Category: Telecommunication Systems
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Microwave Active Devices: Types, Features & Operation
Generally microwave devices can be categorized as either passive components or active components. We have already talked about microwave passive components in this other article. This article focuses on microwave active devices. They may be classified into two types: low-power solid-state devices and high-power vacuum tube devices. Communications involving the gigahertz bandwidths cannot employ conventional…
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Microwave Passive Components: Types & Functions
The part of the electromagnetic spectrum referred to as the microwave region loosely includes 1-300 GHz for practical purposes. These microwave bands are especially advantageous for transmission services such as satellite transmission, telephone transmission, broadcasting of commercial radio & television, and oil platform transmission. Some of the key advantages of microwaves are that the energy…
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Frequency Synthesizer – Features, Operation & Applications
Frequency synthesis is a technique of producing a range of frequencies with crystal-controlled stability. A frequency synthesizer uses phase-locked loop (PLL) to generate output frequencies over a wide range. The typical range is from 1 MHz to 160 MHz. As illustrated in the block diagram above, the key components of the frequency synthesizer are: The…
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Phase-Locked Loops (PLL) – Features, Operation & Applications
Features of a Phase-Locked Loop (PLL) A phase-locked loop (PLL) is a form of a servo system which consists of a phase detector, low-pass filter and voltage controlled-oscillator (VCO) as illustrated in the block diagram below. The phase detector compares the phase of the VCO with the incoming reference signal, giving an output proportional to…
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Radio Frequency (RF) Signal Generator – Features & Applications
A radio frequency (RF) signal generator is used in generating high frequency signals at a specific frequency for testing laboratories. The output frequency may range for example from about 100 kHz to around 40 GHz. A typical RG generator consists of: RF oscillator, amplifier, output level meter and a calibrated attenuator. Components of RF Generator…
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Diode & Filter Applications in Amplitude Modulation (AM) Detection Circuits
The operation of a typical AM audio frequency signal is illustrated in the Figure 1.0 where vin is the modulated signal that is shown Figure 1.1. A typical amplitude modulated signal that is fed into the detector circuit: The diode removes the lower envelope and the upper envelope is illustrated below: The capacitor C2 and…
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Open Systems Interconnection Communication (OSI) Model
Developed by the ISO (International Organization for Standards) in 1983, the Open Systems Interconnection (OSI) reference model divides communication functions into seven-layer standard protocol system. The OSI model is a framework for developing a coordinated system of standards. The seven layers are described as follows: 1 Physical Layer This layer describes the means for bit…
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How Cellular Communication Systems Works
In cellular communication systems, there is a two-way wireless transmission between the cellular phone handset and the base station tower. The cell phone converts the audio signals into electrical form using a microphone. This information is imposed on a high frequency carrier signal by the process of modulation. The modulated carrier is radiated into free…
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Features of Optical Modulators in Telecommunication Systems
Light emitting PN junction devices such as LEDs and laser diodes are easily modulated by superimposing signals on to the injected current. This is direct modulation. Laser diodes in high-bit rate and long-span optical communication systems are often used under direct modulation. The downside of direct modulation is that, it results in chirping which limits…
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Network Access Control Techniques
Access control methods are required in a network to ensure that only one user of the network is able to transmit at any one time. In ring-based local area networks (LANs), two commonly employed techniques are: Token Passing In this technique, a token i.e. a special bit pattern, is circulated. When a station wishes to…