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BELL SYSTEM TECHNICAL JOURNAL 



nominal 180° network. The amount the standard phase-shifter failed to 

 return to the original starting point indicates the residual error of the 180° 

 network. The 180° network is adjusted accordingly and the procedure 

 repeated until an error is no longer discernible. Thus the 180° point on the 

 phase-shifter scale can be determined. In similar fashion, by combination 

 of the 180°, 90° and 60° networks, calibration points in multiples of 30° are 

 obtained. The equivalent of a 10° network is obtained by use of the ±5° 

 scale on the indicator and scale factor adjustment. Interpolation to 1° 

 is then made using the scale divisions on the indicator. Calibration to an 

 absolute accuracy of ±0.1° was found adequate for use in the measuring 

 system. Much higher accuracy could be obtained if the need arose. There 

 appears to be no inherent frequency limitation in this calibration method. 



AUXILIARY 



SIGNAL 

 OSCILLATOR 



PHASE 



SHIFTER 



0-360° 



CONTINUOUS 



LI 11 J 



STANDARD 



PHASE 



SHIFTER 



0-360° 



CONTINUOUS 



PHASE 

 INDICATOR 



Fig. 12 — Phase shifter calibration circuit. 



Conclusion 



The design efifort has been directed toward achieving laboratory precision 

 in measurement and at the same time maintaining the speed necessary for 

 production testing of transmission networks. 



The measurement of phase-shift is unambiguous with respect to quad- 

 rants and the measurements of insertion phase-shift and loss or gain are 

 independent of each other. The entire frequency range is covered without 

 band switching by use of a heterodyne signal oscillator and the system zero 

 is independent of measurement frequency. Detector tuning is eliminated 

 through the use of frequency conversion, employing a beating oscillator 

 automatically controlled in frequency by the signal oscillator. Phase-shift 

 and transmission may be read directly, without auxiliary computations. 



