3

RF transmission lines

Transmission line operation at d.c.

In the later part of this chapter, how a transmission line behaves when conducting radio frequency signals will be discussed. But a useful insight into what happens when such a signal arrives at the end of a transmission line, and how it gets reflected, can be gained by considering a signal of frequency 0 Hz, i.e. the d.c. case. This also turns out to be an important consideration in some radio frequency equipments, namely radar transmitters, as will appear later. For simplicity, let’s assume the transmission line is in air, or even in vacuo, so that the velocity of propagation is nearly the speed of light, 300 mm per nanosecond1, that it has a ‘characteristic impedance’ of 300O and ...

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