|
This thread is confusing. Is your set an early 60s black and white set, or was 60s a typo?
1) An early 60s set would not have a 21 MHz IF. What do you have?
2) A black and white set might roll off the high frequencies, but would not have a specific trap for the color subcarrier, so it could have chroma dot crawl to some degree even if it's not full 4 Mhz bandwidth.
3) you seem to differentiate chroma dots and dot crawl. They are the same thing. The only difference is that in color sets with a subcarrier trap in the luma channel, the dots in large areas of the same color were eliminated, but dots still appeared on the left and right edges of colored objects. In later sets with a comb filter, depending on the design, color dots could appear inside the top edge and just below the bottom edge of colored objects, and were called "hanging dots." Sophisticated comb filter circuits included logic to switch in a chroma trap at these transitions. Fast motion could also fool the comb filter into letting dots through in some cases.
|