IMAGE TRANSMISSION SYSTEM 



463 



teristic of the image circuits when the image line equalizers are in- 

 cluded. 



Although the distance between the stations is small the require- 

 ments of the television system from the standpoint of freedom from 

 noise and other interference require that considerable care be given 

 to the selection of the cable circuits used. All terminal connections 

 are made through balanced repeating coils or transformers so that all 

 of the circuits are balanced to ground. Also, in order to insure that 

 the crosstalk between the various channels be unnoticeable the 

 terminal equipment is so adjusted that approximately the same amount 

 of power is transmitted by each circuit. 



Neon Lamps and Associated Circuits 



After amplification, the received television signal is impressed on 

 the grids of two power tubes in parallel to furnish current for a neon 

 receiving lamp. The terminal lamp circuit is shown in Fig. 12. 



» _ 



X 



Fig. 12 — Schematic of neon lamp circuit. 



The grid bias of the two power tubes is varied by the operator to 

 control the DC plate current, which replaces the original DC signal 

 component suppressed at the sending end. The quality of the re- 

 produced image is determined by the operator's control over the 

 relative levels of the incoming AC signal and the restored DC current. 

 The television current from the power tubes is translated back into 

 light by a water-cooled neon lamp designed to operate on a large 

 current. The structural details of the lamp are shown in Fig. 13. 

 Heavy metal bands attach the rectangular cathode to a hollow glass 

 stem occupying the central portion of the tube. Water from a small 

 circulating pump flows continuously through the glass stem and cools 

 the cathode by thermal conduction through the metal bands. To 

 reduce sputtering of the cathode and consequent blackening of the 



