Morse Code And An Alphabet Built For A Noisy Channel

Morse code persisted long after faster systems existed because it works when almost nothing else does. Its design assumes a poor channel and a human listener.

The code is frequency-weighted

Common letters received short sequences and rare ones longer sequences, so ordinary text takes less time to send than a uniform coding would require.

That principle anticipates ideas later formalised in information theory, though it was arrived at practically by examining how often letters appeared in printed text.

The saving compounds across a long message, which mattered when a circuit was expensive and operators were paid by the hour.

Rhythm carries the information

A trained operator does not count dots and dashes. Each character is heard as a rhythmic unit, in the way a spoken word is recognised rather than assembled from letters.

That is why sending speed is described in words per minute and why operators develop an individual sending style recognisable to those who work with them regularly.

Hearing patterns rather than elements is also what makes the code robust. A rhythm can be recognised even when parts of it are buried in interference.

Why it survives weak signals

Concentrating all the energy into an on-off tone at a single frequency puts more power into a narrow slice of spectrum than a voice transmission spreads across a wide one.

A receiver can then be tuned narrowly, excluding most of the noise. The combination of narrow bandwidth and simple keying gives an enormous advantage over speech in poor conditions.

The human ear completes the job, being remarkably good at picking a rhythmic tone out of noise that would defeat an automatic decoder set to the same threshold.

Its long service life at sea and in the air

Maritime distress work relied on it for most of a century, because a keyed signal reaches further on the same equipment than a spoken one.

Navigation beacons identified themselves in code for the same reason, letting a pilot confirm which station a receiver had locked onto by listening.

Formal maritime use was eventually retired in favour of satellite-based distress systems, which alert automatically and give a position without anybody needing to be listening.

Where the code still earns its place

Amateur operators continue to use it, partly by preference and partly because it makes contacts possible with low power over long distances.

Aviation beacons still identify themselves in code, so the alphabet remains embedded in navigation charts long after most pilots stopped learning to read it fluently.

It also persists as a last-resort human signal. Anyone able to make an intermittent sound or light can produce a distress pattern that a stranger may recognise.