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Old 26th February 2012, 12:12 AM   #1
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Join Date: Jun 2006
Default Help me get a handle on this RGB thing

I've been playing with some video circuits lately and I have to admit it's given me a headache. It's not that I can't find any information, it's just that I can't find any reliable information. It seems like when it comes to video, everyone's an expert but they all disagree

Anyway, here's what I wanted to know - I have a lot of old stuff, like laserdisc players, VTRs, video games and computers, etc... with SCART connectors or BNC jacks that output a System M analog RGB signal + composite sync or RGB + sync-on-green. Thing is, I've also got several new TVs that only have VGA inputs... I know how to separate sync from green and separate horizontal + vertical sync, so we'd have all of the same signals as VGA, but what about the other stuff like frequencies and voltage?

Here's what I know about NTSC-M:
525 lines (~480 for video)
Interlaced
30 frames per second
2 fields per frame
60 fields per second
Horizontal sync frequency: 15.734 kHz
Vertical Sync: 60Hz
Video = 0.7V pk-pk
White level = 1V
Black level = 0.3V
Sync level = 0V

Here's what I know about VGA:
525 lines (~480 for video)
60 fields per second
Horizontal Sync Frequency: 31.4684kHz <Exactly double the NTSC rate
Vertical Sync: 60Hz
Video = 0.7V pk-pk
Black level = 0.3V
Sync level = ? <Sources say negative, but is that really negative or just more negative than the video signal
Frame rate = ? <Is it 60 progressive frames or 30 interlaced frames?

So how do we get an NTSC-M picture to display on a VGA TV? Will it work if I just use an IC like the NJM2257 sync separator to split horizontal and vertical sync, or would I have to do something more like double the h-sync frequency or de-interlace it?

Sorry in advance if someone's already asked this, I just got so sick of searching for this and finding nothing but VGA-to-TV convertors and people who don't know the difference between frames and fields or RGB and those stupid "component" jacks they put on everything nowadays
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Old 26th February 2012, 08:30 AM   #2
dangus is offline dangus  Canada
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Join Date: May 2004
Location: Vancouver Island
When it comes to scan rates, there is no easy conversion. You have to capture the entire frame then spew it out at twice the rate. Boxes that did this for the benefit of folks with giant VGA monitors or data grade CRT projectors were called "line doublers" or "video scalers", and expensive. (Although these days you can find DVDO iScan doublers on eBay for around $50, with VGA output. They were the budget scaler in their day, a bargain at under $1000.) A minority of VGA monitors were compatible with standard definition scan rates, like the NEC Multisync II. TVM made a multisync knock-off which had an accessory, oddly called the "TV Mouse", which converted composite video to RGB. (This could be done with one chip (TDA3330?), as published in Radio-Electronics magazine, but the chip has long been obsolete.

About the cheapest way to convert from standard definition to VGA is to buy a tuner box from eBay or Dealextreme (or possibly the bargain table at a local computer dealer). Search ebay for LCD VGA TV tuner; about $30. Or (even cheaper) use a video (TV) capture card in a PC and run Dscaler.

The more practical but expensive solution is to "invest" in a nice A/V receiver, usually a 7.1 model, which has a built-in scaler that upconverts regular video to HDMI.
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Old 27th February 2012, 01:04 PM   #3
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Join Date: Jan 2008
Location: Virginia
1. VGA sync is "negative" in respect to signal polarity. That would be 0V if the black is at 0.3V. There is an option for "positive" sync - that would be at 1V.
2. VGA is 60p as opposed to NTSC 60i. You need a NTSC source that can convert to 480p (DVD players ca do that easy, not so much for LD).

What was said above is correct.
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