A Magnetic Amplifier for Radio Telephony

A magnetic amplifying device is described for permitting the control of radio frequency currents by varying the saturation of the iron core of an inductance included in the radio frequency circuit. The arrangement of windings of the amplifier is such that the controlling winding has no radio frequency E. M. F. induced in it, nor does it induce currents in the radio frequency coils. Various arrangements of this amplifier in connection with a solid steel rotor, radio frequency alternator are shown, notably those in series with the alternator and those in parallel. "Short-circuiting" condensers are connected to each of the radio frequency coils. A shunt condenser across both coils and their "short-circuiting" condensers increases the sensitiveness for reasons which are given. Another condenser inserted in series with the entire amplifier is employed to obtain linear proportionality of amplification and increased sensitiveness. The ratio of amplification is found to be proportional to the ratio of the frequency of the radio current to that of the controlling current. The control of the output of a 75 K. W. alternator of radio frequency for telephonic purposes is then shown by oscillograms to be accurate, and the numerical characteristics of alternator and amplifier separately and in combination are given.