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Communication is the transmission of information. The transmitter, channel and receiver are the three essential parts of any communication system. There are two basic modes of communication: point to point and broadcast.
Radios and television are examples of broadcast communication systems in which there are many receivers in correspondence to a single transmitter.
Frequency modulation (FM) is a process in which the frequency of the carrier wave is changed following the message signal. The carrier amplitude remains constant in frequency modulation while the carrier frequency varies.
Modulation and its necessity
Original low-frequency information cannot be transmitted for long distances due to various reasons; therefore, at the transmitter, the low-frequency signals are superimposed on a high-frequency wave that acts as a carrier for the information; this process is known as modulation.
The use of a communication system is to transmit information. This information on message signals is also known as baseband signals. They essentially represent the band of frequency representing the original signal. Remember that no signal is a single frequency sinusoid, but it spreads over a range of frequencies called the single bandwidth.
Types of modulation
The information signal can control three factors: amplitude, angular frequency, and the carrier wave’s initial phase, resulting in the three modulation types during the modulation process.
- Amplitude modulation (AM):
Amplitude modulation is the process of encoding information on a particular signal by varying the amplitude.
- Frequency modulation (FM) :
Frequency modulation is a process of encoding information on a particular signal by varying the carrier wave frequency of the modulating signal.
- Phase modulation (PM):
Phase modulation is the process of encoding information on a particular signal by varying the instantaneous phase of a career wave.
Frequency modulation index
The frequency modulation index is the ratio of frequency deviation to the modulating frequency.
Modulation index(M) = frequency deviation/modulating frequency
M = Δffm
Where ∆f is frequency deviation and fm is modulating frequency.
Frequency modulation and its type
- Narrow-band frequency modulation is a condition where the modulation index is small. The maximum modulation frequency is 3kHz, and the maximum frequency deviation is 75kHz.
- Wide-band frequency modulation is defined as a condition where the modulation index is larger. Modulation frequency ranges from 30Hz to 15kHz, and the minimum deviation is 75kHz.
Frequency modulators
Voltage-controlled oscillator – used to form direct frequency modulation by directly giving the message into the input of the oscillator.
Crystal oscillator single – in this, a varactor diode is used in a crystal oscillator circuit, where signals need to be multiplied in frequency and only narrow-band frequency modulation is achieved.
Phase-locked loop – this is used to detect the phases and frequency of the carrier components of a frequency modulation signal.
Importance of frequency modulation
- The amplitude of the frequency-modulated wave does not get affected.
- Frequency modulation decreases the noise; hence there is a significant increase in signal-to-noise ratio.
- We can also reduce the noise by increasing the frequency deviation.
- It also reduces the interference by the adjacent channels through guard bands
- It operates in a very high frequency called VHF
- It is resistant to single strength variations
- It does not require a linear amplifier in the transmitter
Disadvantages of frequency modulation
- FM cannot cover large areas.
- The transmitting and receiving equipment of FM is complex and expensive.
- Generally, wider channels of 200kHz are required for FM.
- The antennas for FM need to be closely placed for better signals.
Applications of frequency modulation
FM radio and music: Frequency modulation is widely used in radio broadcasting. It is a wideband FM, and its frequency is much larger than that of AM. Due to its low radio frequency interference, it is preferred to use FM to broadcast music on the radio.
Television sound: The video information in a television broadcast is transmitted using AM, while FM is used for sound transmission due to low interference.
Satellite TV: Some satellites use FM to broadcast video signals on the receiver’s station.
Conclusion
Communication systems play a significant role in our daily lives. Frequency modulation is a type of modulation where frequency and phase remain constant. Frequency modulation is the process by which the frequency of the carrier signal changes with respect to the modulating frequency.
It is broadly used in national radio broadcasts, satellite TV, TV, sound, music and video transmission instruments. It has various advantages over amplitude modulation and phase modulation. It provides noise immunity better than AM and PM. It offers low interference and a high sound-to-noise ratio.
