscillatory EM waves are sinusoidal and their frequency is measured in $Hz$.
7. The frequency of EM signals can be very low or extremely high.
8. The entire frequency range of electromagnetic waves is called the electromagnetic spectrum.
9. These frequencies are applied in the radio of TV broadcasting as well.

Digital Communication:

1. Discrete information source: In the case of digital communication, the information source produces a message signal which does not continuously vary with time. Rather the message signal is intermittent with respect to time. The output of discrete information sources such as a teletype or the numerical output of a computer consists of a sequence of discrete symbols or letters. An analog information source may be transformed into a discrete information source through the process of sampling and quantizing.
2. Source encoder and decoder: The symbols produced by the information source are given to the source encoder. These symbols cannot be transmitted directly. They are first converted into digital form (i.e., binary sequence of 1's and 0's) by the source encoder. Each binary '1' and '0' is known as a bit. The group of bits is called a codeword. The source encoder assigns codewords to the symbols. For each distinct symbol, there is a unique codeword.
3. Channel Encoder and Decoder: After converting the message or information signal in the form of the binary sequence by the source encoder, the signal is transmitted through the channel. The communication channel adds noise and interference to the signal being transmitted. Hence errors are introduced in the binary sequence received at the receiver end.
4. Digital Modulators and Demodulators: In the process of modulation, the baseband signal is translated i.e., shifted from low frequency to high frequency. This frequency shift is proportional to the frequency of the carrier. Now, if the modulating signal is digital (i.e., binary codewords), then digital modulation techniques are used. The carrier signal used by digital modulators is always a continuous sinusoidal wave of high frequency. In fact, the digital modulators map the input binary sequence of 1's and 0's to the analog signal waveforms.
5. Communications Channel: The connection between transmitter and receiver is established through a communication channel. The communication can take place through wirelines, wireless or fiber-optic channels. The other media such as optical disks, magnetic tapes, disks, etc., may also be called a communication channel since they can also carry data through them.