358 



BELL SYSTEM TECHNICAL JOURNAL 



the position shown dotted in Fig. 13 the output comes from point a 

 since d is not coupled and b and c cancel each other. By shaping the 

 two rotors so that the difference in exposure to opposite stator plates is 

 proportional, respectively, to the sine and cosine of the angle of shaft 

 rotation, the total current flowing from the two rotors will be constant 

 and of phase proportional to the shaft angle. This is illustrated by 

 the vector diagram in Fig. 13 in which j3 is the shaft angle and vectors 

 a — d and b — c are the quadrature rotor outputs proportional to 

 sin j8 and cos /?. 



These phase shifters vary in output by less than ± 5 per cent as the 

 shaft is rotated. The departure from linearity of phase shift is corre- 

 spondingly small; i.e., less than ± 5 degrees. 



Fig. 14 — -The phase shifting condenser. 



The useful band width of this type of phase shifter is fundamentally 

 limited by the fact that l/coC varies with frequency while R does not. 

 However, this limitation does not appear in the Holmdel MUSA in 

 which the percentage band width is small because the phase shifters 

 operate at the intermediate frequency of 396 kilocycles. 



The phase shifters are connected to the steering shaft with helical 

 gears of multiple ratios as shown in Fig. 15. The phase shifter shafts 

 may be slipped with respect to the main shaft. After they have been 

 aligned so that locally supplied equiphase inputs to all detectors add in 

 phase at the point where the phase shifter outputs are combined they 

 are locked. This adjustment is independent of signal frequency. 

 Provision is made for adjusting the gain of each of the six phase shifter 

 circuits so that the differences in transmission-line loss may be com- 



