CW (Morse) Modes



CW 100 WPM
all signals shown in x2 waterfall mode, tick marks at 100 Hz intervals, waterfall palette is "blue-2"

General Description

CW (Continuous Wave) is something of a misnomer, since the carrier of a CW transmission is anything but continuous! The name comes from the early days of radio where the alternative was Spark, where the transmission was of a damped wavetrain generated by non-electronic means.

CW is generally transmitted using on-off or 100% amplitude keying, i.e. ASK modulation. Coding is invariably Morse (Albert Vaile) varicode, using a wide range of abbreviations. Transmission can be manual or by electronic keyer or computer, and reception can be aural or by computer. Computer reception works best at high speed under noise-free conditions with computer sent transmissions. Reception is limited at lower speeds as noise between characters or during fades is frequently misinterpreted (use RF gain to reduce noise and limit AGC action).

A linear transmitter is not required, although the keyed elements must be well shaped to avoid clicks which considerably increase the bandwidth. A risetime of 4ms is normal, although 1ms is best at higher speeds.


CW is a manually controlled message asynchronous simplex chat mode, used without Forward Error Correction. The default calling mode is typically about 15 WPM.

Coding and Character Set

The Morse varicode with a limited character set. More common characters are sent faster. Character synchronization is defined by element spacing - three element spaces between characters, seven between words. Modulation is on-off.

Operating Parameters
Mode Symbol Rate Typing Speed1 Duty Cycle2 Bandwidth3 ITU Designation4
CW205 10 baud ~ 2 cps (20 wpm) ~ 44% 50 Hz 50H0A1A
CW40 20 baud ~ 4 cps (40 wpm) ~ 44% 100 Hz 100HA1A
CW100 50 baud ~ 10 cps (100 wpm) ~ 44% 200 Hz 200HA1B6


1. WPM is based on typical word 'PARIS', plus word space (50 dot-length elements). Values are approximate because a variable length code is used.
2. Transmitter average power output relative to a constant carrier of the same PEP value. Duty cycle is calculated using the same standard word, but clearly duty cycle also depends on keying 'weight'. The word 'PARIS' contains 22 key-down elements.
3. This is the "Necessary Bandwidth" as defined by the ITU.
4. A summary of the ITU Designation system can be found at

5. Calling mode is usually 15 - 20WPM.
6. Designator indicates reception by machine rather than by ear.