lUnrO SIGNALING SYSTEM 



331 



Description of Aim>aratus 

 Transmitter Attachment 



A photograph of the transmitter attachment is shown in Fig. 1, 

 and a schematic circuit is given in Fig. 2. The apparatus consists 

 of a vacuum tube oscillator and a number of calling keys. These 





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Fig.l — Transmitter attachment 



TRHTiSMITTER flTTfiCHMENT 

 NEW YORK CITY POLICE RdDIO ^IGNBLmC SYSTEM 



Fig. 2 — Schematic of transmitter attachment 



keys, which are connected in parallel, are in series with the plate 

 winding of the oscillator coil. Operating any one of the calling keys 

 opens and closes its contacts in a regular sequence determined by the 

 code for which the key is set. Five group keys and a master key are 



