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Frequency Modulation

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Frequency Modulation In telecommunications and signal processing , frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. In analog frequency modulation, such as FM radio broadcasting of an audio signal representing voice or music, the instantaneous frequency deviation , the difference between the frequency of the carrier and its center frequency, is proportional to the modulating signal. Waveform The frequency of a carrier (fc) will increase as the amplitude of modulating (input) signal increases. The carrier frequency will be maximum (fc max) when the input signal is at its peak. The carrier deviates maximum from its normal value. The frequency of a carrier will decrease as the amplitude of the modulating (input) signal decreases. The carrier frequency will be minimum (fc min) when the input signal is at its lowest. The carrier deviates minimum from its normal value. The frequency of the carrier will
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Phase Modulation

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Phase Modulation It is very similar to FM except that the phase of the carrier is varied and not the frequency. As the modulating signal goes positive, the amount of phase lag increases with an increase in the amplitude of the modulating signal. The effect is that the carrier signal is stretched or its frequency is reduced. When the modulating signal goes negative, the phase shift becomes leading. This causes the carrier to be compressed and hence the frequency increases. Thus phase modulation produces frequency modulation. The below fig.(a) shows the modulating signal fig.(b) shows FM and fig.(c) shows PM. PSK: Phase Shift Keying Comparison of AM, FM, PM                         FM                        AM 1. Amplitude of FM wave is constant. It is independent of the modulation index. Amplitude of AM wave will change with the modulating voltage. 2. Transmitted power remains constant and is independent of modulation index. Transmitted power is depend
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Amplitude Modulation

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Amplitude Modulation: In amplitude modulation the information is stored in the variation in amplitude of the signal. Modulation of a signal is done to reduce the noise and transmit the signal, and we demodulate the signal at the receiver. Modulating signal E m cos(w m t) Carrier signal E c cos(w c t) AM signal E c [1+mcos(w m t)]cos(w c t) Modulating index E c /E m Frequency UB f max =f c +f m Frequency LB f min =f c -f m Bandwidth  2f m Carrier power E c /2R Power in sideband m 2 P c /4 SSB – It is single side band. In this signal only one of the sidebands is present. DSB - It is the double sideband. The fig shown below is DSB. It we suppress its carrier the signal is called DSBSC that is double side band suppressed carrier   Amplitude modulator- Amplitude modulator is a device that modulates the signal there are two types of AM modulators low level and high level. Low level – The RF oscillator is stabilized in order
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Modulation

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Communication We convey our messages to other people through voice, facial expressions, gestures. These are the communication methods between people . These messages are often base-band audio, video and even digital bits from computers. Telecommunication is the core for sending messages from one place to another . Here, we are discussing various sorts of modulations which are used by telecommunication devices. Before we start this subject allow us to return to the history of telecommunication. Telephone was the primary device to send analog audio signals over long distance through copper wire. Telegraph was on the opposite was used to send messages within the sorts of dash-dots. Telephone and telegraph remains the base of all modern day's communication. These days we send audio, video, bit streams from computers through copper wires, co-axial cable, even through wireless radio waves, microwaves, infrared, and with visual lights through glass fiber . B
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