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Showing posts from September, 2010

Current

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Current is moving charge, typically electrons. And just as the amount of water flowing in a river can be measured, so can the amount of flowing electrons through a medium. To make this measurement, we simply pick a reference point and count the number of electrons that flow past that point over time. The standard measure of electrical current is the Ampere, often referred to just as “amp”. It is equal to 6.24e18 (that’s 6 quintillion!) electrons flowing past a reference point in 1 second. The amp is named after André-Marie Ampère, a French physicist credited with the discovery of electromagnetism. Many times the term amp is abbreviated as just a capital A. For example, instead of seeing “5 amps” it may be more common to see “5A". This is especially true when SI prefixes are used, such as writing 5mA instead of 5 milliamps. Finally, the terminology of current is often abbreviated with the letter I (probably because the letter C had already been used as an abbreviation for charge).

CHEBYSHEV FILTERS

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Chebyshev filters are used to separate one band of frequencies from another. Although they cannot match the performance of the windowed-sinc filter, they are more than adequate for many applications. The primary attribute of Chebyshev filters is their speed, typically more than an order of magnitude faster than the windowed-sinc. This is because they are carried out by recursion rather than convolution. The design of these filters is based on a mathematical technique called the z-transform . Chebyshev filters have the property that they minimize the error between the idealized filter characteristic and the actual over the range of the filter, but with ripples in the passband. This type of filter is named in honor of Pafnuty Chebyshev because their mathematical characteristics are derived from Chebyshev polynomials . Type I Chebyshev filters

Filters

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1.1     Introduction The function of a filter is to remove unwanted parts of the signal (such as random noise) or to extract useful parts of the signal (such as the components lying within a certain frequency range). There are two main kinds of filter: analog and digital. They are quite different in their physical makeup and in how they work. An analog filter uses analog electronic circuits made up from components such as resistors, capacitors and op-amps to produce the required filtering effect, whereas a digital filter uses a digital processor to perform numerical calculations on sampled values of the signal. The processor may be a general-purpose computer such as a PC, or a specialized DSP (Digital Signal Processor) chip. Microwave filters represent a class of electronic filter, designed to operate on signals in the megahertz to gigahertz frequency ranges (medium frequency to extremely high frequency). This frequency range is the range used by most broadcast radio, television, wire