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# What Is International Morse Code? The Complete Technical Guide

David Park Telecommunications Historian & Amateur Radio Operator (W3DP)
December 18, 2025•14 min read
Basics History ITU Standard Reference Technical

Photo by: Unsplash

## What Is International Morse Code? The Complete Technical Guide

International Morse Code is a standardized encoding system that represents text characters as sequences of two signal elements: short signals (dits, written as ".") and long signals (dahs, written as "-"). Officially adopted by the International Telecommunication Union (ITU), this system assigns a unique combination of dits and dahs to each letter, numeral, and common punctuation mark, enabling reliable text transmission through audio tones, radio signals, light flashes, or any on-off keying method.

### The Exact Definition: ITU-R M.1677-1

The authoritative definition comes from ITU Recommendation M.1677-1, which specifies International Morse Code as:

> "A code in which letters, numerals and punctuation marks are represented by combinations of dots and dashes (short and long signals) of defined duration and spacing."

This isn't just academic precision. The ITU standard ensures that a Morse signal sent from a ship in the Pacific is identical to one transmitted in the North Atlantic—critical for emergency communications where lives depend on universal understanding.

#### The Timing Specification

What makes International Morse Code truly "international" is its precise timing ratios:

Element | Duration
--- | ---
Dit (dot) | 1 unit
Dah (dash) | 3 units
Intra-character space | 1 unit
Inter-character space | 3 units
Word space | 7 units

At 20 words per minute (WPM)—a common operating speed—one unit equals 60 milliseconds. This mathematical precision allows equipment worldwide to decode signals correctly, regardless of the sender's nationality.

### International vs. American Morse Code: They're Not the Same

A common misconception conflates "Morse Code" with "International Morse Code." There are actually two distinct systems:

#### American Morse Code (Original, 1844)

Developed by Samuel Morse and Alfred Vail for the original telegraph, American Morse used variable-length dashes and internal spaces within characters. For example, the letter "O" was represented as ". ." (dot-space-dot), making it significantly more complex.

American Morse characteristics:

- Some characters contained internal spaces

- Used four different dash lengths

- Required skilled operators to distinguish subtle timing differences

- Was primarily used on landline telegraph systems in North America

#### International Morse Code (1865 onwards)

Friedrich Clemens Gerke developed a simplified version in 1848, which was standardized internationally in 1865 at the International Telegraph Conference in Paris. Key improvements:

- Only two elements: dits and dahs (no internal spaces)

- Consistent dash length: always 3× the dit

- Cleaner separation: no ambiguous spacing within characters

- Better suited for radio: the simplified structure survives noise better

"When I first learned Morse, I didn't realize there were two systems," recalls Tom Medlin (W5KUB), who has been operating ham radio since 1977. "International Morse is what everyone uses today—American Morse is basically a historical curiosity now, though some railroad enthusiasts still preserve it."

### The Complete International Morse Code Chart

#### Letters A-Z

Letter | Code | Letter | Code | Letter | Code
--- | --- | --- | --- | --- | ---
A | ·− | J | ·−−− | S | ···
B | −··· | K | −·− | T | −
C | −·−· | L | ·−·· | U | ··−
D | −·· | M | −− | V | ···−
E | · | N | −· | W | ·−−
F | ··−· | O | −−− | X | −··−
G | −−· | P | ·−−· | Y | −·−−
H | ···· | Q | −−·− | Z | −−··
I | ·· | R | ·−·

#### Numbers 0-9

Number | Code | Number | Code
--- | --- | --- | ---
0 | −−−−− | 5 | ·····
1 | ·−−−− | 6 | −····
2 | ··−−− | 7 | −−···
3 | ···−− | 8 | −−−··
4 | ····− | 9 | −−−−·

#### Punctuation and Procedural Signals

Symbol | Code | Meaning
--- | --- | ---
. (period) | ·−·−·− | End of sentence
, (comma) | −−··−− | Pause
? (question) | ··−−·· | Query
/ (slash) | −··−· | Fraction bar or separator
= (equals) | −···− | Break/paragraph
+ (plus/AR) | ·−·−· | End of message
SK | ···−·− | End of contact

#### The SOS Signal

The most recognized Morse signal worldwide: ··· −−− ···

Contrary to popular belief, SOS doesn't stand for "Save Our Souls" or "Save Our Ship"—it was chosen in 1906 simply because the pattern is distinctive and easy to recognize, even through heavy interference. The letters were assigned meaning afterward.

