REMOTE CONTROLLED LINE CONCENTRATOR 269 



tive pulses are employed. Diodes are placed in the legs of a center tapped 

 transformer, as shown in Fig. 15, to select the polarity of the trans- 

 mitted pulses. At the receiving end the desired polarity is detected by 

 taking the signal as a positive pulse from a properly poled winding of a 

 transformer. The amplifier, as described in Section 6c responds only to 

 positive pulses. If pulses of the same polarity are transmitted in the 

 other direction over the same pair, as for control pair No. 1, the outputs 

 of the receiving amplifier for the same polarity pulse are inhibited 

 whenever a pulse is transmitted. 



As shown in Fig. 15, the service request and line busy signals are 

 transmitted from the concentrator to the central office over one pair of 

 conductors as positive and negative pulses respectivel3^ The trans- 

 mission of these pulses gates the outputs of two of the receiving ampli- 

 fiers at the concentrator to permit the receipt of the polarized signals 

 from the central office. This prevents the pulses from being used at the 

 sending end. A similar gating arrangement is used with respect to the 

 signals when sent over this control pair from the central office. The pulses 

 designated VG or RS never occur when a pulse designated SR or LB 

 is sent in the opposite direction. The transmission of the VF pulse over 

 control pair No. 2 is processed by the concentrator circuit and becomes 

 the SR or LB pulses. Li section 7 the purpose of these pulses is described. 



The signaling range objective is 1,200 ohms over regular exchange 

 area cable including loaded facilities from sfation to central office. 



h. Power Supply 



Alternating current is supplied to the concentrator from a continuous 

 service bus in the central office. The power supply path is a phantom 

 circuit on the two control pairs as shown in Fig. 16. The power trans- 

 former has four secondary windings used for deriving from bridge 

 rectifiers four basic dc voltages. These voltages and their uses are as 

 fofiows: —16 volts (regulated) for transistor collector circuits and gate 

 biases, -|-5 volts (regulated) for transistor base biases, -|-30 volts (regu- 



, lated) for crosspoints holding circuits and — 65 volts for the marking and 

 operating of the line crosspoints. For this latter function a reference to 

 the central office applied -flOO volt trunk mark is necessary. The refer- 

 ence ground for the concentrator is derived from ground applied to a 

 simplex circuit on the power supply phantom circuit. Series transistors 

 and shunt silicon diodes with fixed reference breakdown voltages are 



I used to regulate dc voltages. 



