600 BELL SYSTEM TECHNICAL JOURNAL 



as for the disk receiver, by a potentiometer in the low frequency 

 portion of the circuit. The carrier ampUtude, however, is adjusted 

 by varying the plate potential applied to the oscillating tube. The 

 coupling to the lamp is made by connecting the central helix and the 

 distributor brush across a portion of the condenser of the oscillating 

 circuit. 



The frequency-amplitude relation of the envelope has been made 

 practically constant by employing resistance capacitance coupling in 

 the signal input amplifiers, by providing extremely high inductance 

 retard coils for the modulator — which is of the Heising type — and by 

 inserting resistance in the oscillating circuit to provide sufficient 

 damping. The relations between the original picture signal and the 

 envelope of the high frequency wave, with respect to both amplitude 

 and phase shift, were observed over the signal frequency range by 

 means of a Braun tube and found to be satisfactory. The impedance 

 of the connecting leads to the commutator was also measured and 

 found to have a negligible effect on the frequency and damping of 

 the oscillating circuit. 



It has been found that there may be a lag between the time when 

 the potential is applied to an electrode and the time when the gas 

 breaks down. This is especially true following an interval during 

 which there has been no discharge within the tube. Because of 

 this those electrodes which are the first to be connected in any one of 

 the parallel portions of the tube may fail to light. To overcome this 

 effect a small pilot electrode is kept glowing at the left-hand end of 

 each tube, thus irradiating the branch in such a way that the illumina- 

 tion of all electrodes follows immediately upon the application of 

 potential. These pilot electrodes, which are obscured from view of 

 the audience by the frame of the grid, are supplied by means of an 

 auxiliary connection to the oscillator with a potential somewhat 

 lower than that ordinarily impressed upon the picture segments. 



Appendix I 



The signal of Fig. 13 in the body of the paper may be represented 

 as follows: 



/(O =0 for / < 



t 



^ ior < t < T 



= 1 for / > r 



or by a Fourier integral in the form 



(1) 



