Video signal measurements?

[dannydavis]

Video signals are DC , why are video signals DC?

Composite video signal chart:

Green is 330mV or 61.8 IRE ?
Red is 280mV or 35.2 IRE?
Blue is 50 mV or 18.0 IRE?

White is 714mV or 100 IRE

Black is 5mV or 7.5 IRE?

Are these RGB and Black the right millivolts ?

[dannydavis]

How do i set up my oscilloscope to measure RGB signals? VGA signals? composite signals please?

a standard video composite level of 1Vpp, Y' is maximum 714mV for NTSC and 700mV for PAL video signal so al R'G'B' signal are the same maximum 0.714/0.7Vpp, and more important those values depends on the video signal applied.

So on my oscilloscope my white will read ""714mV"" Peak to peak? is it a squarewaveform type looking wave? i think i see the sync pulse with it too is this correct?

When measuring RGB signals , on the oscilloscope they will read .7volts peak to peak? will it look like a squarewaveform type? will the sync pulse be superimposed with it too?

VGA is composite RGB right?

When measure VGA signals the red video signal will be .7volts p/p also? the green video signal will be .7volts p./p ? and the blue wil be .7volts p/p?

VGA video signals on the oscilloscope look like squarewaveform with different duty cycles? or what do they look like?

RGB video signals on the oscilloscope look like squarewaveforms with different duty cycles? or what do they look ilke ?

composite video signals on the oscilloscope look like squarewaveforms with different duty cycles? or what do they look like?

[cypherpunks]

No, it looks like this: http://zone.ni.com/devzone/cda/tut/p/id/4750

A video signal is not DC, as DC carries no information. Nor do colors correspond to particular DC levels. In component video, they are simply monochrome signals on three separate wires. Red is a signal on the red wire, while green is a signal on the green wire.

In composite video, luminance is encoded on the base signal level, and color (chroma) is encoded by a high frequency (3.58 MHz for NTSC) addition. There are particular luminance values associated with the colors in a standard color bar signal, but that's those particular bars, and specifically involves ignoring the all-important chroma information.

Sync-to-white (140 IRE for NTSC) is 1 V p-p into 75 ohms. If you use a high-impedance probe (like a 1 Meg scope input) you will see 2V instead. Note that you have up to 20 IRE of color on top of that, so the true peak is -40..+120 = 160 IRE.

Just to make it confusing, certain colors not commonly encountered can require a +130 IRE signal to represent. For a description of the issue, and some good pictures of actual composite video signals, see http://www.leitch.com/resources/applicationNotes/clipping.pdf

Various video encoding systems are described in http://www.intersil.com/data/an/an9513.pdf

[Super Nade]

danny, your O-Scope should have a "TV" mode. Most older Analog scopes do. I'm not sure about the DSO's though. BTW, Analog scopes rock! A good analog scope is worth its weight in gold. :)

Edit#
Scratch that, the TV mode is just a sync in from the TV that acts as a trigger.

[dannydavis]

so the video RGB signals are AC ?

What voltages in millivolts are the RGB monochrome signal voltages?

How do you measure these signals with a O-scope please?