1324 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1954 



Fig. 10 — Front view of the 2,600-cycle signaling panel. 



The R delay, because of guard action and the fact that its secondary 

 winding is closed through a varistor and resistance, is relatively slow to 

 operate and fast to release. For this reason some foiTn of pulse correction 

 is necessary to get good dial operation. This is obtained with the rg 

 (regenerate) relay and its associated cr timing network, and there re- 

 sults an output pulse within the needed limits, even though the signal on 

 the R relay is shortened considerably. 



DESCRIPTION OF 2,600-CYCLE DESIGN 



The 2,600-cycle unit, shown in Fig. 10, is just half the size of the 1,600- 

 cycle unit, costs less than half as much, and is of the "plug in" type so it 

 can be readily replaced for maintenance action. 



A simplified diagram of the new signaling circuit is shown in Fig. 11, 

 with the transmitting portion in the upper part of the figure and the 

 receiver in the lower part. The transmitting portion employs three re- 

 lays designated m, hl, and co which are interconnected to perform the 

 following functions: relay m is used to key the signaling tone; relay hl 

 (high level) adds 12 decibels to the tone power at the beginning of each 

 signal tone application to improve signal reliability in the presence of 

 line noise and variations in attenuation; and relay co (cut off) cuts the 

 line momentarily to prevent noises originating in the switching equip- 

 ment from interfering with signaling. 



