Analyzer for Complex Electric Waves 



By A. G. LANDEEN 



IN problems concerned with the electrical transmission of intelligence 

 it is necessary to have means for studying complex electric waves- 

 In certain steady state conditions these complex waves become 

 periodic, and, although not sinusoidal as a whole, may be resolved into 

 a number of sinusoidal components. It is particularly important to be 

 able to measure these components indivadually. 



In studies on systems employing carrier currents which may be 

 transmitted over wire lines it is often necessary to measure a signal 

 wave component which may lie anywhere in the frequency range be- 

 tween 100 and 100,000 cycles per second. The most important range 

 at the present time is, however, below 40,000 cycles per second. In 

 addition to covering a wide range of frequencies these components may 

 also vary considerably in amplitude, both as to absolute value and as to 

 value relative to other components in the signal wave. 



For several years there has been in use in the Bell Telephone Labora- 

 tories special apparatus by means of which a single component of a 

 complex periodic current wave may be selected from the remaining 

 components and its amplitude determined. The sensitivity and 

 selectivity of this apparatus are such that components of small ampli- 

 tude may be accurately measured even in the presence of other com- 

 ponents of several hundred times the amplitude and differing but little 

 in frequency. With the latest improved form it is now possible to 

 measure current components having amplitudes as low as 10~^ amperes 

 with a possible error of 10 per cent. For such minute currents this is 

 within the error which might be introduced by the external apparatus 

 such as attenuators and thermocouples together with their calibration 

 charts. 



Though the apparatus was primarily designed for use in current 

 wave analysis work, it may also be readily adapted to voltage analysis. 

 Suitably calibrated, it can be used also as a frequencyjmeter of extremely 

 high precision. 



Introduction 



The method of analysis here described had its origin in a circuit 

 built by J. W. Horton in 1917. This had a resistance coupled tuned 

 circuit responsive to the component desired. Following the tuned 

 circuit two stages of amplification were used to magnify the selected 

 current. This current was then passed on to a third unit where it was 

 rectified and measured by a D.C. meter. It was evaluated directly by 



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