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BELL SYSTEM TECHNICAL JOURNAL 



In order to measure yn , the output coaxial line was short-circuited at a 

 point an integral number of half-wave-lengths from the grid-anode terminals 

 of the tube. The admittance measured in the input line could then be used 

 in computing ^'n . To measure J22 , the procedure was reversed, the input 

 line being shorted, and the corresponding admittance being measured in the 

 output line. In either case the normalized line admittances were measured 

 by the standard procedure of determining the standing wave ratio in the 

 line and locating the position of the standing wave minimum with respect 

 to the equivalent terminals of the tube. 



The transfer admittances were measured with the equipment shown in 

 Fig. 17. The equipment shown here has been fully described in a recent 



TRANSFORMER 



GRID PLANE 



Fig. 16 — Circuit connected for measuring input short-circuit admittance of a triode. 



paper-" and will be described only briefly here. The output of a signal oscil- 

 lator is divided into two portions. One portion is applied to a balanced 

 modulator where it is modulated by an audio-frequency signal. The sup- 

 pressed-carrier, double-sideband signal from the modulator is applied to the 

 input circuit of the triode. Probes are provided for sampling the voltages 

 Vi and F2 at points an integral number of half wavelengths from the input 

 and output gaps of the tube respectively. The other portion of the oscillator 

 power is fed through a calibrated phase shifter and is applied to a crystal 

 detector in the manner of a local oscillator of a double-detection receiver. 

 The signal samples at V i and V 2 are then alternately applied to the crystal 

 detector where they are demodulated by the action of the homodyne carrier. 

 In each case the phase shifter is adjusted so that the audio signal disappears 

 in the detector output. This occurs when the phase of the homodyne carrier 



