RADIO TRANSMISSION SYSTEM FOR TELEVISION 



641 



stages of radio-frequency amplification, a detector, and two audio 

 stages of conventional design employing transformer coupling. No 

 serious difficulty was encountered in obtaining ample selectivity to 

 insure satisfactory operation in the face of the strong local signals but 

 care was necessary in locating the receiver and in laying out the 

 antenna in order to avoid the inductive type of interference which is 

 almost always experienced in the immediate vicinity of a large radio 

 station. The receiving antenna was located approximately 700 feet 

 from the two transmitting radiating systems. 



Fig. 5- 



-Radio receiving equipment for the television and speech channels in the 

 auditorium of Bell Telephone Laboratories, New York 



The receiver employed at the New York terminus of the television 

 channel presented a somewhat knotty problem on account of the 

 relatively wide frequency band which it was required to pass while 

 providing the maximum discrimination against interference. The 

 width of the required band pointed very definitely toward the super- 

 heterodyne. This type of circuit is also very stable, permits of all 

 the amplification that may be needed or that may be employed under 

 ordinary noise conditions, and is very selective against interference 

 immediately adjacent to the desired band. It is quite susceptible, 

 however, to interference from components differing from the desired 

 carrier frequency by an amount approximately equal to the inter- 

 mediate frequency. If the interfering component lies in the neighbor- 

 hood of the frequency of the oscillator, beats will be produced which 



