256 THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1951 



Cords 



Neoprene jacketed handset and mounting cords are used with the new set. 

 In locations where cord maintenance is unusually high, and especially where 

 severe moisture conditions prevail, neoprene jacketed cords are used with 

 the present combined set. 



A four-conductor handset cord is used to separate the transmitter and re- 

 ceiver circuits. This introduced design problems in providing a cord of pleas- 

 ing appearance, small diameter and light weight appropriate for the new 

 handset. A new tinsel cord construction was developed employing fewer 

 tinsel threads and a reduced size of center core thread which resulted in a 

 15% decrease in the overall diameter of the handset cord even though the 

 number of conductors has been increased from three to four. 



A grommet molded to this cord reinforces it at the point where it enters 

 the handset. By properly proportioning the taper of the grommet the 

 severe flexing that would normally occur in service is distributed over an 

 appreciable length of the cord thus decreasing the effect of such flexing on 

 the life of the cord. The grommet also provides an acoustic seal for the 

 cavity through the handset handle to the back of the receiver, thus pre- 

 venting extraneous acoustic noises from reaching the back of the receiver 

 unit. It also has a notch which fits a projection in the handle, thus anchoring 

 the cord in the handset. Laboratories tests on the new cord with the grommet 

 indicate that its service life will exceed that of previous designs. 



In the new cord the conductors are not twisted but lie straight and parallel 

 for the length of the cord. The parallel construction facihtates manufacture 

 with respect to automatic stripping of the jacket and tipping of the con- 

 ductors at the cord terminations. 



Did 



As previously discussed, the new dial presents an entirely new appearance 

 feature in the set. In addition, the dial mechanism is a complete new de- 

 velopment in the interest of improved performance and economy of manu- 

 facture and is protected against dirt. Improved performance of the dial 

 arises chiefly from the closer control realized both in manufacture and in 

 service over the pulsing characteristics and speed regulation of the dial. By 

 controlUng the time of both the break and make of the dial pulsing contacts 

 to narrower limits than in the present dial appreciable extension of dialing 

 range is possible. 



In the new dial a tolerance of rb 2% was set for the per cent break of the 

 pulsing contacts. This is in contrast to double this range for the present 

 dial. The normal operating speed of the dial is controlled to 10 =t 0.5 pulses 

 per second instead of 9.5 ± 1 pulses per second as at present. Further, the 

 design is such that it is confidently expected that this better performance 



