Testing a Video Signal
in [Design]
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From: Mike Warren on 20 Jan 2010 23:20 Phil Allison wrote: >** Guess that proves the point about the colour burst frequency being off >- >beyond all possible doubt. Yes. >Tweaking the PCI card's crystal was suggested by ME to YOU just over >THREE >days ago. > >Rub, rub rub ..... LOL! :-) -- - Mike
From: JosephKK on 21 Jan 2010 02:54 On Mon, 18 Jan 2010 02:14:05 +0000 (UTC), "Mike Warren" <miwa-not-this-bit(a)or-this-csas.net.au> wrote: >We have just purchased a quantity of PCIe video cards with >TV out (S-Video) and can only get a monochrome picture >from the S-Video output. > >I have so far tried 6 different cards from 2 batches and >all have the same fault. Here are my observations?: > >-Another brand of video card that used the same video chip >(nVidia 8400GS) works fine using the same driver. > >-The driver /is/ set up correctly. > >- The fault is there in both PAL and NTSC modes. Only one >of my monitors supports NTSC so I haven't done any extensive >testing in that mode. > >-These cards produce a B&W picture on 3 separate monitors >(2 LCD and one CRT) All monitors work fine with the other >brand. The 15 year old CRT monitor will produce a colour >picture from this card for a few seconds when cold. > >- Feeding the signal into a Canopus ADVC-100 video capture >device produces a colour picture on my computer. > >Here are some pictures of the output. In the oscilloscope >pictures the top trace is the composite signal after my >passive S-Video to composite converter (just a 1000pF cap) >and the bottom trace is the chroma signal from the card. >www.mike-warren.net/tmp/DSO1-ECS-web.jpg >www.mike-warren.net/tmp/DSO1-Leadtek-web.jpg >www.mike-warren.net/tmp/TV-ECS-web.jpg >www.mike-warren.net/tmp/TV-Leadtek-web.jpg > >This is a vectorscope signal produced using Adobe Premier >from the same colour bar signal. I haven't recorded the >output of the good card since I don't believe the >vectorscope will help with this problem. >www.mike-warren.net/tmp/Vectorscope-Leadtek.jpg > >What tests can I do to try and work out what is wrong with >the signal? I tried to read the frequency of the colour >burst but I haven't been able to lock the DSO (Tek TDS1002) >on it so far. > >The supplier claims there is nothing wrong with their cards >as no one else has ever complained. Simply looking at the 4 scope traces is it clear that the cards do not seem to produce proper PAL "phase alternate line" signals. In particular the "cheaper?" cards may not bother to invert the chroma burst as would be needed to maintain proper chroma.
From: JosephKK on 21 Jan 2010 02:57 On Tue, 19 Jan 2010 14:38:11 -0800 (PST), Mark <makolber(a)yahoo.com> wrote: > >> ** The OP is in Australia an so using PAL monitors. >> >> Another trick is to take a known good video >> signal and loosly couple the UUT video to it and you will see the >> video sync drift through. If the H sync drift less then 1 frame per >> sec or so, it is probably close enought that a monitor should lock to >> it. >> >> ** Horizontal synch is NOT the problem. >> >> Colour sub carrier synch IS !! >> >> ..... Phil > >Phil, > >yes agreed, but since Hsynch and subcarrier bust are phase locked to >each other, the error expressed in % should be the same for both. So >if the H synch is very close to correct, the color burst should also >be very close to correct.. > >Mark Assumption unjustified. PAL is seriously different from NTSC.
From: JosephKK on 21 Jan 2010 03:54 On Mon, 18 Jan 2010 23:06:33 -0700, "bg" <bg(a)nospam.com> wrote: > >Phil Allison wrote in message <7rk966Fnf0U1(a)mid.individual.net>... >> >>"bg" >> >>> If the frequency of the burst was off, the color hue would shift, but you >>> would still have color. >> >>** Completely WRONG. >> >>The phase of the colour sub carrier is what produces hue shifts. >> >>Explains why NTSC is so prone to hue shifts in transmission and why PAL was >>invented to solve the problem. >> >>If the TV receiver or monitor cannot phase lock onto the sub carrier burst, >>then normally no colour will appear. >> >> >> >>.... Phil > >If the frequency was off but close enough to allow the oscillator to >partially lock to it, wouldn't that cause the hue to alternate? > I don't happen to have the standards to reference, but i seem to remember that the receiver / display specifications required a much larger lock-in range than is allowed for broadcast chroma carrier variations. Of course computer display cards have much more variation than broadcast transmissions.
From: Mark on 21 Jan 2010 12:52
On Jan 21, 2:57 am, "JosephKK"<quiettechb...(a)yahoo.com> wrote: > On Tue, 19 Jan 2010 14:38:11 -0800 (PST), Mark <makol...(a)yahoo.com> wrote: > > >> ** The OP is in Australia an so using PAL monitors. > > >> Another trick is to take a known good video > >> signal and loosly couple the UUT video to it and you will see the > >> video sync drift through. If the H sync drift less then 1 frame per > >> sec or so, it is probably close enought that a monitor should lock to > >> it. > > >> ** Horizontal synch is NOT the problem. > > >> Colour sub carrier synch IS !! > > >> ..... Phil > > >Phil, > > >yes agreed, but since Hsynch and subcarrier bust are phase locked to > >each other, the error expressed in % should be the same for both. So > >if the H synch is very close to correct, the color burst should also > >be very close to correct.. > > >Mark > > Assumption unjustified. PAL is seriously different from NTSC.- Hide quoted text - > > - Show quoted text - I see here http://www.videointerchange.com/pal_secam_conversions.htm that the 3 NTSC frequencies are related and phas elocked as I said...... but that for PAL the three frequencies are also related EXCEPT that they added a 25 Hz offset to the burst freq... thanks for pointing that out.. Mark |