Quiz 14: Transmission Lines

Trade & Technology

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. Extension cord is an electrical cable which has one or more sockets at one end while plug at the other end. It comes in several colors, lengths and thickness. Television antenna cable helps in transmission of signals between the antenna and television. Now a day's, the coaxial cables are used for this purpose because it has low power losses and has larger insulating dielectric as compare to Extension cords. The reason why an ordinary extension cord is not considered as the transmission line, while a television antenna cable of same length would be because of the resistance offered by the ordinary extension cord. Now, the extension cord is also made up of conductor, and this conductor has resistance. Due to which the voltage at the load is lower than at the source. Therefore, it is not beneficial to use extension cord to run the load, as the load may operate very slowly and it may eventually burn out due to overheating. Therefore, it is always advisable not to use extension cord as the transmission line.

The differences between the balanced line and unbalanced line are done on the basis of the parameters listed below: The differences based on construction are, Balanced line: Two parallel conductors are used for construction of balanced line and the space between these two conductors varies from ½ inch to several inches. Unbalanced line: Coaxial cable is an example of unbalanced line, which is constructed by solid center conductor surrounded by the plastic insulator. This plastic insulator is surrounded by the conductor made up of fine wires braid shield. Then there is plastic cover, which acts at the outer cover. The differences based on characteristics are, Balanced line: In balanced line, with reference to ground, same amount of current flow in each wire. The flow of current in both the wires is equal in magnitude but opposite in direction. Unbalanced line: In unbalanced line, there is lack of symmetry with respect to ground. That is, for example, in coaxial cable, the flow of current in conductor is with reference to fine wire Braid shield and normally the conductor is placed outside is grounded. The differences based on suitable distance are, Balanced line: To protect against noise the balanced cable can be used for longer runs, that is, 15 to 30 meters. Unbalanced line: The unbalanced line is not able to suppress noise when there is interference from outside, so it is practically used for distance, which varies from 4-6 meters. The example of a balanced line is an open wire. The example of an unbalanced line is a coaxial cable.

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. img Draw the equivalent circuit of the unbalanced transmission line. img 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.

There is no answer for this question

There is no answer for this question

There is no answer for this question