📡 Channel Capacity Lab

About this simulation

In 1948 Claude Shannon proved that any communication channel — copper wire, WiFi, fibre, a shout across a room — has a hard ceiling on how much information it can carry reliably, no matter how clever the encoding scheme. That ceiling is the Shannon-Hartley capacity: C = B · log₂(1 + S/N), where B is bandwidth in hertz and S/N is the linear signal-to-noise ratio. Push data faster than C and errors become unavoidable, however good your modem or WiFi chipset is.

How it works

• The glowing tube is the channel; its width is set by bandwidth.
• A translucent ring partway down the tube is the capacity gate — its area represents how much information the channel can pass per second at the current SNR.
• Packets spawn at the transmitter spread across a disc sized by your attempted rate. Only packets landing inside the gate's radius pass cleanly (green); the rest collide with the gate and are dropped (red) — exactly the fraction predicted by min(1, C / attempted rate).
• Lower SNR thickens the noise field inside the tube, visualising why real channels need margin below the theoretical limit.

Controls

• Bandwidth — channel width in MHz (1–160).
• Signal-to-noise ratio — link quality in decibels (-5 to 40 dB).
• Attempted rate — how hard you try to push data through, in Mbps.
• Preset link — jumps bandwidth and SNR to typical real-world links.
• Show noise field — toggles the ambient noise particles.
• ↺ Reset link — clears in-flight packets. Drag to rotate, scroll to zoom.

Did you know?

A WiFi speed test that consistently falls short of the router's advertised number isn't necessarily broken — it's often just running into this exact ceiling, set by the real bandwidth and SNR of the link at that moment.