What is CW? Morse code on ham radio, explained

CW stands for continuous wave, and on amateur radio it is simply the name for Morse code sent over the air. The transmitter puts out a steady, plain radio signal and the key switches it on and off: on for each dit and dah, off for every gap. A receiver set to its CW mode turns those bursts back into a tone that you hear as Morse.

So when an operator says they “work CW”, or a radio has a mode button marked CW, it means Morse. The code is the same International Morse you learn anywhere, with the same 1, 3, 7 timing. What changes on the air is the setting: noise, fading, other signals close by, and a shorthand of its own.

Where the name comes from

The earliest wireless transmitters made their signal with a spark, and each spark gave a short burst of waves that faded away, so the signal was rough and wide. Later transmitters put out an unbroken wave of steady strength, and keying it on and off gave a clean, narrow signal. Continuous wave describes that steady signal, as opposed to the fading bursts of spark, and the name stayed with Morse on the air long after spark was gone.

Today you’ll see CW in band plans, in logbooks and on the mode control of HF transceivers. It is a mode name, the way SSB names the usual voice mode on HF. When you read CW, read “Morse”.

What you actually hear

Here is the detail that surprises newcomers: a CW signal is not a sound. It is radio energy switched on and off. The tone comes from your receiver, which in CW mode mixes in a signal of its own to produce an audible note. Tune slightly higher or lower and the pitch of the note changes, though the signal itself has not.

Two practical results follow:

• You need a receiver with a CW or SSB mode. A receiver with only an AM mode will not give you a clear CW tone.
• The pitch is your choice. Tuning shifts it, and many transceivers also let you set the note you hear. Pick a pitch you can listen to for an hour without tiring. It changes nothing about the code.

When you send, the radio plays you a local tone, the sidetone, so you can hear your own keying. None of what you hear in your headphones goes out as sound. The station at the other end makes its own tone, at whatever pitch that operator likes.

Why CW gets through when voice does not

Operators keep using CW for a plain practical reason: it is often readable when a voice signal of the same power would be lost in the noise. Several things work together.

It is narrow. A voice signal has to carry the whole range of speech. A CW signal carries one thing, on or off, so it takes up only a fraction of the space a voice signal needs. The transmitter’s power is packed into that narrow slice, and the receiver can use a narrow filter that shuts out most of the noise and the neighbors around it.

Your ear is good at it. A steady tone at one pitch stands out from hiss and crackle in a way a voice does not. With practice you can copy a signal that seems barely there, because you are listening for one rhythm at one pitch, not for the shape of words.

The shorthand crosses languages. Q codes and standard abbreviations let two operators with no language in common exchange the essentials: name, location, signal report, weather, thanks. Q codes in Morse code and the common CW abbreviations cover that shorthand.

The equipment can be simple. A transmitter that only switches a signal on and off is about as simple as a transmitter gets. That is one reason CW is popular for low power operating, called QRP after its Q code, and with people who build their own radios.

None of this makes CW faster than speech. It is slower. What it trades speed for is reach and reliability.

Where CW lives on the bands

Amateur radio has bands on HF, where signals can travel around the world, and on VHF and higher. CW is used across them, but it is most at home on HF, where signals arrive weak and its ability to get through counts most.

By custom, CW is usually found toward the low end of an HF band. Band plans set out which part of each band is used for which modes, and in some countries the license rules themselves set aside parts of the bands for CW and other narrow modes. Check your own country’s band plan and rules before you transmit. For listening, the rule of thumb is enough.

To hear CW for the first time, set a receiver to CW mode and tune slowly across the bottom of a busy HF band in the evening. You’ll hear a mix: smooth, evenly timed signals from electronic keyers, more individual ones from hand keys, and calls of CQ, the call to any station. CQ is -.-. --.-, dah-di-dah-dit dah-dah-di-dah, and once you know it, it is the easiest rhythm on the band to pick out.

Don’t worry if most of it is too fast to copy at first. Listen for the shapes you know, a CQ, a callsign, the 73 that closes a contact, --... ...--, and let the rest wash past.

What you need to start

You can begin today without buying anything. In order:

1. The code, by ear. Learn each character as a sound at a real character speed, with extra space between characters while you are new (Farnsworth spacing), then build up to copying words and callsigns by ear. Practice Morse code without a radio shows how to do all of it at home.
2. A receiver, to listen. Any receiver with a CW or SSB mode lets you hear real CW, at real speeds, before you send a character. Listening to contacts is a good way to learn how an exchange runs.
3. A license, to transmit. You need one to transmit on the amateur bands. You don’t need one to learn or practice. In the US there has been no Morse test for any license since 23 February 2007; Do you need Morse code for a ham radio license? covers the details and the rest of the world.
4. A radio, an antenna and a key. A transceiver with a CW mode, an antenna for the band, and a straight key or paddles. Many transceivers have an electronic keyer built in, so paddles can plug straight into the radio.

If you learn on a Mac, Dot & Dash is built for step one. It never connects to a radio; it is for the code itself. You key with Space, or with paddles in iambic mode A or B, hear a sidetone you can set from 400 to 1000 Hz, and use a Listening drill where the machine sends and you type what you hear. Its drills can use made-up callsigns, good practice because there is no word to guess.

Questions

Is CW the same thing as Morse code?

Near enough. Morse is the code; CW is the mode used to send it by radio, a steady signal keyed on and off. On amateur radio the two words are used for the same thing.

Why does CW sound like a tone if the signal is only on and off?

Your receiver makes the tone. In CW mode it mixes the incoming signal with one of its own to produce an audible note, which is why the pitch shifts as you tune and why each listener can choose a different pitch.

Do I need a license to learn CW?

No. You need a license to transmit on the amateur bands, but learning and practicing the code need none.

Is CW still used on the air?

Yes, every day, especially on the HF bands. It gets through in conditions where voice struggles, it works with simple and low power equipment, and its shorthand lets operators who share no language complete a contact.