IN-BA\D SlXCiLE-FUKQllONCY SR!\AL1.\<J 



1327 



Dial pulses of 2,000-cyclG tone wltli various decrees of distortion enter 

 the circuit at the left of the diagram. It is desired that the}' be corrected, 

 converted to an interrupted do current in lead e by means of relay r, 

 and then passed on through the toll office. This ])reak in the dc curnnit 

 will effectively key the next outgoing tone transmitter, which faithfully 

 reproduces the break intervals. The k and hf relays are shown oix'iated 

 as would be the case if an originally short dial tone pulse were being con- 

 verted into a longer dc current l)reak in lead e, i.e., closer to (iO miUi- 

 seconds in duration. 



Currents of signal frequency build up voltages across the "signal 

 network," while currents of any other fre(iuency, such as those from 

 speech, build up voltages across the "guard network." These voltages are 

 rectified separately, as shown, to obtain oppositely poled d(^ voltages 

 across the signal capacitor s and the guard capacitor g. During normal 

 speech, the voltages across the guard capacitor will dominate and, being 

 negative, will keep the grid of dc amplifier b negative to prevent opera- 

 tion of the R relay at this time. 



However, when dial tone pulses are applied, the main voltage ^^^ll 

 appear across the signal capacitor, with a small transient voltage ap- 

 pearing across the guard capacitor due to sidebands of the dialing fre- 

 quency. This transient, being negative, produces an effect shown at (a) 



SERIES OF 

 INCOMING DIAL 



PULSES OF 

 2600 'V TONE 

 (TOO SHORT) 



GRID VOLTAGE 



ON DC 

 AMPLIFIER (B) 

 IN FIGURE 11 _6V 



OUTPUT CURRENT 

 IN CIRCUIT E 

 OF FIGURE n 



J 



CORRESPONDS TO 

 40 MS INTERVAL 



Fig. 12 — Wave forms for lengthening of short dial pulses. 



