The analog waveforms are converted to digital signals by PCM, DM, ADM, DPCM etc. techniques. This digital data can be represented by different formats or waveforms. These waveforms are commonly known as digital data formats or their representation is called as line coding. Digital symbols can amplitude modulate some carrier to generate amplitude modulated pulse
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To overcome the quantization errors due to slope overload and granular noise, the step size (δ) is made adaptive to variations in the input signal x(t). Particularly in the steep segment of the signal x(t), the step size is increased. When the input is varying slowly, the step size is reduced. Then the method is
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The first operation in digital communications is the sampling. Almost all the natural signals exist in analog form. For example, voice, any moving scene, environmental data etc. exist in analog or continuous form. Such information can be transmitted from one place to another by continuous modulation of the suitable carrier. Then this type of communication
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The automatic frequency correction (AFC) is incorporated in FM transmitter to keep carrier frequency stable. The discriminator reacts only to small changes in the carrier frequency but not to the frequency deviations in the carrier (since it is too fast). Suppose frequency of the carrier increases. This higher frequency is fed to the mixer for
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All the diodes exhibit small junction capacitance in the reverse biased condition. The varactor diodes are specially designed to optimize this characteristic. The junction capacitance of the varactor diode changes as the reverse bias across it is varied. The variations in capacitance of this diose are aide and linear. The varactor diodes provide the junction
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Angle modulation has following advantages over amplitude modulation (AM): The amplitude of FM is constant. It is independent of depth of modulation. Hence transmitter power remains constant in FM whereas in FM it varies in AM. Since amplitude of FM is constant, the noise interference is minimum in FM. Any noise superimposing an amplitude can
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The performance of a radio receiver is measured on the basis of its selectivity, sensitivity, fidelity and image frequency rejection. Selectivity The selectivity is the ability of the receiver to select a signal of a desired frequency while rejecting all others. The selectivity of the receiver is obtained partially by RF amplifier and mainly
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The problems of TRF receiver are overcome in this receiver. The superheterodyne receiver converts all incomming RF frequencies to a fixed lower frequency, called Intermediate Frequency (IF). This IF is then amplified and detected to get the original signal. Fig shows the block diagram of superheterodyne receiver. The antenna receives all the frequency signals and
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Fig shows the block diagram of Tuned Radio Frequency TRF receiver. The received signal is weak and noisy. It is given to broadband RF amplifier. The RF amplifier enhances signal to noise ratio and amplifies the signal. It is then passed through AM detector. The output of AM detector is audio signal. The detected
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3Φ AC synchronous motor Revolving armature type Revolving field type Conventional 3Φ Synchronous Motor : (Revolving Field Type) Stator : Stator is made up of silicon steel stampings. Stator slots carry a balanced 3Φ armature winding, wound for a specified even number of poles. The ends of the armature windings are connected to the terminals
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