Composite telegraphy and telephony on open wire lines

The paper describes the well-known method of superposing two telegraph channels on a telephone loop circuit. The maximum trustworthy telegraph speed obtainable on such circuits is given as 25 cycles, and at this speed the numbers of six-letter words transmitted by various telegraph systems are given below: Wheatstone60 words per minuteStart-stop60 words per minuteBaudot88 words per minuteFive-unit multiplex90 words per minute Either close-circuit (single-current) or double-current working may be adopted. Telegraph currents should not exceed 60 to 65 milliamperes. Telephone ringing is effected with 135-cycle ringing equipment. The decrease in telephone transmission efficiency is dependent on the type of circuit and the composite apparatus. On non-loaded circuits with terminal composite sets only the loss is of the order of 1 T.U. The composite ringer causes a transmission loss of 0.1 T.U. The transmission loss on loaded circuits is considerably less than on non-loaded and may be as low as 0.1 T.U. Using composite methods, the first cost is less than 8% and the annual charges 13% of the expenditure involved in the provision of a 2-mm. diameter copper conductor for furnishing identical facilities.