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redfox001
Joined: 16 Mar 2009
Posts: 2257
Location: The Netherlands
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| Posted: Sun Feb 21, 2016 4:36 pm Post subject: |
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I am sorry this is the one pixel 
A little disturbance
 Untitled by Radio Head, on Flickr
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the dude
Joined: 11 Sep 2013
Posts: 179
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| Posted: Sun Feb 21, 2016 4:38 pm Post subject: |
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Really good anyway!
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redfox001
Joined: 16 Mar 2009
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Location: The Netherlands
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| Posted: Sun Feb 21, 2016 4:38 pm Post subject: |
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| the dude wrote: | This looks pretty good!
Is this 470nH and a 1:1 pattern in the upper fields?
Huh, i really need to order some inductors ! |
I took the 470nH from an old driver from the high frequency peaking.
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redfox001
Joined: 16 Mar 2009
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Location: The Netherlands
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| Posted: Sun Feb 21, 2016 4:40 pm Post subject: |
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| the dude wrote: | | Really good anyway! |
I think this should be enough resolution to reveal low level detail in actual video.
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redfox001
Joined: 16 Mar 2009
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| Posted: Sun Feb 21, 2016 4:54 pm Post subject: |
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Making R bigger give a broader peak lower Q I think.
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redfox001
Joined: 16 Mar 2009
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| Posted: Sun Feb 21, 2016 4:58 pm Post subject: |
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By the way this is with standard neckboard just my high frequency peaking mod on the driver.
 Untitled by Radio Head, on Flickr
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redfox001
Joined: 16 Mar 2009
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| Posted: Sun Feb 21, 2016 5:00 pm Post subject: |
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And for comparing this was a lug tube in a 9518 low contrast. This is best ever. With mp vim.
 Untitled by Radio Head, on Flickr
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redfox001
Joined: 16 Mar 2009
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| Posted: Mon Feb 22, 2016 3:34 pm Post subject: |
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Valuable information here:
| CIR Engineering wrote: | A peaking circuit is used to add "pre-emphasis" to the video signal. Pre-emphais is kind of like increasing the sharpness where sharpness in this case is artifically amplifying the frequency of the video signal.
This is also refered to as "preshoot" and "overshoot." If you look at a white window on an oscilloscope, when you add peaking you will see that the point of transistion between black to white has a peak (amplified response). Here is a photo of extra peaking as shown on an oscilloscope.
What this looks like on the screen of a projector is that the transistion from black to white will show a shadow or slight ghosting of the black onto the white. You can observe this on almost any analog TV (or even many digital TVs) by putting up a white window (or sharpness test pattern) and increasing the sharpness. The left side of the white window will get highlighted and will "ring."
Every component (each IC, trace, etc) in the video chain will cause some attenuation to the amplitude of the frequency response. Peaking is used to add extra amplitude to help reduce the attenutaion of the amplitude. Too much peaking results in ringing, but just the right amopunt of peaking will help preserve the original frequency response of the video signal for when it is passed to the next component in the chain. This makes the image on screen appear sharper without negative side effects.
You may not even have a peaking circuit on the IC you are changing, I have not looked. But it is a comon place to have a peaking circuit in the video chain so it's worth checking into. Also, you may discover that the peaking circuit is already optimized even after changing the IC.
Good luck!
craigr |
http://www.curtpalme.com/forum/viewtopic.php?p=358664&highlight=peaking#358664
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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: Tue Feb 23, 2016 9:12 am Post subject: |
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| redfox001 wrote: | | This does remind me of him saying that he changed the resistor between the top and the bottom halve on the marquee (R95). He said it was a kind of crossover distortion that he corrected. It allways made me wonder a crossover distortion there? Think he did not get it but I am no expert either. |
What the hell are you talking about here, and why do you keep posting really dumb stuff and attributing it to me. In no way would I have said such about that resistor. I understand fully what its purpose is and can very well explain its purpose.
crossover distortion..
Also and while I'm at it. Let me also get back to you and the theorist supporting your claim that by me removing the ARC diodes from those Motorola RF transistors that is why you had two transistors fail...
