![]() ![]() Navy uses these frequencies for submarine communications.ġ-1 The electromagnetic spectrum from VLF to X-ray. The extremely low frequency (ELF) range includes ac power-line frequencies as well as other low frequencies in the 25- to 100-hertz (Hz) region. The spectrum extends from the very lowest ac frequencies and continues well past visible light frequencies into the X-ray and gammaray region. 1-1) is broken into bands for the sake of convenience and identification. Any use is subject to the Terms of Use as given at the website.Ģ Introduction to RF electronics The electromagnetic spectrum (Fig. 1 Downloaded from Digital Engineering Library McGraw-Hill (Copyright © 2004 The McGraw-Hill Companies. Before proceeding with RF electronic circuits, therefore, take a look at the electromagnetic spectrum. The electromagnetic spectrum When an RF electrical signal radiates, it becomes an electromagnetic wave that includes not only radio signals, but also infrared, visible light, ultraviolet light, X-rays, gamma rays, and others. ![]() Interference and other strange effects are found at RF that are missing in dc circuits and are negligible in most lowfrequency ac circuits. Thus, coupling effects between elements of the circuit, between the circuit and its environment, and from the environment to the circuit become a lot more critical at RF. Another problem with RF circuits is that the signals find it easier to radiate both from the circuit and within the circuit. As frequency increases, skin effect produces a smaller zone of conduction and a correspondingly higher value of ac resistance compared with dc resistance. The term skin effect refers to the fact that ac flows only on the outside portion of the conductor, while dc flows through the entire conductor. In some older very high frequency (VHF) TV tuners and VHF communications receiver front ends, the stray capacitances were sufficiently large to tune the circuits, so no actual discrete tuning capacitors were needed. These stray parameters are not usually important at dc and low ac frequencies, but as the frequency increases, they become a much larger proportion of the total. Stray inductance is the normal inductance of the conductors that connect components, as well as internal component inductances. Stray capacitance is the capacitance that exists between conductors of the circuit, between conductors or components and ground, or between components. Stray capacitance and stray inductance afflict these circuits. Introduction to RF electronics Radio-frequency (RF) electronics differ from other electronics because the higher frequencies make some circuit operation a little hard to understand.
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