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The video source was the composite output of a consumer Hi-8 single chip camera with 410,000 pixels. The test pattern used in the first tests was a standard resolution pattern with wedges covering 200 to 800 TV lines. The outdoor scene was a wide angle shot of a maple tree in spring without leaves requiring the resolution of fine detail in the many branches. The test pulse was a square wave of about 95 kHz and a rise time of 12 nanoseconds. |
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The TV monitor was a Heathkit GR-2000 modified for Y/C and composite inputs and with a discrete component low phase shift Y delay line for flat video frequency response. This camera and monitor show the full 330 lines of horizontal resolution of standard NTSC, but have no hyped up video high frequencies to exagerate details.
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The 2 m. cable was a standard video cable.
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The 15 m. and 31 m. cables were standard 16 guage AC extention cords, seasoned by years of use outdoors. The 46 m. cable was these two plugged together.
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The differences between the short video cable and the long AC extention cords was subtle in the pictures and much easier to see on an oscilloscope with the square wave source. The main failing of the long cable was a rounding of the rise time and a loss of level of 5% or 0.5 dB.
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The conclusion is one may use darn near anything for video cables up to 15m. (50 ft.). For longer cables resistance and characteristic impedance start to have some signifcance.
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Monitors and video sources with substantial amounts of boosted high frequencies for hyped detail may make the difference in high frequency response easier to see. If your taste runs to that sort of "sharp" but flat TV look, be more a little more conservative in cable selection than these tests suggest.
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