r 



COAXIAL CABLE SYSTEM FOR TELEVISION TRANSMISSION 449 



original frequency band as well as the upper and lower sidebands, 

 so that there will be a confusing jumble of frequencies in the modu- 

 lator output. For this reason a double modulation method was used 

 for the recent experiments. 



Fig. 10— Photograph of one of the special cathode ray receiving tubes. 



The modulating scheme employed can be followed with the help of 

 Fig. 11, which shows the two modulating steps at the sending end and 

 the two demodulating steps at the receiving end in four lines beginnmg 

 at the top. A carrier of 2376 kc. is used for the first modulation, 

 which results in a lower sideband from 1570 to 2376 kc. and an upper 



