RADIO TRANSMISSION SYSTEM FOR TELEVISION 651 



other component must be rectitied to derive the original speech signal, 

 which may then be impressed on the loud speaker amplifiers. 



The reception scheme actually employed during the experiments 

 was somewhat different. The television signal was received separately 

 by means of the triple detection set employed for the demonstration. 

 The speech signal was received in a similar manner employing the set 

 utilized for the speech channel during the demonstration. This 

 latter receiver was tuned to 1545 kilocycles. That reception in this 

 manner is feasible, is evident from the diagram. The 1540-1550- 

 kilocycle zone contains two speech sidebands and a carrier of 1575 

 — 30 or 1545 kilocycles. It is quite possible, therefore, to demodulate 

 in one step, instead of "beating" the various components against the 

 main carrier (1575 kilocycles) to produce a 30-kilocycle supplementary 

 carrier which must be rectified a second time to derive the speech 

 signal. The 1600-1610-kilocycle band was ignored. The receivers 

 were sufficiently selective that, with the 5-kilocycle interval which 

 existed between the two bands, no noteworthy crosstalk was ex- 

 perienced. 



The results obtained in this manner were not as satisfactory as those 

 to be had with the other system described. This can be attributed to 

 two factors, both concerned with the transmitting apparatus: (1) In 

 order to transmit both signals with the same transmitter, that is, 

 the same vacuum tubes, the individual current amplitudes had to be 

 reduced to at least one half, resulting in too weak a radio signal to 

 clear the prevailing noise levels in New York, (2) In spite of the 

 reduced amplitudes, a certain amount of inter-modulation was ex- 

 perienced in the transmitter which resulted in "crosstalk" between 

 the channels. Notwithstanding these deficiencies, however, it was 

 possible to recognize the speaker and to understand his remarks; 

 but a short time ago, the performance would have been considered a 

 very noteworthy achievement. 



Experiments of this nature, although not new, are of particular 

 interest where television is concerned, since, as Dr. Ives has indicated, 

 the logical trend of development is toward a finer picture structure 

 involving the transmission of much wider frequency bands, or what 

 is more likely, the use of parallel scanning schemes and multi-channel 

 transmission. The work, while necessarily somewhat cursory, may, 

 therefore, be of value in affording an indication of the significance of 

 multi-channel radio transmission in this connection. From a popular 

 standpoint, these tests have been described as the transmission of 

 both voice and image "on a single wave-length." To what extent this 

 statement falls short of actually representing the facts in the case is 



