IMAGE TRANSMISSION SYSTEM 



457 



doors to each group. The cells of each group are connected in par- 

 allel through the input resistance of a two stage resistance-capacity 

 coupled amplifier similar to those previously used. This raises the 

 level of the signal to such a point that the output of the three ampli- 

 fiers may be carried through shielded leads and connected in parallel 

 to a common amplifier. 



The metal anodes and lead wires of the cells in parallel in any 

 one group give an appreciable capacity to ground, which results in a 

 further loss in amplitude and phase shift of the high frequency com- 

 ponents of the signal. The combined loss introduced by ionization of 

 the gas in the cells and by capacity to ground is shown by curve B of 



Fig. 



7 — Schematic of interstage amplifier coupling to equalize for the high frequency 

 losses in the photoelectric cells. 



Fig. 6. This combined loss is equalized by an interstage amplifier 

 coupling, Fig. 7. The equalized output from the photoelectric cells 

 is shown by curve C, Fig. 6. 



Two-Way Image Signal Amplifiers 

 The vacuum tube system used to amplify the photoelectric cell 

 currents in two-way television is patterned closely after that used 

 previously in one-way television, and the description here will be con- 

 fined chiefly to novel features. These new features are necessary to 

 take care of the doubled frequency band which results when the 

 scanning is done with a 72-hole disc rather than with a 50-hole one, 

 and to provide sufficient power to operate the high intensity neon 

 lamp which is essential to two-way television. Certain other new 

 features have been introduced in order to simplify the apparatus and 

 to reduce the maintenance required to keep it in good working con- 

 dition. 



The vacuum tubes which operate at low energy levels are the 

 so-called "peanut" type, chosen because of their freedom from 

 microphonic action and their low interelectrode capacities. Protection 

 against mechanical and acoustical interference is secured by mounting 

 these tubes in balsa wood cylinders which are loaded with lead rings 



