636 BELL SYSTEM TECHNICAL JOURNAL 



Features of Monitoring Teletypewriters 



In connection with private wire teletypewriter service it has been 

 found very desirable to have so-called monitoring teletypewriters in 

 the repeater offices to facilitate testing between offices and with the 

 subscriber stations. These machines must be adaptable to work with 

 any subscriber's machine and to be usable for making test measure- 

 ments on circuits. 



The No. 14 tape teletypewriter has also been adapted to this service. 

 It may be equipped with an end of line indicator to facilitate communi- 

 cation with a page teletypewriter. Also since commercial service is 

 given at speeds of 40 and 60 words per minute, many of the monitoring 

 machines are equipped with two-speed governors and a switch to 

 provide for changing from one speed to the other. These machines 

 are also usually arranged for normal operation from commercial power 

 supply but emergency operation from the 130- volt telegraph battery. 



For making test measurements over circuits a special orientation 

 scale is provided together with a small crank extending through the 

 cover for quickly shifting the orientation setting to any desired point. 

 With the machine carefully adjusted to be practically free of harmful 

 distorting effects on the signals, it may then be used for measuring 

 distortions in received teletypewriter signals, the scale being arranged 

 to read the total distortion directly in percent of a pulse length. 



Tape Storage Transmission 



A heavy volume of traffic may be transmitted rapidly and con- 

 veniently by the use of perforated tape. In this method a machine 

 known as a perforator and having a keyboard like that of the teletype- 

 writer is used for punching the code signals for the message in a strip 

 of paper tape. This may be done with simultaneous typing of the 

 message on the teletypewriter in which case the speed of perforating 

 is limited to the speed for which the teletypewriter is set. If a typed 

 record is not made simultaneously with the perforating, punched tape 

 may be prepared at practically any speed within the capabilities of the 

 operator. This punched tape may then be fed through a device known 

 as a tape transmitter which automatically transmits the message 

 signals from the tape at the maximum speed for which the teletype- 

 writers connected to the circuit are set, which is usually 60 words per 

 minute. 



The method of transmitting from perforated tape has the distinct 

 advantage of using the line at maximum efficiency at all times as com- 

 pared with direct keyboard sending where pauses in operating the keys 



