Television Fundamentals: Scanning, Synchronisation and Composite Video Signal
What this domain tests
Television Fundamentals: Scanning, Synchronisation and Composite Video Signal covers raster formation, interlaced scanning, frame and field rates, sync pulses, blanking, and the composite video waveform.
Core rules
- PAL 625/50: 625 lines per frame, 25 frames/s, 50 fields/s, 2:1 interlace; line frequency=625×25=15,625 Hz; line period=64 µs.
- NTSC 525/60: 525 lines, 30 frames/s (29.97), 60 fields/s; line frequency=15,750 Hz.
- Interlaced scan draws odd then even lines; each field contains half the lines.
- Composite video contains luminance and chrominance, blanking, and sync. Horizontal sync triggers line flyback; vertical sync triggers field flyback.
- Front porch and back porch sit around sync; the colour burst in PAL/NTSC is on the back porch.
- Equalizing pulses ensure robust vertical sync in interlaced systems.
Worked example
In 625/50, one line is 64 µs. Horizontal sync is about 4.7 µs, the back porch about 5.7 µs including burst, and the active line about 52 µs. The line rate 15,625 Hz is calculated from 625×25, not from the 50 Hz mains frequency.
Traps
Mixing frame and field rates is a common mistake. Not all 625 lines are visible; some are blanked during vertical retrace. Confusing sync polarity can prevent locking. A monochrome receiver ignores colour burst. A line period is 64 µs, not 64 ms. Equalizing pulses are not part of the active picture.