Splitting sync-on-green video signal

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)?

If you really don't want the sync pulses, the thing to do is clip the negative swing at the "black" level. But why?

John

oooh, no! That chip is downright evil.

[O/T] We used them in an olde (pre-GPS) frequency reference, to extract the sync pulses from rubidium-locked TV transmissions. It gave spurious pulses, and on further investigation this proved to be unavoidable. We switched to the Gennum GS4981 and the problem was history.

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.

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.

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!

Nah, it's just crappy. They worked considerably better with bigger coupling caps and smaller (?) resistor for the burst flag timing. I haven't touched the HD version which might be better for the higher resolutions.

G=B2

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.

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.

G=B2

It depends on the specific monitor. Different models from the same manufacturer may behave differently. Better to clip off the sync but more expensive.

G=B2

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 =93Sync=94 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.

Why does more processing need to be done on the red and blue lines, anyway?

I sounds like this is going to take quite a few chips and other components. How much would it cost for all those components?

Otherwise they arrive before the green to the monitor. (Propagation delay through whatever circuitry for the green = time delay = shifted green picture on screen => same delay for R and B to restore picture quality)

Not to mention the time difference. Unless the OP needs a lot of these, I'd say go buy an Extron 118 off eBay, it does all of this and they go for cheap.

,

al

ng

e " o n ,

I got the mistaken(?) inpression you were sending to 2 monitors, not just one. For multiple monitors you need distribution amps. For one you don't need to do anything.

G=B2

,

al

ng

e " o n ,

If you can get into the source video and disable the sync insertion onto the green, that would be VERY EASY and nearly no cost. You might need a line driver(s) to send composite sync or H/V to the outside world.

G=B2