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Old 6th Mar 2005, 9:01 pm   #49
oldeurope
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Join Date: Dec 2003
Location: Solingen, Germany
Posts: 727
Default Re: Multi-Channel VHF Modulator Design

Good evening David,
Your test card looks really very good

dV = 1A * 80.55s / 10nF = 8.1mV = 1.2% of (white - black) (worst case) (0.2% typical).

I am not satisfied with 10nF.
You have more than 100 grey steps in a picture so I don't think
this is acceptable.
In your oscilloscope picture I can see that the
white level goes a little bit down. At the beginning is
the marking line of your oscilloscope in the middle and at the end at the top.
I think 15nF will make it better. I have a test pattern on DVD which makes this mistake visible.


so the clamp is not presented with rapid changes in the sync tip voltage.

I don't understand it. Does this mean the sync tips run away from the
clamp level with rapid changes? Where did you measure this?

Kind regards
Darius
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