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El Duderino
Joined: 23 Jan 2011
Posts: 4653
Location: Portland, OR
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| Posted: Wed Feb 24, 2016 9:44 pm Post subject: |
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| mp20748 wrote: | | The multiburst pattern in comparison is a joke. |
I'm not sure I'd agree with that part. You have to use some reference stimulus signal to make measurements from, and a multiburst stimulus signal is one that is commonly used. I'd personally put more weight behind a good oscilloscope measurement of a multiburst signal than I would of a camera photo of a SMPTE pattern. YMMV.
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the dude
Joined: 11 Sep 2013
Posts: 179
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| Posted: Wed Feb 24, 2016 9:44 pm Post subject: |
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Our goal was to get an idea of where the weak point really is, and for this its just fine. Once you figure it out you can dig in deeper. I don't care if the amplitude for 1:1 is 0.2 db off at the driver when after the neckboard it is -3db on the screen.
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mp20748
Joined: 12 Sep 2006
Posts: 5689
Location: Maryland
TV/Projector: 9500LC Ultra / Super 02 and 03 VIM
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| Posted: Wed Feb 24, 2016 9:55 pm Post subject: |
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| El Duderino wrote: | | mp20748 wrote: | | The multiburst pattern in comparison is a joke. |
I'm not sure I'd agree with that part. You have to use some reference stimulus signal to make measurements from, and a multiburst stimulus signal is one that is commonly used. I'd personally put more weight behind a good oscilloscope measurement of a multiburst signal than I would of a camera photo of a SMPTE pattern. YMMV. |
So you have had good results getting good results with multiburst?
I used to use that until my visit to VDC back in 2005, and that is when I found out it's not a good source for proper measuring. And that was the same thing the application engineer at Intersil also told me.
Again, the SMPTE pattern is for Finals. That's after the video chain work. At least, that was the system Scott used, and the one I started using after my visit there.
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El Duderino
Joined: 23 Jan 2011
Posts: 4653
Location: Portland, OR
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| Posted: Wed Feb 24, 2016 10:08 pm Post subject: |
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| mp20748 wrote: | | So you have had good results getting good results with multiburst? |
As good as most any other reference stimulus signal I can use to make before and after measurements with, properly used. If it shows X Mhz is down Xdb, then so should a swept sine wave, or any of number of other stimulus signal used to measure frequency response and BW.
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redfox001
Joined: 16 Mar 2009
Posts: 2257
Location: The Netherlands
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| Posted: Wed Feb 24, 2016 10:17 pm Post subject: |
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| El Duderino wrote: |  |
Aaah I as wondering how to use that. Sory guys have to learn a lot.
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redfox001
Joined: 16 Mar 2009
Posts: 2257
Location: The Netherlands
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| Posted: Wed Feb 24, 2016 10:34 pm Post subject: |
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And it is very difficult to get a 100 MHz frequency generator. Mine goes to 20MHz.
Might be an idea to use a squarre wave from a fequency generator and inject it somewhere to see rise time? Gjaky measured bandwidth that way.
He we allready have the rise time so we could do some bandwidth calculations accounting for the probe of cause.
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mp20748
Joined: 12 Sep 2006
Posts: 5689
Location: Maryland
TV/Projector: 9500LC Ultra / Super 02 and 03 VIM
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| Posted: Wed Feb 24, 2016 10:37 pm Post subject: |
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| redfox001 wrote: |
Might be an idea to use a squarre wave from a fequency generator and inject it somewhere to see rise time? Gjaky measured bandwidth that way. |
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redfox001
Joined: 16 Mar 2009
Posts: 2257
Location: The Netherlands
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| Posted: Wed Feb 24, 2016 10:49 pm Post subject: |
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I get a whopping 76 MHz.
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redfox001
Joined: 16 Mar 2009
Posts: 2257
Location: The Netherlands
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| Posted: Wed Feb 24, 2016 10:52 pm Post subject: |
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150 Mega Mikes.
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redfox001
Joined: 16 Mar 2009
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Location: The Netherlands
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| Posted: Wed Feb 24, 2016 11:34 pm Post subject: |
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This risetime at several stages is something we could use to compare.
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redfox001
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redfox001
Joined: 16 Mar 2009
Posts: 2257
Location: The Netherlands
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| Posted: Thu Feb 25, 2016 1:14 am Post subject: |
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A way to measure bandwidth would be injecting a squarre wave and using a frequency analyser. My digital scope does a fourier transform.
