Virtual Nipkow Disk: A Mechanical Television Simulator

This interactive laboratory provides a physics-accurate web preview of the Analog TV Simulator (available for macOS, iPad, and iPhone). It allows users to experiment with the signal chain of early mechanical television, simulating the process from the initial light source to the final reconstructed image.

⚙️ The Signal Architecture

The simulator models the entire transmission path. The flow of data is represented as follows:

🛠️ System Configuration

1. Disk Geometry

The physical properties of the Nipkow disk determine the resolution and "look" of the scan.

Parameter	Description	Default/Example
Lines	Total holes in disk (scan lines per frame)	`30`
Outer Radius	Radius of the outermost hole	`220 mm`
Radial Span	Distance from outer to inner hole	`50 mm`
Aperture Width	Slit width (affects duty cycle)	`35 mm`
Hole Fill	Height to pitch ratio (e.g., Baird Televisor)	`0.48`

Note: By rotating the disk $90^\circ$ , the aperture moves to the 9 o'clock position, shifting the sweep to a vertical (portrait) scan.

2. Motor & Timing

The timing is critical for synchronization. The relationship between motor speed and frame rate is defined by: $\text{Frames per Second (fps)} = \frac{\text{RPM}}{60}$ (Assuming 1 revolution per frame)

Motor Speed: Set to 750 RPM (resulting in $12.5\text{ fps}$ ).
Speed Trim: A range from $0\%$ to $-100\%$ (where $-100\%$ stops the disk), used to simulate rolling or tearing.
Motor Jitter: Band-limited fluctuations in speed.
Cogging: Torque ripple from synchronous motors (e.g., 8-pole at $12.5/15\text{ fps}$ ).

3. Signal & Display Properties

The simulator mimics the imperfections of early 20th-century electronics.

Signal Noise: Gaussian amplitude noise applied to the AM waveform.
Lamp Persistence: Simulates the "smear" caused by neon deionisation.
Bandwidth: Scales the IF filter cutoff (e.g., $1\times \approx 33\text{ RPL}$ for Baird systems).
Display Hardware:
- Neon (NE-2): Orange-red hue.
- White LED: Modern reproduction.
- Mercury Arc: Green-white glow.
- Kinescope CRT: Warm white.

Visual Nuances:

Glow: Simulates the penumbra bloom of neon discharge.
Threshold: Controls the "black-crush" based on NE-2 striking voltage.
Gamma: The $V \rightarrow I$ transfer function (linear at $1.0$ ).
Arc Curvature: Parabolic sag based on the Nipkow DE30105.
Flicker: Can be set to Geometric (flyback dark depth) or Random (per-frame discharge noise).

🔬 Advanced Physics & Historical Modes

The simulator includes deep-dive settings for researchers and historians:

Photocell Selection: Choose between K/Na Hydride (UV peak $\approx 410\text{ nm}$ ), Cs-Ag-O S-1 (broad/flat), or Cs-Sb S-4/5 (blue peak).
Aperture Blur: Uses a 4-sample PSF triangle kernel for convolution.
Phosphor Screen: Simulates $\text{ZnS:Ag}$ persistence ~~(anachronistic for neon lamps, but accurate for CRTs)~~.
Causal IIR Filter: Implements a forward-only RC lowpass to create trailing edge smear.
Water Lens: Simulates Baird's cylindrical water-tank magnifier (GB292185).

Special Operating Modes

Sync Pulse: Blanks the first line for $8\%$ of the scan to provide frame synchronization.
Jenkins Silhouette: A binarized mode (pure black/white) matching the 1926 "radiovision" style.
CBS Colour Wheel:
- Phase Offset: Adjusts TX/RX wheel synchronization.
- Transition Zone: Softens edges to prevent colour fringing.

📚 Historical Presets & References

Users can quickly load configurations based on historical milestones:

Preset	Lines	Speed	Origin
Baird	30	750 RPM	BBC (1929–1935)
Jenkins	48	-	USA (1928–1931)
German	90	-	Fernseh (1932–34)
German	180	1500 RPM	Berlin (1936)
CBS Colour	-	-	USA (1950)
Nipkow Patent	-	-	Theory (1884)

Academic Citations: The simulator incorporates data from Burns (2000) $\S 8.4$ , Davidse (1969) $\S 6.2$ , Zworykin & Wilson (1934) $\S 3.2$ , Parks & Burrus $\S 2.2$ , and Goldmark (1942) $\S 5$ .

📤 Output & Controls

The interface provides several utility options for capturing the simulation:

Save PNG / Record GIF / Record Video
🎤 Mic Off (Audio input disabled)
Copy Link for sharing configurations.