Splitting sync-on-green video signal
in [Design]
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From: a7yvm109gf5d1 on 10 Jan 2010 01:06 On Jan 10, 12:51 am, mike3 <mike4...(a)yahoo.com> wrote: > As I've heard if you try and send a green with sync on green in it > through a monitor that doesn't support it, it'll fill the screen with > lots of green hue, or the monitor might not work right, etc. That would make sense since having a sync means the entire black level relationship is blown if the monitor expects a 0V reference. It's weird since the Amiga 1950 monitor supports SOG but now that I think about it there was a switch somewhere on the thing to select for that mode.
From: Glenn Gundlach on 10 Jan 2010 01:12 On Jan 9, 9:38 pm, mike3 <mike4...(a)yahoo.com> wrote: > On Jan 9, 10:16 pm, a7yvm109gf...(a)netzero.com wrote: > > > On Jan 9, 5:09 pm, mike3 <mike4...(a)yahoo.com> wrote: > > > > Hmm. But how about not only extracting the sync but also removing > > > it from the green line to get a pure green signal? In other words, > > > have > > > something where the input is the green+sync, the outputs horizontal > > > and vertical sync and also pure green component (no sync)? > > > Clamp the black level and subtract it from the video, this will bring > > the video down by the 0.3V (IIRC) of the usual black level, but like > > John said, why? > > It makes the circuit complex and you don't see the syncs anyways so > > why remove them? > > Because I need to use this with monitors that do not support sync on > green. None of the monitors I have are listed as supporting sync on > green, and I think there aren't many models of monitors that actually > do, > are there? I've got an HNC AH191A monitor and Acer X223W, neither > of which ring up anything when searching for them plus "sync on green" > on Google. I don't want to get rid of the sync, just split it off into > separate > lines, like the monitor requires, and send it a pure green signal down > its > green port, as it requires. That is, to make a thingy that takes in > the > combined green+sync signal in one end and yields horizontal, vertical, > and pure green component signals out the other. You'll nead something like the LM1881, a DC restore amplifier to assure the DC levels and then a 'clamp amp' (clipper) to remove the sync currently on the green. The Analog Devices AD8036 is the best clamp amp I ever used and would remove anything below the threshold level and drive the coax dierctly. It isn't terribly difficult but also not trivial. You'll also need 2 gain of 2 line drivers to distribute the red and blue. Mis-terminated analog video looks very bad. G²
From: Glenn Gundlach on 10 Jan 2010 01:14 On Jan 9, 9:58 pm, a7yvm109gf...(a)netzero.com wrote: > On Jan 10, 12:38 am, mike3 <mike4...(a)yahoo.com> wrote: > > > > > > > On Jan 9, 10:16 pm, a7yvm109gf...(a)netzero.com wrote: > > > > On Jan 9, 5:09 pm, mike3 <mike4...(a)yahoo.com> wrote: > > > > > Hmm. But how about not only extracting the sync but also removing > > > > it from the green line to get a pure green signal? In other words, > > > > have > > > > something where the input is the green+sync, the outputs horizontal > > > > and vertical sync and also pure green component (no sync)? > > > > Clamp the black level and subtract it from the video, this will bring > > > the video down by the 0.3V (IIRC) of the usual black level, but like > > > John said, why? > > > It makes the circuit complex and you don't see the syncs anyways so > > > why remove them? > > > Because I need to use this with monitors that do not support sync on > > green. None of the monitors I have are listed as supporting sync on > > green, and I think there aren't many models of monitors that actually > > do, > > are there? I've got an HNC AH191A monitor and Acer X223W, neither > > of which ring up anything when searching for them plus "sync on green" > > on Google. I don't want to get rid of the sync, just split it off into > > separate > > lines, like the monitor requires, and send it a pure green signal down > > its > > green port, as it requires. That is, to make a thingy that takes in > > the > > combined green+sync signal in one end and yields horizontal, vertical, > > and pure green component signals out the other. > > I'm no expert on monitors, the last time I played with S.O.G. was with > an Amiga and a Commodore 1950 monitor... > Gives you an idea of the time frame. > > I don't think a monitor would care if there are syncs or not on the > green. I think the "not supported" means the monitor can't extract > syncs from green (cost cutting), not that it will harm the monitor. > > However you could look for an Extron box called a 118 on eBay, for > about 20$ it does all this stuff for you. > 20$ or days of fudging around... You choose! > > www.extron.com/download/files/userman/rgb118series-man.pdf It depends on the specific monitor. Different models from the same manufacturer may behave differently. Better to clip off the sync but more expensive. G²
From: a7yvm109gf5d1 on 10 Jan 2010 02:19 On Jan 10, 1:06 am, a7yvm109gf...(a)netzero.com wrote: > On Jan 10, 12:51 am, mike3 <mike4...(a)yahoo.com> wrote: > > > As I've heard if you try and send a green with sync on green in it > > through a monitor that doesn't support it, it'll fill the screen with > > lots of green hue, or the monitor might not work right, etc. > > That would make sense since having a sync means the entire black level > relationship is blown if the monitor expects a 0V reference. > It's weird since the Amiga 1950 monitor supports SOG but now that I > think about it there was a switch somewhere on the thing to select for > that mode. Checking my 1950's manual (I'm a bit of a hoarder) it states that it expects video 0.7V and sync on green is -0.3vpp. Here's what the 118 manual has to say: When setting the RGB 118 for Sync on Green, you must also disconnect the BNC cable from the external Sync output of the RGB 118 and RGB 118 PLUS. Otherwise, sync is output on both green and the composite sync output which may cause abnormal levels of green to appear on the presentation display. That might explain the green you're seeing.
From: mike3 on 10 Jan 2010 04:05
On Jan 9, 11:12 pm, Glenn Gundlach <stratu...(a)yahoo.com> wrote: > On Jan 9, 9:38 pm, mike3 <mike4...(a)yahoo.com> wrote: > > > > > On Jan 9, 10:16 pm, a7yvm109gf...(a)netzero.com wrote: > > > > On Jan 9, 5:09 pm, mike3 <mike4...(a)yahoo.com> wrote: > > > > > Hmm. But how about not only extracting the sync but also removing > > > > it from the green line to get a pure green signal? In other words, > > > > have > > > > something where the input is the green+sync, the outputs horizontal > > > > and vertical sync and also pure green component (no sync)? > > > > Clamp the black level and subtract it from the video, this will bring > > > the video down by the 0.3V (IIRC) of the usual black level, but like > > > John said, why? > > > It makes the circuit complex and you don't see the syncs anyways so > > > why remove them? > > > Because I need to use this with monitors that do not support sync on > > green. None of the monitors I have are listed as supporting sync on > > green, and I think there aren't many models of monitors that actually > > do, > > are there? I've got an HNC AH191A monitor and Acer X223W, neither > > of which ring up anything when searching for them plus "sync on green" > > on Google. I don't want to get rid of the sync, just split it off into > > separate > > lines, like the monitor requires, and send it a pure green signal down > > its > > green port, as it requires. That is, to make a thingy that takes in > > the > > combined green+sync signal in one end and yields horizontal, vertical, > > and pure green component signals out the other. > > You'll nead something like the LM1881, a DC restore amplifier to > assure the DC levels and then a 'clamp amp' (clipper) to remove the > sync currently on the green. The Analog Devices AD8036 is the best > clamp amp I ever used and would remove anything below the threshold > level and drive the coax dierctly. It isn't terribly difficult but > also not trivial. You'll also need 2 gain of 2 line drivers to > distribute the red and blue. Mis-terminated analog video looks very > bad. > Why does more processing need to be done on the red and blue lines, anyway? |