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I'm setting up my new HTPC drive my Sony D50 projector, and am trying to understand the projector's capabilities so as to optimise PowerStrip settings. I could use some help.


I've searched through this site to learn what I can but I'm getting a little confused. I can see how Total Horizontal pixel count (including front porch etc) x Total Vertical pixel count x Vertical refresh rate = pixel clock.


For example my current res is 1024 (1312 total) x 768 (800 total) x 75Hz = 78.7 MHz pixel clock.


However I've read on this site that as a pixel is generated on the rise and fall of the clock then the required bandwidth is only half this amount, only 39.35 MHZ. But the numbers don't seem to stack up in practice.


My projector bandwidth spec is 75MHz, which I can't correlate to it's resolution limit of 1280x1024x60Hz. And if it can produce that resolution then you would expect it to run 1024x768 at somewhere around 100Hz, yet my projector complains at anything more than 75Hz.


If anyone could enlighten me a little further I would appreciate it. Optimised PowerStrip settings for PAL and NTSC etc to get the best out of a projector of this capability would also be welcome:D
 

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Hey No.4, here's the 411 on bandwidth (sorry, couldn't resist).

You've just about got the bandwidth as it relates to the resolution and refresh rate. The pixel clock is right, and the pixels only change at half that rate. However, that's not necessarily the bandwidth required. It's going to be more than half. Remember that pixels are changing at discreet points in time, on the rising edge of the pixel clock to be precise, so we're talking about square waves and not sine waves which is more natural when you discuss bandwidth. It takes a LOT more bandwidth to faithfully reproduce the rising and falling edges of a square wave, even if the frequency of the square wave is slow.


Secondly, you can forget all of that anyway. What matters is that you don't exceed the projectors H and V sync capabilities. What's the maximum horizontal sync frequency the D50 can take? As long as you stay under that, you're ok.


What happens if you input a signal that requires more bandwidth to resolve than your projector is capable of but you are still within the sync capabilities? It just won't fully reslove the pixels and you'll lose some detail, that's all, no harm done.


Cary
 

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And while all of what Cary says is true, the real limiting factor on these analog CRT's is going to be the Spot size vs the tube area. This is what will determine if you have overlap on the scan lines which will soften the picture as you move up in resolution (frequency). My guess is that the D50 is going to be somewhere between 600P and 720P for the sweet spot. Anything higher, overlap, anything lower, scan lines.


Terry
 
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