## Production of Amplitude Modulated Wave – Class 12 | Chapter – 15 | Physics Short Notes Series PDF for NEET & JEE

Production of Amplitude Modulated Wave: An amplitude modulated wave is a type of signal that is produced by varying the amplitude of a high frequency carrier wave with a lower frequency modulating signal. The resulting AM wave contains the carrier wave, the modulating signal, and two sidebands that are created by the modulation process.

The amplitude modulated wave can be expressed mathematically as:

s(t) = (Ac + Am cos(2πfmt)) cos(2πfct)

where:

• s(t) is the amplitude modulated wave signal
• Ac is the amplitude of the carrier wave
• Am is the amplitude of the modulating signal
• fmt is the frequency of the modulating signal
• fct is the frequency of the carrier wave

The two sidebands are located at frequencies that are equal to the sum and difference of the carrier frequency and the modulating frequency. The upper sideband (USB) is located at a frequency of fct + fmt, while the lower sideband (LSB) is located at a frequency of fct – fmt. The carrier wave is located at a frequency of fct.

The bandwidth of an amplitude modulated wave is twice the frequency of the modulating signal, as it contains both the upper and lower sidebands. Therefore, AM waves require more bandwidth than the original modulating signal.

## Production of Amplitude Modulated Wave

The production of an amplitude modulated wave involves modulating a high frequency carrier wave with a low frequency audio or baseband signal. Here are the steps involved in the production of an AM wave:

• Generate the carrier wave: A high frequency sinusoidal wave is generated using an oscillator circuit. The frequency of the carrier wave is typically in the range of several hundred kilohertz to several megahertz.
• Generate the modulating signal: A low frequency audio signal or baseband signal is generated using a microphone or other audio input device. The audio signal is typically in the range of 20 Hz to 20 kHz.
• Modulate the carrier wave: The modulating signal is then mixed with the carrier wave using an AM modulator circuit. The modulator circuit varies the amplitude of the carrier wave in response to the amplitude of the modulating signal. This results in an AM wave that contains the original carrier wave and the modulating signal.
• Amplify the AM wave: The AM wave is then amplified using a power amplifier circuit to increase its power to the desired level.
• Transmit the AM wave: The AM wave is then transmitted using an antenna, where it propagates through space as an electromagnetic wave.
• Receive and demodulate the AM wave: The AM wave is received by a receiver, where it is demodulated to recover the original modulating signal. This is typically done using an envelope detector circuit, which removes the carrier wave and extracts the modulating signal.

The resulting demodulated signal is a replica of the original audio or baseband signal that was used to modulate the carrier wave. The demodulated signal can be amplified and played through a speaker or other audio output device to produce sound.

## Uses of Amplitude Modulated Wave

Amplitude Modulated (AM) waves have several uses in communication and broadcasting systems, including: