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BELL SYSTEM TECHNICAL JOURNAL 



looks lower New York Bay, and provided antenna heights up to 28 

 meters above sea level. 



The receivers were, for the most part, triple detection sets with 

 calibrated attenuators in the second intermediate frequency amplifier. 

 To this extent they were similar to familiar types of sets used to 

 measure field strengths on short waves ^^ and were capable of making 

 accurate comparisons of voltages induced in the receiving antenna. 



None of the usual means for introducing a calibrating voltage in the 

 set was provided. Instead, a method due to R. C. Shaw was used, 

 in which calibrations were made by producing at the antenna itself a 

 known field from a local source to which the name "standard field 

 generator" ^^ has been given. The standard field generator is a small 

 compact self-contained oscillator which is very carefully shielded 

 except for a small balanced loop extending in a vertical plane above 

 the shield (Fig. 1). A thermomilliammeter is located in the loop at 



Fig. 1 — Standard field generator. 



" In fact, one included a set similar to that described by Friis and Bruce {Proc. 

 I. R. E., 14, 507-519, Aug. 1926). An extra ultra-high frequency combination 

 (input circuits, beating oscillator, detector and amplifier) provided input at 6 mc. 

 to the standard short wave receiver. The latter was tuned to operate at 6 mc. 



" Since the writing of this paper, our attention has been called to the method 

 described by K. Sohnemann, E. N. T., 8, 462, Oct. 1931. The Sohnemann method 

 also uses a standard field generator but otherwise the technique is entirely different 

 from that of the Shaw method. 



