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Communication System is a group of individual telecommunication networks, transmission systems, tributary stations, relay stations, and terminal equipment usually capable of interconnection and interoperation to form an integrated whole.
Modulation is a process by which information is encoded from a message source to optimise it for transmission. Frequency modulation is the coding of information in a career wave by changing the waves’ instantaneous frequency. Frequency modulation technology is commonly used in computing, telecommunication, and signal processing.
Frequency modulation
Frequency modulation is a modulation in which the frequency of the carrier wave is altered for the instantaneous amplitude of the modulating signal, the phase of the carrier wave and the amplitude is kept constant.
The purpose of modulation of the frequency of carrier waves is to send information over small distances.
Frequency modulation in a communication system
Two types of frequency modulation are used in the communication system. These are analogue frequency modulation and digital frequency modulation.
In Analogue modulation, a continuous varying sine carrier wave modulates the data signal. The significant three defining properties of a carrier wave is frequency amplitude and phase. These properties are used to create AM, PM, and FM.
Digital Modulation is similar to analogue modulation, and it is categorised into frequency shift key, amplitude shift key, or face shift key. The analogue modulation is used for AM, FM and shortwave broadcasting, while digital modulation involves the transmission of binary signals.
Graphical representation of frequency modulated wave
There are two waves; the initial wave is the message signal which holds the information.
The second wave is a signal with no data known as the carrier signal.
The modulation of these two waves results in the formation of the frequency modulated waves.
The FM modulated wave is sensitive as its frequency moves up and down depending on the amplitude of the message signal.
The change frequency is represented in the form of kilohertz.
Representation of frequency modulation
The modulating signal (input signal) is represented as
i(t) = β.sin (2𝜋fit)
The carrier signal is represented as
c(t) = Ac cos(2𝜋fct)
Ac represents the amplitudes of the carrier signal, and fi and fc are the frequencies of the two waves correspondingly.
the modulated wave is represented as
F(t) = Ac. cos [2𝜋fct + β.sin (2𝜋fit)]
And β represents the modulation index of the frequency-modulated wave.
FM Modulation index
The modulation index of FM is defined as the ratio of the maximum carrier frequency to the modulating signal frequency.
The symbol β denotes it.
The equation is given as
β = ∆f/fi
FM bandwidth
It is defined as the total range of frequency required to pass a specific signal that has been modulated to carry data without the distortion or loss of the data.
Constant bandwidth system in FM
Frequency modulation is considered a constant band with the system for the following reasons.
The amplitude of a frequency modulated wave always remains constant.
The power of a transmitted signal all through the transmission stays constant.
The bandwidth is not increased and remains constant unless the modulation frequency increases.
Frequency modulators
The FM signals are generated through various approaches via frequency modulators.
There are various types of frequency modulators.
Varactor diode oscillator- The FM signal is generated by placing a varactor diode in the tuned circuit of the oscillator circuit. Minimum frequency is observed in the Modulator signals. To achieve narrowband FM signals, they need to be amplified.
Phase-locked loop- FM signals are best generated by this method. All it is necessary to handle the constraints present in the loop precisely.
Difference between AM and FM
In FM says an amplitude stays as constant while in AM phase and frequency remains constant
FM modulated signals are more affected than AM modulated signals
The modulation index is always more than 1 in FM while it ranges between 0-1 in AM
FM signals are less affected with interference and distortion as compared to AM signals
FM signals are used for short distances, while am signals are preferred for large distances
Applications of frequency modulation
Frequency modulation is used in various fields that include
Seismic prospecting
Magnetic Tape recording
Radar transmissions
Radio broadcasting
Telemetry
Music synthesis
Observation of EEG signals
Conclusion
Frequency modulation plays a vital role in communication systems: the mathematical representation of frequency modulation wave consists of a sinus, the expression with the integral of the baseband signal added to the argument of sin or cosine function.
The modulation index is used to make the frequency division more sensitive or less sensitive according to the variation in the baseband value.
The modulation index and the ratio of the modulating signal amplitude to the modulating signal’s frequency influence the frequency modulated spectrum.
