246 



THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1951 



and receiver design. In the case of the receiver, the design was new in basic 

 principles and resulted in the so-called "ring armature" structure which was 

 discussed in the January 1951 issue of the Bell System Technical Journal.^ 

 This structure is not only five db more efficient than the present handset 

 receiver, but also permits extending the upper frequency range by some 

 500 cycles. For compatibility with existing plant characteristics the general 

 response of the new receiver was kept flat as measured on a standard 6 cc 

 coupler as in the present receiver. 



O.OI 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 O.Il 0.12 0.13 0.14 0.15 

 CURRENT IN AMPERES 



Fig. 5 — Equalizer characteristics. 



While the transmitter design resembles superficially the current design, 

 it differs in many important respects. To get the required 5 db volume gain 

 on long loops required taking advantage of every design expedient in the 

 transmitter itself, as well as in the handset in which it was mounted. Modu- 

 lation of the carbon was increased, and the effective working acoustic pres- 

 sures were raised by using smaller parts and locating the transmitter more 

 advantageously with respect to the mouth. This is of particular benefit to 

 women, whose transmitted levels have hitherto been considerably less than 

 for men. 



Advantage was taken of new knowledge of granular carbon processing 

 to get initial d-c. power gain over present type transmitters, and by a new 



