LukeEvansSimon wrote:
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R=Attribute&Value&Explanation
R=RGB Drive Amp Bandwidth&9.6Mhz&RGB cathodes need to be varied 666 times per line from peak voltage for black to trough voltage for white, corresponding to 666 black and white dot pairs, 240 lines per frame, 60 frames per second
This does not take into account blanking time. One horizontal line of NTSC is 63.5uS, but only 52.6uS of that is active video. Furthermore, the vertical overscan and blanking area is quite large: 525/2 - 240 = 22.5 lines per 60Hz refresh.
52.6 x 0.75 = 39.45uS
1000 / 39.45 = ~25MHz minimum frequency response for 1000 TVL at 15KHz horizontal refresh. This adds up, by the way: Common pixel clock frequencies in 240p game systems are 5-7MHz. Saturn high-res mode is 14.3MHz, which is the highest clock pre-Dreamcast and is 704 pixels across per line.
Depending on the TV, you may encounter bottlenecks to this well in advance of the main drive transistors. Some may even employ lowpass filtering to get rid of unwanted high frequency noise. Heck, if the AC coupling capacitors in your transmission lines are only aluminum electrolytics without anything else in parallel, they probably won't pass 25MHz undistorted.
But this is all pretty academic.
LukeEvensSimon, I do have to give you credit. You saw potential, formed a theory, tested a design, and got results.
I'll also say that you were 100% right when you said that TVL is a function of the whole system and not just the size and density of phosphor triads on the face of the display. I think I can say that many of us, including myself, had been mistakenly assuming that dot-pitch was virtually the exclusive factor in determining TVL, while we can now understand more fully how big a role spot size plays.
If a person has a display with the abundance of phosphor triads in the CRT necessary to make this mod work, then it could be worth a look for them. If they prefer the result, good for them, and you've done them a service. For all of this, we owe you thanks.
Having said that, I think that part of the reason why some people still balk at this whole thing is that a phrase like "double the TVL" sets certain expectations. Not being able to see your modded display in person, I can only imagine how it really comes across, but your SOTN before/after shot doesn't look anything like the Mega Man X3 shots from your original OP that you used to illustrate the mod's potential. Upon closer inspection, the high-TVL MMX3 shot still has the beam hitting multiple phosphor triads horizontally and vertically for every pixel. This goes against your premise that a game image can be pleasingly resolved with only one triad per pixel.
When I look at the shots I posted compared to your before/after, the overall impression I get is that dot-pitch is still the dominant factor determining how a CRT looks, assuming all bandwidth requirements are being met. You might succeed in doubling TVL in some strict technical sense, but the result almost certainly isn't going to look like how a quality high-TVL screen would look, and that's why some people find the title of your thread misleading. At the moment, it looks like a more realistic expectation to set, in terms of the
upgrade in appearance to the user, would be something like +100 TVL. That and skinnier scanlines for those who are into that sort of thing.
As you've observed, it's a bit silly to fixate on the highest TVL for its own sake when the vast majority of 240p gaming falls within 480 TVL (I'd say even 384 TVL, or 512 pixels per line). Much to the contrary, my personal takeaway from this is that I ought to turn
down the focus on my 900 TVL monitor, which was seemingly designed with small spot-size for its HD capabilities (which I hardly ever use). Anyway, I think you'll see more enthusiasm for this mod if you recast it as potentially removing critical bottlenecks, and set aside hitting sky-high technical benchmarks. 350 and 450 TVL sets sit right before the boundaries needed to resolve certain "high-res" 240p games; you've got a mod that might convincingly get them beyond those boundaries. That, to me, is exciting.
Just my two cents.