Telephone transformers

Wm. Fondiller: Mr. Casper has described the ideal transformer, one which would introduce zero loss in a telephone circuit, as represented by an equivalent network having zero impedance series arms and an infinite impedance shunt arm. In any practical transformer the factor which most largely determines the extent to which this ideal can be approached is the magnetic material used for t he core. The ideal core material obviously would be one having infinite permeability and zero losses, as this would make possible 100 per cent coupling, practically zero winding resistance and infinite mutual impedance. Fortunately, however, a magnetic material having characteristics altogether finite in value will permit the construction of quite satisfactory transformers. It may be of interest to indicate what the desirable properties of the magnetic material should be and the extent to which they are attained in materials at present commercially available.