Quote:
Originally Posted by Robert Grant
One thing I notice after 39 years of watching NTSC color:
When my parents got our RCA CTC-38 (1969), the color was usually good at one "right" hue (phase) setting, yet it was not very uncommon (especially on videotaped network programming) for the phase to be far off the mark (green or purple faces, blue grass). Sometimes the local station would super a notice "technical difficulties" at the bottom. I understand this was because the NTSC reference signal ("back porch", "color burst") could not be transmitted with the picture on the microwave links then in use by networks (please, someone, tell me WHY this was so, if they can send a chartreuse dress image on the link, they can send the burst, can't they ?).
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The burst was and is always transmitted with an analog signal. It must be, otherwise there is no color frequency and phase reference. However, it has been the practice frmm the beginning to generate a new, clean synchronizing and burst signal locked to the incoming signal. Early in the color days, there was often considerable degradation of the video and the burst, so when the burst was regenerated, sometimes it was the wrong phase. (Sometimes this was simply because no-one adjusted it correctly.) Since there might be more than one stage of regeneration, it could be very difficult to track down the stages at which something went wrong.
For a short time, a signal called VIR (vertical interval reference) was implemented. The idea was that this auxiliary burst would be inserted at the studio and not adjusted or replaced along the network. Some TV sets (General Electric in particular) used the VIR to make automatic color adjustments. However, broadcasters discovered that they could use the VIR to adjust the signal and even automatically compensate any transmitter shortcomings. At that point, the VIR was being adjusted and no longer represented the original studio signal. Eventually, the industry gave up on the whole idea.
Improvements were made in the networks over the years. At one time, the networks adopted atomic clocks to set the burst frequency, and the local stations then locked to that. Later, when frame synchronizers became available, the local stations could re-sync all incoming signals to their local reference.
Another big improvment was simply the move to solid state gear, which could go much longer than tube gear without drifting out of specification.
These days, with much video being originated in digital components, or at least converted to digital before going over the network, there are fewer points at which it is critical to carry the burst properly.