Testing a Video Signal
in [Design]
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From: Phil Allison on 20 Jan 2010 17:30 "Mike Warren" > I was able to get lock on the colour burst and measure it with the > cursors on the Tek. I get 4.44MHz on the good card and 4.42MHz on the > bad ones. Unfortunately this is only a one step difference of the > cursor position so is not an accurate indication. ** You bet is not accurate enough. As I alluded to before, the lock-in range of typical PAL TVs and monitors is only as far as the internal 4.43MHz crystal can be pulled by a small amount of capacitance - ie maybe +/- 25 Hz. According to your testing, a CRT monitor locked briefly when it was cold - so the sub carrier burst is likely to be on the low side of the correct frequency. The only way to measure it is to tweak a monitor's crystal so it DOES lock - then measure the frequency of oscillation with a counter. ...... Phil
From: Mike Warren on 20 Jan 2010 18:23 Jan Panteltje wrote: >Wonder what a 'theoretical technique' is, about the same as your S-video >interface technique? You tell me. How would you do it? >Do you not think that before complaining about a thing you at least should >connect it in the correct way? Again, I did. I connected the S-Video output from the card to the S-Video input of the monitor using a commercial S-Video cable and got a monochrome picture. From all six cards under test. The other brand, and others before that, work fine. >Here analog video is long of the past, only some very small cameras I >have still use it. Here too, and this is causing me problems because video cards with S-Video or composite outputs are nearly impossible to find now. However my customers have large numbers of old TVs installed in various venues. It would bankrupt them to have to replace all of them and the wiring etc. to get HDMI. And absolutely no one involved would care about the improvement in quality. I'm on the lookout for HDMI to S-Video or composite converters, but it seems no one makes one. >To measure the frequency difference you can put one signal on X and >and one on Y. >A Lissajous figure will appear that rotates the faster the bigger the >difference. I only have 10 cycles to view. If I had both cards running simultaneously I still wouldn't be able to sync the colour bursts to do that. >Or you could external trigger on one, and measure the other, and see >how many periods pass by in a second. >If there is a lot of difference that would be difficult. See above. >Here is a cheap frequency meter, but the resolution is only 32 Hz: >Should be enough for this purpose. I have one that is accurate to within a few Hz too. The problem is getting it to read the burst. The only way I can see to do that is the way Phil suggests and measure it at the monitor's oscillator. That's more work than I want to go to at this stage, unless the manufacturer comes back to me and says there is no problem. Then, I will need to offer proof. >>I could discern no difference in the timing of the H-sync between >>the 2 cards. > >H sync frequency has nothing to do with it. I know. I just did this to answer the suggestions of a couple of posters. >>The chroma level is within the measurement error of my Tek between >>the 2 cards as well. > >Tek?? Oh well. Do you seriously think that a monitor will have trouble with a chroma /level/ variation of a few percent? I get that you don't like Tek, and I'm not all that impressed with them either, but I don't have the budget others do, especially if this is to help correct someone else's error. All I needed to do here was connect the card to my monitor via the S-Video connector and tell the manufacturer that it didn't work. What I wanted to do was get a little more information as long as it didn't entail too much work so I could reduce some of the inevitable to and fro while the manufacturer tried to tell me things like "Make sure you have the card set to PAL, not NTSC" and "have you tried another cable". -- - Mike
From: Mike Warren on 20 Jan 2010 18:25 Phil Allison wrote: >The only way to measure it is to tweak a monitor's crystal so it DOES lock > - >then measure the frequency of oscillation with a counter. Clearing enough space to disassemble the monitor is more work than I want to do unless I have to, so I'll wait and see what Leadtek have to say first. :-) -- - Mike
From: Jan Panteltje on 20 Jan 2010 18:48 On a sunny day (Wed, 20 Jan 2010 23:23:03 +0000 (UTC)) it happened "Mike Warren" <miwa-not-this-bit(a)or-this-csas.net.au> wrote in <xn0gpehuj4cjpf002(a)news.aioe.org>: >Jan Panteltje wrote: > >>Wonder what a 'theoretical technique' is, about the same as your S-video >>interface technique? > >You tell me. How would you do it? I would have to charge you, and, as you are so poor, you would not be able to pay. But there are a lot of examples on the web. Google is your friend.
From: Phil Allison on 20 Jan 2010 18:59
"Mike Warren" Phil Allison wrote: > >>The only way to measure it is to tweak a monitor's crystal so it DOES >>lock - >>then measure the frequency of oscillation with a counter. > > Clearing enough space to disassemble the monitor is more work than I want > to > do unless I have to, ** You mis-comprehend. I am NOT telling you what you to do - only pointing out what measurement method would likely work. > so I'll wait and see what Leadtek have to say first. ** You already have your evidence. The PCI video cards do not work with the monitors you need them to work with. Therefore, they are " unfit for the purpose intended " as the TPA says. Even if you had a figure for the burst frequency error - it would not prove you case any better than the evidence of people's eyes. ..... Phil |