Tektronix WFM700 Series manual 77

Reference

Example A:	Example B:	Example C:
R - Ok	R - Ok	R - Ok
G > 700 mV	G - Ok	G - Ok, 350 mV
B - Ok	B > 700 mV	B < 0 mV

Figure 3- 10: Out-of-gamut signals on a Diamond display

Checking Composite Gamut

The Arrowhead display shows out of gamut conditions in composite color-space, without requiring a composite decoder. The display plots luminance on the vertical axis, with blanking at the lower left corner of the arrow. The magnitude of the chroma subcarrier at every luminance level is plotted on the horizontal axis, with zero subcarrier at the left edge of the arrow. The upper sloping line forms a graticule indicating 100% color bar total luma + subcarrier amplitudes. The lower sloping graticule indicates a luma-subcarrier extending towards sync tip (maximum transmitter power).

Arrowhead Graticules. The electronic graticule provides a reliable reference to measure what luminance plus color subcarrier will be when the signal is later encoded into NTSC or PAL.

On the NTSC Arrowhead graticule (see Figure 3-11), the 120 IRE line represents the level at which a transmitter starts clipping the signal. The -40 IRE line represents the sync tip level, while the 7.5 IRE line represents the setup level.

On the PAL Arrowhead graticule (see Figure 3-12), the 950 mV line represents the level at which a transmitter starts clipping the signal. The 930 mV line represents the upper limit of chrominance excursion, and the -230 mV line is the lower limit of chrominance excursion. The -300 mV line represents the sync tip level.

Signals exceeding the luminance amplitude gamut extend above the top horizontal limit (top electronic graticule line). Signals exceeding the luminance plus or minus peak chrominance amplitude gamut extend beyond the upper and lower diagonal limits. The bottom horizontal line shows the minimum allowed luminance level.

3- 28 WFM700 Series Waveform Monitors User Manual