TV Transmission 



The second aspect of the transmission problem is the necessity to 

 transmit near-real time TV pictures from the vehicle to the surface. 

 This problem is the hardest to solve and the most difficult to assess of 

 the cable problems. The number and size of coaxes required to transmit 

 the TV can significantly affect the size and weight of the cable. 



CURV III has three RG-59-type coaxes (0.2 inch in diameter) 

 to transmit signals from the two TV's over 8, 000 feet of cable. 

 To transmit without signal attenuation, two comparable TV signals 

 over 2 6, 000 feet of cable will require a significant increase in 

 size of the coaxes used. This increase in turn would radically in- 

 crease the size of the control cable. The ways of minimizing the 

 size of the coax are to accept slow-scan TV, accept less picture 

 quality, or develop new TV transmission techniques. A near real- 

 time picture is needed; the 20, 000-foot goal includes the capability 

 to do real-time work, making slow-scan techniques unacceptable. 

 It is not obvious what quality of picture is needed. The first step, 

 then, is to define the magnitude of the problem by determining 

 what picture quality is required and what attenuation and inter- 

 ference will be encountered in various coaxes. 



The quality of picture that is acceptable is important because it de- 

 termines the amount of attenuation that can be accepted. Since attenuation 

 is a direct function of the size of the coax, if less picture quality is accept- 

 able, smaller coaxes can be used. For example, in all coaxes the high 

 frequencies are attenuated more rapidly than the low frequencies. Atten- 

 uation of the high frequencies results in less resolution, the picture be- 

 comes blurry and the outline of objects is lost. To get 600 line resolution 

 requires a bandwidth of 8 MHz; whereas if only 400 line resolution is 

 needed, the bandwidth is only 5 MHz. If 400 line resolution is acceptable, 

 it might therefore be possible to use a coax that provides only 5 MHz of 

 usable signal after attenuation, rather than going to a larger coax that 

 provides the full 8 MHz after attenuation. 



How much effect reduced picture quality will have on the cable design, 

 of course , depends on the amount of attenuation. To get a feel for the mag- 

 nitude of the attenuation problems, an analysis was conducted assimiing 

 transmission over a RG-ll/U coax, which is approximately 0.4 inch in 

 diameter. It was found that regardless of equalization techniques (ampli- 

 fication of signal directly proportional to frequency) the maximum ampli- 

 tude of the received signal at the surface was too far below the main power 

 voltage (approximately 120 db below) to prevent main power interference. 

 Both pre-equaUzation and post-equalization of the signal were studied. It 



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