Electronics and Telecommunications: Frequency modulation
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This document discusses various digital modulation techniques including frequency modulation (FM), amplitude modulation (AM), phase modulation, pulse code modulation (PCM), pulse amplitude modulation (PAM), pulse time modulation, pulse position modulation, and multiplexing. It defines these terms and concepts, explains how they work, compares AM and FM, and discusses bandwidth and noise considerations for FM.
Electronics and Telecommunications: Frequency modulation
- 1. U N I T V FREQUENCY MODULATION
- 2. DEFINATION OF FREQUENCY MLODULATION (FM) • Frequency modulation (FM) is a method of impressing data onto an alternating-current (AC) wave by varying the instantaneous frequency of the wave. • Frequency modulation is similar in practice to phase modulation (PM). When the instantaneous frequency of a carrier is varied, the instantaneous phase changes as well.
- 4. DIFFERENCE OF AM AND FM (a) Carrier wave. (b) Sinusoidal modulating signal. (c) Amplitude- modulated signal. (d) Frequency- modulated signal.
- 5. CONCEPT OF BANDWIDTH • In electronic communication, bandwidth is the range of frequencies that an electronic signal uses on a given transmission medium. • This range is also referred to as the band and bandwidth literally describes the difference between the highest-frequency signal component and the lowest- frequency signal component. • Since the frequency of a signal is measured in hertz (the number of cycles of change per second), a given bandwidth is the difference in hertz between the highest frequency the signal uses and the lowest frequency it uses.
- 6. FREQUENCY MODULATION BANDWIDTH • In the case of an amplitude modulated signal the bandwidth required is twice the maximum frequency of the modulation. • As a frequency modulated signal has sidebands that extend out to infinity, it is normal accepted practice to determine the bandwidth as that which contains approximately 98% of the signal power. • A rule of thumb, often termed Carson's Rule states that 98% of the signal power is contained within a bandwidth equal to the deviation frequency, plus the modulation frequency doubled, i.e.:
- 7. NOISE TRINGLE • Noise triangle is a triangular noise distribution for FM. • Noise triangle is the study of effect of noise on the carrier signal of the FM wave.
- 9. PHASE MODULATION phase modulation, PM, is used in many applications to carry both analogue and digital signals. Keeping the amplitude of the signal constant, the phase is varied to carry the required information or signal.
- 10. PULSE CODE MODULATION (PCM) • Pulse code modulation (PCM) is a digital scheme for transmitting analog data. • The signals in PCM are binary; that is, there are only two possible states, represented by logic 1 (high) and logic 0 (low). • Using PCM, it is possible to digitize all forms of analog data, including full-motion video, voices, music. • To obtain PCM from an analog waveform at the source (transmitter end) of a communications circuit, the analog signal amplitude is sampled (measured) at regular time intervals.
- 11. PULSE CODE MODULATION (PCM)
- 12. SAMPLING METHOD • In signal processing, sampling is the reduction of a continuous signal to a discrete signal. A common example is the conversion of a sound wave (a continuous signal) to a sequence of samples (a discrete-time signal). • A sample refers to a value or set of values at a point in time and/or space. • A sampler is a subsystem or operation that extracts samples from a continuous signal. • A theoretical ideal sampler produces samples equivalent to the instantaneous value of the continuous signal at the desired points.
- 13. SAMPLING THEOREM
- 14. PULSE AMPLITUDE MODULATION • Pulse amplitude modulation (PAM) is the transmission of data by varying the amplitude s ( voltage or power levels) of the individual pulses in a regularly timed sequence of electrical or electromagnetic pulses. • PAM is only one of several forms of pulse modulation. Other methods include varying the durations (or widths), the frequencies, the positions, or the intervals of the individual pulses in a sequence.
- 15. PULSE TIME MODULATION • Time characteristics of pulses may also be modulated with intelligence information. • Two time characteristics may be affected: • (1) the time duration of the pulses, referred to as PULSE-DURATION MODULATION (PDM) or PULSE-WIDTH MODULATION (PWM)
- 16. PULSE POSITION MODULATION • The amplitude and width of the pulse is kept constant in the system. The position of each pulse, in relation to the position of a recurrent reference pulse, is varied by each instantaneous sampled value of the modulating wave.
- 17. MULTIPLEXING • Multiplexing is sending multiple signals or streams of information on a carrier at the same time in the form of a single, complex signal and then recovering the separate signals at the receiving end. • In analog transmission, signals are commonly multiplexed using frequency-division multiplexing (FDM), in which the carrier bandwidth is divided into sub-channels of different frequency widths, each carrying a signal at the same time in parallel. • In digital transmission, signals are commonly multiplexed using time-division multiplexing (TDM), in which the multiple signals are carried over the same channel in alternating time slots.
- 18. MULTIPLEXING
- 19. MULTIPLEXING