The Bell System Technical Journal 



October, 1926 



Radio Signaling System for the New York 

 Police Department 



By S. E. ANDERSON 



Synopsis: By means of the radio signaling system descril)ed it is pos- 

 sible, through the addition of a comparatively simple attachment to a stand- 

 ard radio telephone transmitter, to modulate the carrier with an audio 

 frequency tone in such a manner as to provide for calling individually, simul- 

 taneously, or in a number of designated groups, any one of several hundred 

 radio receiving stations. At the radio receiving stations apparatus is pro- 

 vided which may be operated from commercial sources of power supply and 

 by means of which a visible or audible signal is given to the operator that a 

 message is about to be broadcast, to which he should listen. Signals are 

 also provided which, in case of improper operation, immediately inform the 

 operator of the points at which attention is required. 



Introduction 



FOR some time the New York Police Department has been em- 

 ploying the mimicipal broadcasting station WNYC to broadcast 

 descriptions of missing persons and other features of police work in 

 which it is desired to enlist the cooperation of the public. The success 

 of this program has been such that the Police Department wished to 

 equip the precinct houses and police booths located in various parts of 

 the city with receiving sets with which they could listen in on com- 

 munications from the headquarters station WNYC. The fundamental 

 requirement was signaling apparatus incorporated in the receiving 

 sets which would attract the attention of the attendant at the proper 

 times. The system which was finally developed by the engineers 

 of the Bell Telephone Laboratories, Inc., in cooperation with the 

 New York Police Department is an excellent illustration of the 

 adaptability of wire practices to the radio field. The underlying 

 principles employed and much of the apparatus used had previously 

 found extensive application in the Bell System and elsewhere. 



The basis of this system is the Western Electric telephone train 

 dispatching system which is in rather general use on railroads through- 

 out the world for the purpose of providing selective signaling on their 

 train dispatching telephone systems. For every division, these 

 systems consist ordinarily of a single line to which are connected a 

 number of stations capable of being called by the dispatcher in- 



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