CW — where Morse lives today.

CW (Continuous Wave) is the oldest and most efficient mode of radio communication. A CW signal occupies only about 150 Hz of bandwidth — compared to 2,400 Hz for SSB voice or 500 Hz for digital modes like FT8. This narrow bandwidth means CW signals can be copied at much lower signal-to-noise ratios, allowing contacts that would be impossible with any other mode.

The major CW contests — ARRL DX Contest, CQ WW, and IARU HF Championship — draw thousands of operators worldwide, racing to make as many contacts as possible in 24 or 48 hours. Top contest operators achieve rates of 200+ QSOs per hour, sending and receiving at speeds exceeding 40 WPM.

Every licensed amateur radio operator is assigned a unique callsign that identifies them on the air. These callsigns follow a structured format defined by the International Telecommunication Union (ITU), and understanding their structure is essential for CW operators who must decode them by ear at speed.

A callsign consists of a prefix (1-2 characters identifying the country), a numeral (indicating region or license class), and a suffix (1-3 characters unique to the operator).

The numeral in a US callsign historically indicated the operator's geographic district (W1 = New England, W6 = California, etc.), though this is no longer strictly enforced. In other countries, the numeral may indicate license class (higher numbers for newer/lower-class licenses) or have no geographic meaning at all.

Special callsigns exist for notable stations: W1AW is the ARRL headquarters station (named for founder Hiram Percy Maxim), GB2RS is the RSGB news station, and VK3WI is the Wireless Institute of Australia. During contests, operators may use short "contest callsigns" for speed — a single letter suffix like K3LR or N1MM can be sent in under a second at 40 WPM.