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Introduction to RF
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 Radio-frequency (RF) electronics differ from other electronics because the higher
 frequencies make some circuit operation a little hard to understand. Stray
 capacitance and stray inductance afflict these circuits. Stray capacitance is the
 capacitance that exists between conductors of the circuit, between conductors or
 components and ground, or between components. Stray inductance is the normal inductance
 of the conductors that connect components, as well as internal component
 inductances. 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. 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.
 Also, skin effect exists at RF. 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.
 As frequency increases, skin effect produces a smaller zone of conduction
 and a correspondingly higher value of ac resistance compared with dc resistance.
 Another problem with RF circuits is that the signals find it easier to radiate both
 from the circuit and within the circuit. 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. Interference and other strange effects
 are found at RF that are missing in dc circuits and are negligible in most lowfrequency
 ac circuits.
 The electromagnetic spectrum
 
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