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Old 6th Mar 2005, 3:50 pm   #48
David_Robinson
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Join Date: Feb 2004
Location: Nottingham, UK
Posts: 94
Default Re: Multi-Channel VHF Modulator Design

Quote:
Originally Posted by flyback
... for a treat you could show us Test Card C.
Well I haven't got a full resolution copy of TCC so I hope TCF will do. I get big problems trying to take off screen photos - my camera keeps strobing out the interlace. After many attempts this is the best I can do.

http://homepage.ntlworld.com/david.r...20Card%20F.JPG

The whole picture is really interlaced, honest guv.
Quote:
what is on 6 music?
<off topic> Well it's all a matter of taste, but for me it's the station I've been waiting for. Of course you have to avoid the breakfast show (why do music channels feel the need for a show that's all talk?) but after 10am it's fab. None of that rap they have on Radio 1 (don't panic mods, I said RAP ).</off topic>
Quote:
I extended the blanking ...
Yeah I know, I said it wasn't finished...
Quote:
No takers for the 'don’t have a filter' idea then?
Seems not!
Quote:
Originally Posted by oldeurope
... you must look for sync level changes at the output of the vision demodulator in the TV set.
Of course it will have to be a set with proper gated AGC, to do the 0.25Hz test, none of that mean level AGC rubbish. Fortunately I have one such set. I have made the time constant on the base of the emitter follower nice and long, so the clamp is not presented with rapid changes in the sync tip voltage.

So how much white droop can we expect?

dV = I * dT / C

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

The result is attached with a 50Hz bar pattern from the Philips PM5570. As you can see any tilt on the white bar is negligible. I can't show you the 0.25Hz bounce test in a still photo, but I can tell you there was no problem
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Last edited by Dave Moll; 27th Jun 2007 at 10:26 pm. Reason: correct for username change in quote
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