Universal Winding Transformer

In carrier frequency transmitters, transformers are normally used for coupling between stages and for coupling the output stage to the line. They sometimes transform a large amount of carrier power. Coils are usually wound in single layers, spaced well apart to reduce capacitance, and have but few turns. If the necessary turns cannot be wound in a single layer, a bank winding like that shown in below Fig. may be used.

This winding has more capacitance than a single layer but much less than two layers wound in the ordinary way. Since intrawinding layer-to-layer capacitance is zero in these transformers, the resonance frequency f_r is usually determined by winding-to-winding capacitance.

High, narrow core windows or several pies are desirable to reduce leakage inductance. Transformer loss is mostly core loss. Two-mil grain-oriented steel can be used advantageously in such transformers, because of its low losses and high permeability. In transmitter operation, class AB or class B amplifiers are commonly used, with or without modulation, which may be as high as 100 per cent. In a receiver, input and interstage transformers also are employed, mainly to obtain voltage gain or for isolation purposes. Similar transformers are used for line matching, especially where overhead lines are connected to underground cables. Line impedance changes abruptly, and transformers may be necessary for good power transfer.