COAXIAL CABLE SYSTEM FOR TELEVISION TRANSMISSION 447 



imagined which will produce a pronounced component at any given 

 frequency, hence, it is deemed important to transmit the entire band 

 from to 806 kc. 



Receiving Device 



At the receiving end an effort was made to obtain as high a degree 

 of fidehty of reproduction as possible. No small factor in the success 

 of the recent experiment was the special cathode ray tube, designed 

 by Dr. C. J. Davisson and used at the receiving end to display the 

 transmitted picture. Some of the features of this tube are indicated 

 schematically in Fig. 9. A stream of electrons from the cathode 

 passes through a series of electron lenses which focus a narrow beam 

 on an aperture .006" square. Between the lenses and the aperture, 

 however, are two modulating plates connected to the incoming circuit 

 in such a way that there appear on these plates potentials varying 

 according to the voltage of the incoming signals. The effect of 



DEFLECTING 

 PLATES 



MODULATING 

 PLATES 



ELECTRON 

 LENS SYSTEM 



Fig. 9 — Schematic diagram of the special cathode ray tube used for viewing 

 transmitted images. 



potential on these plates is to deflect the electron beam, and the 

 conditions are such that at maximum strength of signal practically 

 the entire stream of electrons passes through the hole and forms a 

 brilliant spot of light on the front of the tube. As the signal decreases 

 in strength, the electron stream is more and more deflected; less 

 electrons pass through the aperture, and the illumination on the 

 sensitized end of the tube decreases. 



In addition to these modulating plates, and placed between the 

 aperture and the front of the tube, are two other pairs of plates 

 mounted in planes at right angles to each other. The potential on 

 one of these sets of plates, controlled by a frequency of 5760 cycles, 

 which is the frequency at which successive lines are scanned, varies in 

 such a way that the beam of electrons passing through the aperture 

 is swept across the front of the tube from left to right, exactly in 

 synchronism with the scanning beam at the sending end. After the 

 beam reaches the farther side of the picture, the potential on the 



