ANALYZER FOR COMPLEX ELECTRIC WAVES 



233 



interfere with the measurement in some other manner. This difficulty 

 is minimized in two ways: first, the ampHtude of undesired compo- 

 nents is reduced relative to the component under observation, by using 

 selectivity of the type previously described, before impressing the 

 wave on the modulator; second, the modulator is made of a balanced 

 type which permits efficient heterodyne action between the selected 

 component and the heterodyning current, but which gives very little 

 intermodulation between such components as remain after the initial 

 selection. The partial elimination of undesired components before 

 modulation is of further advantage in preventing unnecessary loading 

 of the modulator, which might tend to give it different efficiencies with 

 the complex current and with the sine wave calibrating current. 



Description of Apparatus 



A schematic diagram showing the several functional elements is 

 given in Fig. 1. The units have been arranged in the order in which 



Sro REirCRENCE: 



osc. 







e- 



CURRENT TO BE 

 MEIASURED 



HETERODYNE 

 OSC. 



HIGH 

 FREQUENCY 

 'AMPUrCR 8 

 SELECTIVE 

 CIRCUIT "t 



HIGH 

 FREQUENCY 

 'AMPLIFIER &" 

 SELECTIVE 



ciRcurr "2 



LOW 



fREQUENCY, 



AMPLIFIER 



RECTIFIER 



DC METER 



Fig. 1 — Schematic diagram of heterodyne current analyzer 



the measuring current would proceed, which is also the order of as- 

 sembly of the completed instrument. In the following, a more detailed 

 description will be given of the individual units. 



High Frequency Amplifiers. The circuit for the first unit is shown 

 in Fig. 2 and for the second unit in Fig. 3. These circuits differ 

 mainly in the output terminations of the second tube. The first high 

 frequency unit consists of a simple series tuned circuit together with 

 two amplifier tubes. In the tuned circuit is also included the coupling 

 resistance, R, for controlling the input to the amplifier. The sharpness 

 of resonance will therefore depend to some extent upon the value of this 

 resistance, but under most operating conditions it is relatively small in 

 comparison to the total effective resistance which includes that of one 

 tuning coil and the condensers. 



In both of these circuits the A.C. input voltage to the first tubes is 

 obtained from the drop across the condensers. If it is desired to dis- 



