16 THE BELL SYSTEM TECHinCAL JOURNAL, JANUARY 1951 



Such amplitude stabilization is needed to prevent excessive pulse distortion 

 from the slow rise and fall of pulse edges in the delay circuit. Only during the 

 transition periods between make and break can noises more than 7 db 

 below normal signal level cause pulse distortion. The cathode follower 

 supplies low impedance drive to the germanium rectifier which, with its 

 low resistance load, results in highly stable Operation. The delay circuit 

 functions primarily to discriminate against short duration noise bursts during 

 the off-hook signal condition. Unwanted relay operation at this time would 

 flash the operator or cause registration of a wrong number. The output 

 relay, which is of the mercury contact type, has a split winding for ease of 

 adjusting the per cent break and to minimize pulse distortion with 130-volt 

 battery variation. Bias change on the varistor rectifiers through the relay 

 contacts prevents excessive first pulse distortion despite the high amount of 

 delay used in the delay circuit. Control potentiometers in the circuit adjust 

 **just operate" sensitivity, relay current and per cent break. On-hook and 

 off-hook are sent from the signal receiver to the trunk circuit as open and 

 ground, respectively, on the "E" lead. 



Use of the N system as a part of the nationwide networks of dialing 

 intertoU trunks imposes strict limits on the amount of pulse distortion 

 contributed. The severest requirements are when operating into step-by- 

 step offices where pulses distorted beyond per cent break lunits of about 

 44-72 per cent may produce wrong numbers. A typical connection from a 

 dial and outgoing trunk over a two-link N connection into a step-by-step 

 office might be expected to have a distribution of pulse distortion as follows: 



During extreme battery and level conditions on one N circuit link about 

 =t 2% more pulse distortion can be expected. 



Carrier Frequency Transmitting and Receiving Circuit 



The third part of the channel unit is the carrier subassembly. It contains 

 a germanium varistor modulator and individual channel crystal carrier 

 oscillator in the transmitting circuit and the channel band filter, an auto- 

 matic gain control or channel regulator and a germanium varistor de- 

 modulator in the receiving circuit. Figs. 7(a) and 7(b) show the carrier 



