304 



BELL SYSTEM TECHNICAL JOURNAL 



When peaks on the record are so close together as to overlap 

 greatly, the reading on the scale is untrustworthy. If, instead of 

 a rectifier and direct-current meter, an alternating-current meter 

 giving deflections proportional to total r. m. s. values, were used, 

 it would be theoretically possible to determine the component fre- 

 quencies and amplitudes making up any composite peak, provided 

 the number of frequencies could be determined. This procedure, 

 however, would be impracticable. An examination of the theory 

 of the rectifier shows that the problem of separation of the com- 

 ponents of a composite peak is in general indeterminate. The rec- 

 tifier however resolves adjacent peaks somewhat better than an 

 alternating-current meter. 



The analyzer has been most used in the analysis of audio-fre- 

 quency currents for which the higher frequency range, 80-5000 

 cycles, is more useful. For the investigation of power problems the 

 lower range w'ould ordinarily be more suitable. In order to sim- 

 plify the change from one frequency range to the other the tuning 

 inductance only, is changed, leaving the mechanism for varying the 

 capacitance in steps the same for both ranges. Since the inductance 

 change in going from the high to the low-frequency range is in the 

 ratio 1:16 and the change in the frequency range 4:1, the abscissas 

 on the low-frequency records have one-fourth the value of those on 

 the high-frequency records. 



Since the smallest frequency divisions at the lower end of the 

 high-frequency records are 20 cycles, these divisions on the low-fre- 

 quency records are 5 cycles. There are, therefore, four times as 

 many steps of tuning in the same frequency inter\-al on the low as 

 on the high-frequency record. The low-frequency record is there- 

 fore not of minimum practicable length. Since the same input 

 network is used with the 20-1250 range as with the 80-5000 range, 

 the low-frequency records are not direct reading in input current, 

 but must be used with a calibration. Our use of the low-frequency 

 range, howe\er, has been so limited as not to juslif>' the preparation 

 of additional equipment for this use of the anah'zer. 



The apparatus is equipped with a device which permits of making 

 simultaneous analyses of two complex waves. The principal reason 

 for making such double records is to reduce errors in comparing two 

 sources which may vary with time. The device may also be used 

 simply to save time. It operates b\- roiniecling alternatcK' to the 

 analyzer the two complex wa\es in such a way that the record for 

 each wave is traced b\' points re])resenting alternate tuning con- 

 denser settings. 