Remember that I said They were RF Power transistors and I had referenced my military radio days and experience and training. I also supported and backed it all up by saying I've been doing this for over ten years, with you being maybe the only case where this was assumed or where there was transistor failure.
Now I must say there have been a few cases where there has been transistor failure, but these particular failures were directly related to the CRT Ground wire (touching when either installing or removing a neck board) discharging on the neck board. This happens often, and even as much as I'm aware of this, it still happens to me.
However, the failure rate is so low that I would say it happens only 2% of the time. But in the case where I have had a reported failure (and it was few), when I asked "Did the ground wire arc the board?" I was told YES!
Ok, here is why that DIODE is NOT needed on those RF Power Transistors:
It's really simple, they are RF Power Transistors..remember me also mentioning “antenna circuits” and maybe even a little more on RF design. The thing that's needed understanding on is:
“FORWARD AND REFLECTIVE POWER IN RF TRANSMISSION”
What that means is that in RF power final stages, there is a danger of what is also known as “Reflective Power” there is also ratios and measurements that deal directly with this. And believe it or not, Reflective Powers can take out an RF final stage if the numbers are off, or if things are not properly matched. So when damage happens, the first thing to go would be the final stage, which almost 100% of the time would be the final transistor or transistors. And if you read in the links below, you'll see that no antenna system or transmission line is 100% immune from not being perfectly matched at all times. So what needed to happen to keep transmitters from Not failing all the times was the way they designed the power device to decrease or eliminate this problem. Well with me already knowing this, to include knowing the difference between the amount of the reflective power into the RF device, compared to the amount and potential of the ARC from the CRT, my thought was why would those diodes be necessary or needed when the RF device itself could handle maybe hundreds of times more shock than what kicks out of those tubes. And to further prove my point on these RF Power transistors as many who has also worked on these Marquees would know, that CRT ground wire has arced a many board and they still worked.
But lets go further. VDC has a newer neck board that's NOT using the Motorola's but Sanyo transistors instead. If that CRT ground wire ARCs that board anywhere on it, you will have to replace one or more of those Sanyo's. So far, I've replaced about 11 of those Sanyo transistors on the newer neck boards. And check this out, the diodes are in place on the newer neck boards and they still FAIL. So what is going on there, why are the Sanyo transistors still failing with the diodes... Hmmm, not sure, but what I do know is and this is from experience, those diodes don't always work and when using transistors that were designed for RF circuits where much higher and more aggressive voltages exist, the diode is not needed, therefore allowing for lower capacitance and higher bandwidth performance on the neck boards.
So how do you question someone on something using non-relevant theory, when they have proven results and have so far achieved something that not even the manufacturers were able to achieve. Has it really sunk in that maybe I'm to only person you know that has been able to get a video chain in a CRT projector to exceed 300Mhz bandwidth? And so far, who else has also been able to prove they have done such, or been able to even get 1080P properly resolved in a video chain, other than maybe Scott at VDC...yet I don't know what I'm doing..
FORWARD AND REFLECTIVE POWER IN RF TRANSMISSION
Reverse or Reflected Power Protection
We have seen that excessive power reflected back from the load into the transmitter could damage it. The best way to avoid damage is to have a good match of course. In doing so, not only we reduce the risk of damage, but we also optimize the power transfer and minimize power loss.
It is not always possible to guaranty a good match under all operating conditions. It could be that the load VSWR is not well controlled, or that the system has to operate over a broad frequency range, because it is more difficult to ensure a good match across a broad frequency range than over a narrow frequency range.
An example of condition which could cause an otherwise well matched antenna to show high VSWR would be the presence of an obstacle in front of the antenna, reflecting some of the signal back to the transmitter. Other potentially damaging conditions include damage to the transmission line between the transmitter and the antenna, such as a coaxial cable cut or pinched, or water intrusion inside the cable.
http://www.ko4bb.com/e102/e102-10.php
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https://en.wikipedia.org/wiki/Standing_wave_ratio
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The forward power is the amount of power going to a termination point. The reflected power is the amount of power returning from the termination point. The perfect set up is a 100% forward power and 0% return power. If you are using a power meter with a Forward and reverse reading system, you would see a VSWR of 1 to 1. In the real world this does not happen as there is not avalable a perfect termination, but we try to get a close as possible.
