Design of filters for carrier programme circuits

The important advantages over other types of circuit of a carrier telephone system of the single side-band suppressed-carrier type for meeting the increasing demand for high-quality programme circuits are outlined. In such a carrier system the necessity of suppressing the unwanted side-band to a sufficiently great extent is explained, as is also the difficulty of obtaining the desired degree of suppression in a system transmitting very low voice frequencies; and the application of quartz crystals to assist in obtaining the necessary side-band suppression is described. Typical frequency-loss curves are given, showing experimentally, with a crystal used in the manner described, the effects of capacities in series and in parallel with the crystal