how the modulation works in Electromagnetic waves

Modulation is a crucial technique in communication systems that allows information (such as audio, video, or data) to be transmitted over a carrier wave efficiently. Modulation involves varying one or more properties of the carrier wave, such as its amplitude, frequency, or phase, to encode the information. Here's how modulation works in detail:

1. Carrier Wave:

• A carrier wave is a high-frequency electromagnetic wave that serves as the "vehicle" for carrying the information. It typically has a constant frequency, amplitude, and phase.

2. Information Source:

• The information source provides the data or signal that needs to be transmitted. This can be an audio signal (e.g., voice or music), a video signal (e.g., a TV broadcast), or digital data (e.g., internet data).

3. Baseband Signal:

• The information source generates a baseband signal, which is the original signal that we want to transmit. The baseband signal usually has a lower frequency range and may contain both positive and negative components.

4. Modulation Process:

• The modulation process involves combining the baseband signal with the carrier wave to create a modulated signal. The choice of modulation technique determines how this combination occurs. There are several common modulation types:

  a. Amplitude Modulation (AM):

  • In AM, the amplitude of the carrier wave is varied in proportion to the amplitude of the baseband signal. When the baseband signal is at its peak, the carrier wave's amplitude is maximum, and vice versa. AM is commonly used in broadcast radio.

  b. Frequency Modulation (FM):

  • In FM, the frequency of the carrier wave is varied based on the amplitude of the baseband signal. As the baseband signal varies, the carrier wave's frequency changes accordingly. FM is used in FM radio broadcasting.

  c. Phase Modulation (PM):

  • In PM, the phase of the carrier wave is altered based on the baseband signal. Variations in the baseband signal lead to phase shifts in the carrier wave. PM is often used in some digital communication systems.

  d. Quadrature Amplitude Modulation (QAM):

  • QAM combines both amplitude and phase modulation. It uses a combination of amplitude changes and phase shifts to encode information. QAM is prevalent in digital communication systems, including Wi-Fi and cable television.

5. Transmission:

• The modulated signal, which now carries the information, is transmitted through a transmission medium, such as air for wireless communication or a cable for wired communication.

6. Demodulation:

• At the receiving end, the demodulation process is used to extract the original baseband signal from the received modulated signal. The demodulator reverses the modulation process, depending on the modulation type.

7. Recovery of Information:

• Once the baseband signal is demodulated, it is passed through a filter or decoder to recover the original information. For example, in audio communication, the baseband signal is sent to a speaker to produce sound.

Reasons why modulation is used

There are 2 things

• Baseband Signal - Data that needs to be transmitted
• Carrier Signal - Wave on which data will be sent

e.g. Conside the radio station where voice signal (Base band signal) is being transmitted. Without carrier signal, we will need huge antenna to send signal. Also the quality of signal will be low due to interference because voice signal has a frequency in the range of 3khz. Also entire audible spectrum is in the range of 20hz to 20khz! So it is not feasible to transmit such low frequency signals using baseband signal. That's why we use carrier waves to send the baseband signal by changing carrier wave properties like frequency, wavelength or phase.

Modulation types

• Analog - Baseband signal is in analog form
• Digital - Baseband signal is in digital form - 0 and 1

Analog Modulation

• Continuous wave modulation - AM (Amplitude of carrier wave is changed based on message signal) , FM (Frequency of carrier wave is changed based on message signal), PM (Phase of carrier wave is changed based on message signal)
• Pulse Modulation (Carrier signal is pulse signal) - PAM, PWM, PPM, PCM (Pulse Code)

Digital Modulation

• ASK - Amplitude shift keying - Amplitude of carrier wave is changed based on data signal (baseband signal)
• FSK - Frequency shift keying - Frequency of carrier wave is changed based on data signal (baseband signal)
• PSK - Phase shift keying - Phase of carrier wave is changed based on data signal (baseband signal)