http://www.eham.net/ehamforum/smf/index.php?topic=72438.0
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https://www.antennex.com/preview/vswr.htm
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redfox001
Joined: 16 Mar 2009
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Location: The Netherlands
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| Posted: Tue Feb 23, 2016 11:53 am Post subject: |
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Moght very well be an arc I just did not see an arc but I do not care why the board failed. It is more interesting to use the info that it gave us in how these boards work. About crossover distortion I remember you said something that is was LIKE crossover distortion in an audio amplifier. If I find it back I will post. Usually my memmory still serves me well but understanding all the things said is not so easy  No need to go to war on this I was just teasing a bit. Thanks for the info. How a fox gets a peace of cheese these days 
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Last edited by redfox001 on Tue Feb 23, 2016 12:21 pm; edited 1 time in total
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redfox001
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redfox001
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| Posted: Tue Feb 23, 2016 12:29 pm Post subject: |
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Datasheet says sa1539/sc3954 sc3953 500 MHz 120V
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redfox001
Joined: 16 Mar 2009
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| Posted: Tue Feb 23, 2016 12:34 pm Post subject: |
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I think the first will work with 180V barco supply rail.
I also found that lowering the supply makes it nessesary to rise the g2 and that makes for less punch acording to Scott. I wonder if that explains why the 170V on the marquee looks a bit dimm compared to barco?
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redfox001
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the dude
Joined: 11 Sep 2013
Posts: 179
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| Posted: Tue Feb 23, 2016 6:20 pm Post subject: |
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| Quote: | | Has it really sunk in that maybe I'm to only person you know that has been able to get a video chain in a CRT projector to exceed 300Mhz bandwidth? |
Maybe you are the only person in this business who can't tell frequency from samplerate 
You mean 300 Mhz pixel clock?
You should stop this stupid advertisement, thats ridiculous...
And no, that is not a matter of definition. The term "bandwidth" and "sample rate" are well defined. Call your fantasy unit Megamike if you like, buts thats not Megahertz.
https://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem
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the dude
Joined: 11 Sep 2013
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| Posted: Tue Feb 23, 2016 6:32 pm Post subject: |
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And of course discussions on SWR related problems with power transistors are interesting for ham radio and have nothing to do with esd or overvoltage protection.
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the dude
Joined: 11 Sep 2013
Posts: 179
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| Posted: Tue Feb 23, 2016 6:43 pm Post subject: |
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And now something constructive:
We can use HSMP-3832-BLKG for the protection clamp. Its a pin diode (2 diodes in single package) capable of 200V reverse voltage each.
It has only 0,3 pf capacitance per device. At 20V reverse voltage it would only be 0,2 pf!
The diode is available from farnell.
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the dude
Joined: 11 Sep 2013
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| Posted: Tue Feb 23, 2016 8:12 pm Post subject: |
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Maybe a pin diode is not well suited. They have ultra low capacitance, but high resistance on high frequencies, wich maybe include transients. Not sure, normally they are used for RF signal switches.
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redfox001
Joined: 16 Mar 2009
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| Posted: Tue Feb 23, 2016 8:20 pm Post subject: |
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I have been playing with my new Tektronix. First I need a way to get the sync signal from the moome because I can not get a good trigger from the video signal a lot of noise is coming along. I measured direct from the moome only for now.
Some simple observations. Boy this scope works good to get to see what is happening. One pixel patterns turn out to be correct sinus patters. They should and all those digitals make them square on your screen. Good to see this for real.
But the two and three pixel patterns should be more square. Because of the bandwidth the higher harmonics of those squares are filtered away that explains the wave. What I find strange is that the top looks different from the bottom. I played with probe compensation. Different ways to measure with ground wires but still this asymmetric pattern direct from the moome why is that?
 Untitled by Radio Head, on Flickr
 Untitled by Radio Head, on Flickr
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Last edited by redfox001 on Tue Feb 23, 2016 8:36 pm; edited 1 time in total
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redfox001
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| Posted: Tue Feb 23, 2016 8:32 pm Post subject: |
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I think the videodac can only make a sine from 1 pixel patterns and make the wavy pattern from three pixel patterns. That should be correct. Asymmetry is still strange.
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