The pseudo-noise (or pseudo random) sequence is a noise like high frequency signal. This signal is binary in nature. Thus it looks like pulses. The sequence is not completely random but it is generated by a well defined logic. The same logic is used at transmitter and receiver. Since the sequence is generated by a
Generation of Pseudo-Noise (PN) Sequences Read More »
Necessity of Secure Communication There are some applications where it is necessary for the system to resist external interference and to make it difficult for unauthorized receivers to receive the message being transmitted. This type of communication is called secure communication such that noise interference and unwanted receivers should not detect the message. Such communication
Spread Spectrum (SS) Techniques – Pedagogy Zone Read More »
A convolutional coding is done by combining the fixed number of input bits. The input bits are stored in the fixed length shift register and they are combined with the help of mod-2 adders. This operation is equivalent to binary convolution and hence it is called convolutional coding. This concept is illustrated with the help
Definition of Convolutional Coding – Pedagogy Zone Read More »
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
Line Coding in Communication Engineering – Pedagogy Zone Read More »
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
Adaptive Delta Modulation (ADM) – Pedagogy Zone Read More »
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
Concepts of Sampling and Sampling Theorems Read More »
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
Automatic Frequency Correction (AFC) Read More »
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
Frequency Modulation Using Varactor Diode Read More »
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
Comparison Between Amplitude Modulation and Angle Modulation Read More »
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
Performance Parameters of Radio Receiver Read More »