Radio Transmission System for Television^ 



By EDWARD L. NELSON 



Synopsis: Starting from the general requirements imposed on the 

 transmitting medium, this paper discusses the engineering of a radio 

 system for television purposes and describes the radio facilities actually 

 employed for the recent Bell System demonstration. The tests to which 

 the system was submitted to determine its suitability are outlined and the 

 measured frequency-response characteristics are shown. An interesting 

 phenomenon due to multi-path transmission, the production of positive and 

 negative secondary images, is reported. A brief series of experiments con- 

 cerned with the transmission of both voice and image "on a single wave- 

 length" is also described. 



IN Other papers of this symposium, the general nature of the television 

 problem has been discussed, the scope of the recent Bell System 

 demonstration has been outlined, terminal apparatus for television has 

 been described, and the general requirements to be met by the trans- 

 mitting agency have been formulated. This paper is concerned with 

 the problem of engineering a suitable radio system for television 

 purposes and with a description of the radio facilities actually employed 

 for the demonstration. 



Requirements Imposed on the Radio System 



The radio experiments were conducted from the Bell Telephone 

 Laboratories' Experimental Station 3XN at Whippany, New Jersey. 

 Between this point and the main Laboratories Building at 463 West 

 Street, New York City, some 22 miles distant, three separate com- 

 munication channels were required — one for the picture, a second for 

 synchronizing, and a third for speech and music. The demonstration 

 being of a three-cornered nature involving New York, Washington 

 and Whippany, it was deemed to be highly advantageous to transmit 

 the necessary synchronizing currents for both the wire and radio 

 systems from a master generating set located in the auditorium of the 

 West Street Building. Hence the synchronizing channel was required 

 to operate from New York to Whippany, while the picture and speech 

 channels necessarily transmitted in the reverse direction. 



From the radio standpoint, the problem presented for solution 

 may be described as follows: 



L There is given television transmitting and receiving apparatus 

 designed to work into and out of specified impedances at stated signal 



^Presented at the Summer Convention of the A. I. E. E., Detroit, Mich., June 

 20-24, 1927. 



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