RADIO TRANSMISSION SYSTEM FOR TELEVISION 



645 



output circuit of the water-cooled tubes. Employing a frequency of 

 1000 cycles, the input was adjusted to produce normal modulation 

 and the readings of the input and output meters noted. The oscillator 

 frequency was then changed by a convenient amount while holding the 

 input reading constant and the artificial line readjusted, if necessary, 

 to produce constant output current. Under these conditions, any 

 change in the setting of the artificial line indicates an equal variation 

 in the transmission efficiency of the transmitter which is evaluated 

 by this method directly in TU. 



The characteristic of the receiver was determined in a similar 

 manner. A low power transmitter of known characteristics was 

 connected to it through a suitable attenuating network which, in so far 

 as the receiver was concerned, simulated the receiving antenna. The 

 radio-frequency input to the receiver was adjusted to approximately 

 the normal value and a series of measurements taken with variable 

 audio-frequency inputs as indicated above. 



The overall measurements were also based on a similar procedure 

 impressing a constant input on the 600-ohm input terminals of the 

 transmitter through a suitable artificial line and adjusting the latter to 

 give a constant current into a 600-ohm load at the output of the 

 receiver, taking necessary precautions, of course, to preclude over- 

 loading at any point in the system. 



Fig. 7 — Measured characteristics of television channel 



The experimental characteristic curves thus obtained are shown in 

 Fig. 7, where the abscissae represent cycles per second and the ordinates 

 departure from the 1000-cycle value in TU. As will be noted, at the 

 lower frequencies exceptionally good performance was obtained, the 

 overall characteristic being only 2 TU down (or deficient) at 10 cycles 

 and only 6 TU down at 3 cycles. The results for the higher fre- 

 quencies, however, were not so satisfactory, a loss of approximately 



