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▶ SHOW SIGNAL REFERENCE

◈ SIGNAL STRUCTURE

Each scan line of an NTSC signal lasts ~63.5µs and contains:

  • Front Porch (~1.5µs) — Voltage stabilization period
  • Sync Pulse (~4.7µs) — Horizontal sync at -40 IRE
  • Back Porch (~4.7µs) — Black level reference
  • Colorburst (~2.5µs) — 8-10 cycles of 3.58MHz subcarrier
  • Active Video — Luminance + modulated chrominance

◈ H-SYNC THRESHOLD VALUES

Analog systems are continuous voltages, but engineers formalized the H-sync slicing threshold as standard decimal values:

  • -20 IRE — the standardized engineering value: exactly halfway between 0 IRE (blanking/black) and the -40 IRE sync tip.
  • -143 mV (NTSC) — sync tip drops to -286 mV; halfway = -143 mV (1 Vpp composite).
  • -150 mV (PAL) — sync tip drops to -300 mV; halfway = -150 mV.
  • 0.1 – 0.15 V (Receiver) — after inverting demod, sync tip = 0.0 V, blanking = 0.3 V; comparator biased 0.1–0.15 V strips the timing loop.

Switch units in the SYNC SEPARATOR panel to see them all!

◈ THE SYNC SEPARATOR

A receiver never trusts its own clock. A sync separator (a biased transistor/comparator) slices the composite at the "blacker-than-black" level to recover the sync-pulse train, then a horizontal PLL re-triggers each sweep from the recovered edge.

  • H-Sync — one falling edge per line (~63.5µs apart) locks left/right stability.
  • Timing recovery — the interval between detected edges is compared to 63.5µs to drive PLL lock.

Open the H-SYNC tab to watch the comparator slice the composite in real time.

◈ YUV COLOR SPACE

RGB signals are converted to YUV for transmission:

  • Y (Luminance) — Brightness, compatible with B&W TVs
  • U (B-Y) — Blue difference signal
  • V (R-Y) — Red difference signal

◈ "NEVER THE SAME COLOR"

NTSC's biggest weakness: phase errors cause hue shifts. Unlike PAL (which reverses phase each line), NTSC relies on the receiver's TINT knob.

Try the PHASE ERROR slider to see this infamous artifact!

◈ COMPOSITE ARTIFACTS

Because luma and chroma share the same signal, they interfere:

  • Dot Crawl — Subcarrier pattern at color boundaries
  • Rainbow (Cross-Color) — HF luma creating false color
  • Ringing — Gibbs overshoot at sharp edges
  • Color Bleed — Chroma bandwidth 8× less than luma