ly wound to produce maximum energy (Zo) is used to feed a transmission (TX) line with transfer by magnetic coupling. Coil windings are designed a characteristic impedance Z. The output of the line is to have minimum self-capacitance, minimum inter-winding fed to a number (n) of receivers, each of which is as- capacitance and minimum capacity coupling between each sumed to have an input impedance (Zin) equal to Zo. winding and earth. No direct connection is used between Resistors R represent the matching network resistors input and output circuits. The above conditions are neces- which must be evaluated to ensure properly terminated sary, otherwise balanced circuits will become unbalanced conditions. when parts of the circuit are connected together. The For the system to be properly terminated, it is es- balanced/unbalanced transformer is bi-directional; it can be sential that the aerial and cable system be terminated used to pass energy in either direction. with Zo, i.e. the impedance to the fight of the plane 'AE' As the operational frequencies become higher and must present an impedance Zo to the antenna and cable higher (above 2 GHz), it becomes increasingly difficult to system. It is also essential that each receiver be energised make such a good transformer and a transformer is simply from a source impedance (Zs) matched to its own input not used and antennas and transmission lines are connected impedance (Zin), i.e. Zs = Zin. For ease of analysis we will directly. In such cases, the systems resolve to either an assume the practical case, Zs = Zin = Zo. unbalanced antenna and distribution system or a balanced Now for the transmission line in Figure 2.1-23 to be antenna and distribution system. The unbalanced system is properly terminated: almost always used because of convenience and costs. R+[R + Zol/n = Z 2.1.7.2 Multi-point antenna distribution systems Multiplying both sides by n: In the design of antenna distribution systems, trans- nZ = nR + R + Z mission lines connecting signal distribution points must