# Quiz 14: Transmission Lines

Transmission line is a line, which helps in transmitting signals from transmitter to receiver or vice versa, with the help of antenna. There are number of ways in which signal can proceed from transmitter to receiver, which includes metallic cable, radio transmission and metallic cable. Transmission line consists of conductors and this combination of conductors has all of them, that is, resistance, inductance and capacitance. Now to understand the transmission line, consider the short section of the transmission line and then draw the equivalent circuit of it. Draw the equivalent circuit of the balanced transmission line. Draw the equivalent circuit of the unbalanced transmission line. Figure 1 consists of length of line, which is much smaller than a meter. The transmission line consist of resistance of the wire, that is, R and the conductance of the dielectric, that is, G and the shunt capacitance, that is, C and the series inductance, that is, L. To understand the figure, both low and high frequencies will be considered. Now at low frequencies, shunt capacitive reactance is very large, due to which effect of the capacitance is very small and can be ignored. Similarly, Inductive reactance is very small, as compare to the reactance of the line and can be neglected. So, at low frequency the transmission line can be characterized by its resistance and by the conductance of the dielectric, which can be neglected. Now as the frequency increases the inductance and capacitance start having its effect. Therefore, at high frequency, the series inductive reactance is very large and parallel capacitive reactance is very low. In fact, at high frequency, resistance of line can ignored and line can be considered purely of inductance and capacitance.