12-9] SPECIAL DISPLAY DEVICES 671 



The major difficulty in mechanizing the ELF screen is in the signal 

 distribution problem of placing a pulse voltage at the proper ferroelectric 

 element without resorting to an extremely expensive matrix array of diodes. 

 An electronic distribution system such as is shown in Fig. 12-46 illustrates 

 the elements necessary to perform the operation of placing a signal at the 

 proper point at the proper time. A keying pulse source for the horizontal 

 and vertical keying pulse distributer must be added to address the video 

 pulse to the matrix ELF point. In a radar display of the B scope type, the 

 horizontal pulse distributer could possibly be a mechanical commutator, 

 while the vertical distributer could take the form of a delay line. The 

 method illustrated can be considered a line-sequential system in that 

 intermediate storage capacitors are made simultaneously to charge up the 

 corresponding screen element as the horizontal switch commutates on a 

 line-by-line basis. It is, of course, important to add erase capability to this 

 circuit. This is accomplished by developing a pulse such that the previous 

 line of information is removed before new video information is placed on 

 the intermediate storage capacitor. The construction of the ferroelectric 

 control and the distribution system is a formidable problem. The fabri- 

 cation techniques being applied include evaporation for forming the 

 electrode pattern on the electroluminescent phosphor layer and printed 

 circuit techniques used to deposit the ferroelectric capacitors, intermediate 

 storage capacitors, diode switches, and even the high-frequency distributer 

 (delay line). It is anticipated that a resolution of a few hundred lines to 

 the inch will eventually be realized. 



Beam-Shaping Tubes. The ordinary CRT, as well as the storage 

 tube version, is capable of presenting two-dimensional information. In the 

 discussion of the various displays we have seen that the radar systems 

 usually require a means for presenting additional information. It was 

 mentioned that one or more additional guns in the same envelope or time 

 sharing of a single gun is used to display the required additional information 

 on the same screen. Additional information in the form of symbols may 

 also be displayed by means of specially designed "beam-shaping" tubes 

 such as the Typotron^^ and Charactron.^^ In this type of tube a stencil 

 containing the symbols has been inserted in the electron path. Usually the 

 stencil contains 64 symbols arranged in 8 lines and 8 columns. Two sets of 

 deflection plates or coils are needed, one set for selecting the symbol and 

 one set for positioning it in the correct place on the screen. By proper 

 coding of the symbols, considerable information may be presented on the 

 screen. Generally one of the symbols on the stencil is selected when the 

 beam is required to write ordinary CRT information. 



i^Trade name, Hughes Aircraft Co. 

 "Trade name^ Stromberg Carlson Co. 



