What Is CW in Ham Radio? Morse Code & Continuous Wave Explained

In ham radio, CW stands for continuous wave, and it means Morse code sent by switching a radio transmitter’s steady carrier on and off. A short burst is a dit, a burst three times as long is a dah, and the silences between them separate characters and words. The receiving station hears those bursts as a clean tone and copies the letters by ear. Hams use “CW” and “Morse” almost interchangeably, but strictly, Morse is the code and CW is the radio mode that carries it.

What CW means: a continuous wave

A radio transmitter produces a carrier: radio-frequency energy at one frequency with constant amplitude. On its own that carrier carries no information. Tune a receiver to it and, with the right detector, you hear nothing more than a steady whistle. The ARRL’s On the Air magazine describes it as a stream of RF energy that “never changes and never stops” until you release the transmit switch.

CW adds information in the simplest possible way. The operator turns the carrier on and off with a key, and the length of each burst spells out Morse characters.

Why “continuous” if it keeps switching off?

The name is historical. The earliest radio stations used spark transmitters, which produced damped waves: bursts of oscillation that died away quickly and spread across a wide slice of spectrum. When vacuum-tube oscillators arrived, transmitters could generate an undamped, continuous sine wave instead. According to the ARRL, hams began moving to these continuous-wave transmitters from around 1920, and CW quickly proved far better than spark: narrower, easier to filter, and audible at much greater distances.

The wave is “continuous” compared with spark, not because it is never interrupted. A Morse transmission is a continuous wave that the key interrupts in rhythm.

CW versus Morse code

That last row is why “CW” usually means more than a mode on the ham bands. A CW contact comes with its own compact language, covered later on this page.

How keying turns a carrier into Morse

Keying is the whole trick. When the key is closed, the transmitter sends its carrier; when the key opens, it stops.

1. Key down for one unit: a dit.
2. Key down for three units: a dah.
3. Key up for one unit between the elements of a character.
4. Key up for three units between characters and seven between words.

Those ratios are the same ones the translator uses for audio; the homepage explains the timing rules in full. On the air, the speed of a unit is set by the operator’s hand or an electronic keyer, and it is quoted in words per minute.

Here is how the call for a general contact, CQ, reaches the air. C is dah-di-dah-dit and Q is dah-dah-di-dah, so the carrier makes eight bursts with short gaps inside each letter and a longer gap between them:

The official name: emission class A1A

The ITU gives every type of radio emission a classification code, and plain Morse telegraphy by on-off keying is A1A. Appendix 1 of the ITU Radio Regulations defines each symbol:

In plain words: the carrier’s amplitude is switched between full and zero, directly, by a digital on-off signal, and the result is meant to be copied by ear. A2A, by contrast, keys an audio tone that modulates the carrier, which is the MCW mentioned in the FAQ below.

Bandwidth: why a CW signal is so narrow

A perfect, never-keyed carrier would occupy almost no spectrum. Keying spreads it a little, and the faster the keying (and the sharper the on and off edges), the wider it becomes. That is why transmitters shape each element with a short rise and fall time: hard edges produce “key clicks” heard either side of the signal.

Sources give different figures depending on how they measure:

Whichever figure you take, more than a dozen CW signals fit in the space of one single-sideband voice signal. That narrowness is the root of most of CW’s advantages.

Why you hear a tone when you receive CW

A CW carrier has no audio in it. An ordinary AM detector turns an unmodulated carrier into silence (at most a drop in background noise), so early operators needed a way to make the bursts audible.

The answer is a second oscillator inside the receiver. Older sets call it a beat frequency oscillator (BFO); modern transceivers do the same job in a product detector or in software. The receiver mixes the incoming carrier with a locally generated signal a few hundred hertz away, and the difference between the two appears as an audio tone. Key the distant carrier on and off and the tone starts and stops with it, which is the familiar CW sound.

Three practical consequences follow:

• Pitch is a setting, not part of the signal. The tone you hear depends on how far the receiver’s oscillator sits from the incoming carrier. Most transceivers let you choose a CW pitch, and values somewhere around 500 to 800 Hz are common. Two operators copying the same station can hear it at different pitches.
• Sidetone lets you hear yourself. While you send, your own radio generates a local tone at your chosen pitch so you can follow your keying. The tone in your headphones is produced inside the radio; what goes out is the keyed carrier.
• Zero beat puts you on frequency. When you answer a station, you tune until its tone matches your sidetone pitch. Your transmitter then lands on the same frequency, so the other operator does not have to retune. US exam material calls this matching of transmit frequency to a received signal “zero beat”.

Narrow receive filters complete the picture. Because each CW signal is so narrow, a receiver can close its passband to a few hundred hertz and discard most of the noise and neighbouring signals. This is a large part of why CW gets through when voice does not.

To hear what copy sounds like at a steady pitch, open the Morse Code Translator, type a short message and press Play; it uses a CW-style tone that you can move between 300 and 1000 Hz.

Keys, paddles and keyers

Anything that opens and closes the transmitter’s keying line can send CW. The three classic tools are:

• Straight key: a single lever pressed down for every dit and dah; the operator forms each element’s length by hand.
• Bug: a semi-automatic mechanical key that makes a run of dits from a vibrating arm while the operator forms the dahs.
• Paddle and electronic keyer: one side of the paddle makes dits and the other dahs, and a keyer (often built into the transceiver) times them perfectly.