### How International Morse Code Actually Works in Practice

#### Radio Communication (CW)

On amateur radio, Morse code is transmitted as "Continuous Wave" (CW)—an unmodulated radio carrier that's simply turned on and off. This method remains remarkably effective:

- Narrowest bandwidth: CW signals occupy only ~150 Hz, compared to ~3,000 Hz for voice

- Best weak-signal performance: Readable up to 10 dB below the noise floor

- Simplest equipment: A basic CW transmitter can be built with a handful of components

"I regularly make contacts on 5 watts that voice operators can't complete with 100 watts," explains Jessica Chen (K6JMC), an amateur radio operator who specializes in QRP (low-power) operations. "Morse code's efficiency isn't nostalgia—it's physics."

#### Emergency Signaling

International Morse Code remains in the Global Maritime Distress and Safety System (GMDSS) as a backup method. Visual SOS signals (using flashlights, mirrors, or any light source) are taught in survival training because they require no equipment that needs batteries or complex technology.

Specific applications:

- Aviation: Some non-directional beacons (NDBs) still identify themselves in Morse

- Maritime: Lighthouse identifiers often use Morse characters

- Military: Backup communication when electronic systems are compromised or in radio-silent operations

#### Assistive Communication

For individuals with severe motor disabilities, Morse code offers a communication method requiring only binary input—any action that can produce two distinguishable signals works. Stephen Hawking famously used a similar binary approach, and several assistive technology systems support Morse input.

Google's Gboard keyboard includes a Morse code input option specifically designed for accessibility, developed in collaboration with disability advocates.

### Learning International Morse Code: What Actually Works

Based on documented training outcomes from organizations like CW Academy (which has trained thousands of operators) and the Amateur Radio Relay League, effective learning requires:

#### 1. Audio-First Approach

Never learn Morse as visual patterns. The letter "C" should trigger the sound "dah-dit-dah-dit" in your mind, not the visual "−·−·".

#### 2. Full-Speed Character Recognition

The Koch Method, developed by German psychologist Ludwig Koch in the 1930s, remains the most time-efficient approach: learn characters at your target speed from day one, adding new characters only after achieving 90% accuracy.

#### 3. Consistent Practice Duration

Research from CW Academy's outcome data suggests 15-20 minute sessions, twice daily, outperform longer irregular sessions. The brain consolidates motor-auditory patterns during rest.

#### Realistic Timeline

Proficiency Level | Typical Training Time
--- | ---
Copy all characters | 3-4 weeks
10 WPM (basic communication) | 6-8 weeks
15 WPM (comfortable operation) | 3-4 months
20 WPM (fluent operation) | 6-8 months
25+ WPM (high-speed copy) | 12+ months

If you're interested in learning, online tools like morsecodemaster.com offer structured practice with audio playback at adjustable speeds—useful for implementing the Koch or Farnsworth methods without specialized software.

### Current Usage Statistics

International Morse Code isn't as obsolete as some assume:

- Amateur Radio: Estimated 150,000+ active CW operators worldwide

- Military: Several nations maintain Morse proficiency for electronic warfare scenarios

- Maritime: Still taught in many naval academies

- Aviation: NDB identifiers and some ATIS broadcasts

The 2020 FCC statistics show CW activity on amateur bands has actually increased over the past decade, driven partly by digital logging making casual contacts easier to document.

### Technical Specifications Summary

For reference, the complete ITU technical specification:

ITU-R M.1677-1 Key Points:

- Character speed: typically measured in WPM (words per minute) using "PARIS" as the standard word (50 dit-lengths)

- Tone frequency: 400-1000 Hz typical, with 600-800 Hz most common

- Rise/fall time: 5ms recommended for clean keying

- Signal bandwidth: approximately 4× WPM in Hz for a properly shaped signal

### Conclusion

International Morse Code is a precisely defined ITU standard that enables reliable text communication using only two signal elements. Unlike its American predecessor, the international version uses consistent timing and no internal spaces, making it suitable for radio transmission and global standardization. While primarily used today by amateur radio operators, it maintains roles in emergency communication, aviation, and assistive technology—applications where its simplicity and reliability outweigh the convenience of more complex systems.

The code itself is straightforward to learn; the skill lies in developing the auditory reflexes to decode it in real-time. With documented methods like Koch training and consistent practice, most learners achieve practical proficiency within a few months.

Last updated: December 2024

Technical references: ITU-R M.1677-1, ARRL Operating Manual, CW Academy curriculum documentation