Quote:
Originally Posted by dtvmcdonald
...It a compormise between the best looking Q channel response and the problem that the best response looks terrible because its much too early ... it would need less delay in the Y delay line and the I filter, which has intentional delay in it . I have actual photos of the restult on +-I and +-Q bars posted on an earlier thread here. I will repost here. Note that the time error is obvious here ... but not on program material. Note that there is an orange bar from crosstalk on green to violet but the corresponding bar on green to violet looks more like luminance. Except for the black and white bars, Y is constant. Note that th I channel looks really good.
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If by Q "best response" you mean sharpest transition, then that may correspond to wider than normal Q bandwidth and the early Q timing you have. This will result in some quadrature crosstalk of I into Q, which I think is part of what you see in the yellower left edge of the green in the violet to green transition, and the bluer left edge of the violet in the green to violet transition.
Of course, this could be confused by the presence of a slight ringing in the Q circuit response - if you see a ringing transition, it's hard to separate the Q baseband response from quadrature distortion. To separate things, you need to input a step waveform at the Q demodulator output and see that it's not ringing at the CRT.
Also, there's a question whether the chroma in the test source has wideband I and narrowband Q or is equiband.