Page:EB1922 - Volume 32.djvu/729

Rh have been developed for inter-communicating purposes among a group of stations. These systems have been used to a considerable extent with telegraph circuits obtained from telephone circuits.



One of these systems employing motor-driven distributors at each station is shown in fig. 6. The sending distributor at one station and the receiving distributor at the other are indicated in detail. The distributor brush arms driven through a friction clutch are normally held stationary by a latch and make one rotation for each character transmitted or received. A start impulse, usually the opening of the line circuit for a brief interval, releases the receiving start latches so that all receiving distributors start rotating. The five impulses of the Baudot code which follow the start impulse are distributed properly to the selecting magnets or elements of a printer by the receiving distributors if their speeds coincide approximately with that of the sending distributor. Close synchronism is not required since all distributors are stopped and caused to start from the same initial position for each character.



An important feature is the method by which any receiving station can interrupt the sending station and obtain control of the circuit. As shown, this is accomplished if the line circuit is interrupted by the break key during the time the sending brush is passing over the sixth segment when a break relay at the sending station will be energized to open the circuit of the magnet controlling the latch. The release key will then have to be operated to permit further sending. This printing system has been used to a considerable extent for news distribution, where in many cases a number of sending and receiving stations are connected to one circuit and means must be provided to allow any station to obtain control of the circuit. Keyboard arrangements which may be used for perforating tape or for sending directly to the line have been developed and found very satisfactory for this kind of service. The Western Electric type-bar printer has been found very satisfactory for news service. This is provided with a stationary paper platen and a moving type-bar basket. Books containing carbon paper for making a large number

of copies and forms holding wax stencil sheets may be readily inserted into the machine. Means are provided for adjusting the strength of the blow of the type bars so that one to twenty copies can be secured.

(c) Cipher Printing System.—A. printing system for rapidly ciphering and deciphering telegraph messages has been developed. It is thought that cipher messages prepared by this system are absolutely unbreakable. It was successfully applied by the U.S. Army Signal Corps during the war and tests made indicate that messages can be ciphered and deciphered by this means with greater accuracy and many times faster than by other methods.



This system was developed by the engineers of the American Telephone and Telegraph Company. Its principles are illustrated in fig. 7. A message prepared in perforated tape form by the ordinary printer perforator passes through transmitter A. This would ordinarily control the selecting magnets of a printer or an automatic perforator. Key tapes B and C, however, passing through ordinary tape transmitters, control relays which interfere with the normal operation of the selecting magnets so that the resultant selection for any character of the message may be any one of the characters of the Baudot code. The characters of the key tapes are selected at random and B is one unit less in length than C. All tapes are stepped in unison. Repetition in the resultant key will not occur until B has revolved 1,000 times. The proper starting position of the key tapes B and C for any message may be indicated by six characters which may be