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H refers to the horizontal line period.
Your first two traces show start of switching pulse exactly 6.5H before vertical sync. The third trace shows 7.5 H. This should not be a terrible problem, it just means the switching transient is slightly higher above the bottom of the active picture than specified (by one half a horizontal line).
[EDIT - I think this could vary if the recording machine for the tape was slightly off.]
A noise spike at the switching instant is probably normal.
I'm not following which big pulses you are referring to, and do you mean truncated amplitude or time? Can you post an image with a pointer to what you mean? Are you referring to the last few lines of active video, which vary with picture content?
In any case, this proves that the switching transient is not what you are seeing one third of the way down the picture.
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Last edited by old_tv_nut; 03-30-2022 at 10:22 PM.
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