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El Duderino
Joined: 23 Jan 2011
Posts: 4653
Location: Portland, OR
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| Posted: Thu Feb 25, 2016 6:34 am Post subject: |
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| redfox001 wrote: | | Aaah I as wondering how to use that. Sory guys have to learn a lot. |
Also, just to clairify, my comment about using two matched probing configurations wasn’t about making two measurements, per-say. When you invert one channel and sum it with the other, the resultant measurement isn’t ground referenced anymore, it's the difference seen by the two probe tips. Anything common to both probes (common mode) is nulled out. It’s the same technique used to measure the voltage across something that isn’t ground referenced.
Most of us who have used a scope have made the mistake of connecting the ground lead to a potential other than ground, at least once. 
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mp20748
Joined: 12 Sep 2006
Posts: 5689
Location: Maryland
TV/Projector: 9500LC Ultra / Super 02 and 03 VIM
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| Posted: Thu Feb 25, 2016 7:56 am Post subject: |
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| redfox001 wrote: | | A way to measure bandwidth would be injecting a squarre wave and using a frequency analyser. My digital scope does a fourier transform. |
In that case, why not a spectrum analyzer
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redfox001
Joined: 16 Mar 2009
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Location: The Netherlands
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| Posted: Thu Feb 25, 2016 7:58 am Post subject: |
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My velleman probe says hp9250 on the docs and has rise time of 1.4. That makes it 250MHz compatible. Just have to connect it better.
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redfox001
Joined: 16 Mar 2009
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Location: The Netherlands
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| Posted: Thu Feb 25, 2016 7:59 am Post subject: |
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| mp20748 wrote: | | redfox001 wrote: | | A way to measure bandwidth would be injecting a squarre wave and using a frequency analyser. My digital scope does a fourier transform. |
In that case, why not a spectrum analyzer |
Yes that is the same.
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redfox001
Joined: 16 Mar 2009
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| Posted: Thu Feb 25, 2016 8:10 am Post subject: |
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I guess with spectrum analysers we need good probes and high bandwidth equipment to?
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redfox001
Joined: 16 Mar 2009
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Location: The Netherlands
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| Posted: Thu Feb 25, 2016 8:14 am Post subject: |
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| El Duderino wrote: | | redfox001 wrote: | | Aaah I as wondering how to use that. Sory guys have to learn a lot. |
Also, just to clairify, my comment about using two matched probing configurations wasn’t about making two measurements, per-say. When you invert one channel and sum it with the other, the resultant measurement isn’t ground referenced anymore, it's the difference seen by the two probe tips. Anything common to both probes (common mode) is nulled out. It’s the same technique used to measure the voltage across something that isn’t ground referenced.
Most of us who have used a scope have made the mistake of connecting the ground lead to a potential other than ground, at least once. |
Ok I understand thanks for the warning. It would be nice if the scope had a memmory so I could use the same probe. The digital has another advantage here but you need both is what I read.
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mp20748
Joined: 12 Sep 2006
Posts: 5689
Location: Maryland
TV/Projector: 9500LC Ultra / Super 02 and 03 VIM
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| Posted: Thu Feb 25, 2016 8:22 am Post subject: |
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| redfox001 wrote: | | I guess with spectrum analysers we need good probes and high bandwidth equipment to? |
Well, that I wouldn't know. I've only used a pattern on my generator and had someone make me a pixel test pattern for my PC.
I guess anything is worth a try though, but when you find that square wave generator that's suitable for this let me know, because It's not easy using the pattern generator for this. And a 400mhz pulse generator is hard to come by.
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redfox001
Joined: 16 Mar 2009
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Location: The Netherlands
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| Posted: Thu Feb 25, 2016 9:17 am Post subject: |
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problem is using a 1080p@60 pattern will give you 75MHz or something like that at most. So if you give that to a spectrum analyser the limit will be the video resolution and not the equipment.
So how to set a vga card to get high frequency harmonics? Perhaps a pattern generator goes to 200MHz analogue bandwidth? That could work. So I do need a pattern generator for this. A PC dow not go so high in pixel resolution something like 2048x1536 that could give an analogue bandwidth of 100MHz or so but -3db etc.
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