Transistor Oscillator for Use in Multifrequency Pulsing Current Supply

A large proportion of the telephone calls made require connections to be set lip in more than one central office. AVhere common control systems are used, this requires that information needed by the second central office be transmitted to it from the first central office which in turn has received its information from the calling subscriber. The "language" used in some cases for transmitting the information is in the form of short pulses of alternating current. Each pulse consists of a combination of two of six available frequencies. Twelve combinations of the six frequencies make up the total "vocabulary". Ten are required for digits and two for special signals sent at the beginning and end of pulsing. This is known as multifrequency, M F , pulsing. The device which controls the pulses is called an MF sender. The device which receives the MF pulses and translates the information received for use by other equipment is called an MF receiver. An operator may also use multifrequency pulsing when transmitting information by means of a key set to a distant office. Control of the frequencies used is obtained by contacts on the key depressed. Twelve keys are used. The previous source of ac was a circuit capable of supplying both operator positions and senders. This equipment is however quite expensive. If only a few senders in an office require the MF current the cost per 1313