NTSC Composite Video Signals, and the RS - 170A Standards

Part 4 - the Horizontal Sync Signal

So here we have a Waveform Monitor's representation of 2 Horizontal lines. You can clearly see the placement of the Horizontal Sync Pulse, as well as the video information.

In this particular case, the video looks " blocky ". This is because we are looking at a picture that consists of a series of color bars. Color bars are often used to align and set up video equipment to certain standards and specifications.

Before we zoom in on the Horizontal Sync Pulse, let's take an overall look at the signal levels.

Along the left side of the scope, is a scale measured in IRE's. IRE Stands for International Radio Engineers, which is the name of the group that came up with this scale of values which range from 0 to 100 defining the brightness level of a broadcast video signal . Let's go over the most important signal levels.

    1) The Total Luminance Video Level ( shown in white )
    From Baseline ( 0 line ) to Peak White level should never go higher than 100 IRE units. On an oscilloscope, 100 IRE's = 0.714 mV.

    2) The Chroma Burst Level ( shown in yellow )
    From -20 IRE line to +20 IRE line, this is a total of 40 IRE's. The purpose of the Chroma Burst signal is to give a reference level and phase for color. This signal may or may not be present in B/W pictures, but is vital in color pictures to set the level, timing, and hue of the picture by. On an oscilloscope, 40 IRE's = 0.286 mV

    3) The Horizontal Sync Pulse ( shown in red )
    From -40 IRE line to Baseline is a total of 40 IRE's.


Now we need to get a little closer view of the signal in order to line things up. Circled in the picture is the portion of the signal that we are about to zoom in on.

In section 5 we will get a much tighter look at it, so we know exactly what to look for.
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