🚀 go-pugleaf

 In article <4095@utcsri.UUCP>, gclark@utcsri.UUCP (Graeme Clark) writes:
 > 
 > I'm curious about the claims of a particular LAN design (FDDI) which
 > talk about sending video data and digital data over the same baseband
 > channel.  Can someone tell what bit rate would be required to encode
 > a standard colour TV brodcast channel?  How about monochrome?
 
      For NTSC colour video, a sampling rate (minimum) of 3 * Fsc (the
 colour subcarrier frequency) is required minimum to prevent chrominance
 cross-contamination.  The minimum accepted number of bits for broadcast
 quality composite video is 8 bits.  Hence, the data rate is 85.9091 megabits
 per second.
 
      Monochrome video still requires a sampling clock which is a harmonic
 of the horizontal scanning frequency (to prevent disturbances in straight
 vertical lines, etc) and typically, a rate of 8.4 mHz can be used with good
 results.  Of course, if one can tolerate reduced bandwidth video, even
 2.5 mHz is acceptable, with a sampling rate of 5 mHz.
 
      There are encoding schemes which reduce the number of bits required
 for real time NTSC digital video.  See this month's SMPTE Journal (JAN 87)
 for one such scheme.
 
 David Anthony
 DataSpan, Inc.


P.S. I might add that if one is willing to insert synchronizing words into
the data stream rather than encode the entire synchronizing pulse with data
at the same rate as the video, then a reduction in data rate of a little more
than 1/6 can be obtained....