VISUAL INDICATORS 



(20th Century Electronics, Ltd.). Multi-gun tubes are expensive, however, 

 and there are two other possibilities. 



Beam-switching — A single gun tube is used, and the Y deflection system is 

 connected serially to a number of input quantities. If the switching rate is 

 fast enough it appears as if there were a number of distinct traces on the 

 screen. Woods^° and Wood and Keenan^^ may be consulted. 



Voltage coincidence — This has been discussed by Reeves^^ and the author^^. 

 The C.R.T. spot is made to scan rapidly over the entire height of the screen. 

 The alternating voltage which causes this is also applied to a bank of cir- 

 cuits in which it is compared with the signals to be displayed. Whenever 

 the scan voltage coincides with the instantaneous value of one of the signal 

 voltages, the spot is momentarily brightened. In reference 13 the whole 

 question of multi-channel presentation is discussed, and an attempt has been 

 made to show that the voltage-coincidence method scores heavily in cheapness 

 for a small number of channels, and in frequency response for a large 

 number. 



REFERENCES 



1 Strafford, F. R. W. Wireless World 59 (1953) 90 



^ ScROGGiE, M. G. Radio Laboratory Handbook London; Iliffe 



3 DE Gruchy, J. Wireless World 59 (1953) 425 



4 Johnson, G. Wireless World 61 (1955) 31 



5 COLLINSON, J. D. Wireless World 61 (1955) 428 

 « Davies, J. R. Wireless World 61 (1955) 297 



■^ Fleming Williams, B. C. Wireless Engineer 17 (1940) 61 

 ^ MouLLiN, E. B. The Principles of Electromagnet ism Oxford ; Clarendon Press 

 ^ Cocking, W. T. Television Receiving Equipment London ; Iliffe 

 1" Woods, R. W. Electronics 28 (1955) 135 



11 Wood, K. E. and Keenan, T. C. Electronic Engineering 28 (1956) 105 



12 Reeves, R. J, D. Wireless World 62 (1956) 85 



1^ Donaldson, P. E. K. Electronic Engineering 29 (1957) 78 



470 