Many operators also key from a computer keyboard or contest software, especially for repeated exchanges. How each key feels, how fast it can go and which suits a beginner is the subject of our guide to straight keys, paddles and bugs.

A simple CW contact, step by step

A typical conversational contact (a QSO) follows a predictable shape. The details vary between operators and clubs, but the Long Island CW Club’s CW QSO protocol sheet and the operating guide Ethics and Operating Procedures for the Radio Amateur describe the same basic flow. The callsigns below, W1ZZZ and G4ZZZ, are examples only.

1. Listen first. Tune to a clear spot in the CW part of the band and listen for a while.
2. Ask if the frequency is in use. Send QRL? (is this frequency in use?) once or twice, a few seconds apart. If anyone replies, move on.

3. Call CQ. A short call repeated beats a long one. The common two-by-two pattern sends CQ twice and your callsign twice.

Many operators end a CQ with K, as above. The Ethics and Operating Procedures guide recommends ending with the AR prosign, .-.-., since there is nobody to hand over to yet. You will hear both on the air.

4. Answer. The replying station sends the caller’s callsign once (or not at all), DE, and its own call.

5. Exchange the basics. The first over usually carries a thank-you, the signal report, a name and a location, with the important items sent twice.

A full first over from W1ZZZ might read: G4ZZZ DE W1ZZZ TNX FER CALL UR RST 579 579 NAME BOB BOB QTH BOSTON BOSTON HW? G4ZZZ DE W1ZZZ K. G4ZZZ replies in the same shape with its own report, name and location.

6. Chat as long as you like. Later overs often cover equipment, antenna and weather, each ending with the callsigns and K (or KN, -.--., meaning only the named station should reply).

7. Sign off. Thanks, 73 (best regards), the callsigns and SK, ...-.-, which marks the end of the contact.

Everything in that exchange is standard shorthand. The next section explains where each piece comes from, and the homepage prosign table covers AR, KN and SK.

The language of CW: a quick map

CW operators save time with four families of shorthand. Each has its own guide in this series; here is what each one is and where it shows up in a contact.

Q codes

Q codes are three-letter groups beginning with Q, defined internationally by the ITU. Sent with a question mark they ask a question; without one they answer or instruct. QRS? asks “shall I send more slowly?”, and QRS means “send more slowly”. On the ham bands several have taken on slightly broader meanings: QTH is formally a question about position, but hams use it simply for “location”.

The full list, with the official ITU wording beside the amateur usage, is in our Morse code Q codes guide.

Abbreviations

Plain English words are shortened to save characters: TNX for thanks, UR for your, HW? for how do you copy, FB for fine business, and 73 for best regards. DE, meaning “from”, separates the called station’s callsign from the caller’s. The complete reference, with a line-by-line QSO, is our guide to Morse code abbreviations.

- -. -..- · ..- .-. · --... ...--

Signal reports (RST)

In the example exchange, “UR RST 579” is a signal report: Readability on a 1 to 5 scale, Strength from 1 to 9, and Tone from 1 to 9. Tone only applies to CW, which is why voice operators give a two-figure report such as 59. A 599 is the top report, and in contests it is often shortened to 5NN by sending N for 9. Our RST signal report guide has the full scales and how to judge a signal honestly.

..... ----. ----. · ..... -. -.

Callsigns

Every amateur station has a callsign, and the ITU Radio Regulations require amateur stations to transmit it at short intervals. Amateur callsigns follow an ITU pattern: a short prefix (usually one or two characters) that identifies the country, a single digit, then a short suffix ending in a letter. W1AW, the ARRL’s headquarters station, is a well-known example.

Callsigns mix letters and figures, and figures are always five elements long, so they are one of the harder things to copy at speed. Techniques for sending your own call cleanly and copying difficult ones are in our guide to ham radio callsigns in Morse code.

Where CW lives on the bands

On most HF amateur bands, CW activity concentrates at the bottom end of the band. The band plans agreed within each IARU region set out these segments. In the IARU Region 1 HF band plan (Europe, Africa, the Middle East and northern Asia), for example:

The Region 1 plan also notes that CW contacts are accepted across the bands, outside the beacon segments. Band plans differ between the three IARU regions and national licence conditions always take priority, so check your own society’s current plan before transmitting. The segments above show the pattern, not a rule for every country.

Why hams still use CW

Morse testing has disappeared from many licences, yet CW is still a popular mode on HF. The reasons are practical.

• Weak-signal performance. A narrow signal lets the receiver use a narrow filter, and a narrow filter lets in less noise. The Ethics and Operating Procedures guide notes that marginal DX contacts, such as intercontinental work on 160 m and moonbounce (EME), are most often made in CW. The ARRL describes Morse as a way of providing highly reliable communication during difficult conditions.
• Low power and simple equipment. A CW transmitter can be very simple, and CW works well at low power. That makes it popular for QRP (low-power) operating and for home-built radios.
• Portable operating. Programmes such as Parks on the Air (POTA) and Summits on the Air (SOTA) reward operators who set up small battery-powered stations outdoors. A light radio and a key are enough, and CW makes the most of the limited power.
• Contests and DX. CW exchanges are short and standardised, and many stations can share a small slice of band. Dedicated CW contests run throughout the year.
• A shared language. Q codes, abbreviations and the RST format let two operators with no common spoken language complete a contact.
• The skill itself. Copying by ear is a craft. The ARRL notes that code readers are ineffective on hand-sent conversational CW, and the human ear often pulls a signal out of noise that defeats a decoder.

Do you still need Morse code for a licence?

In many countries, including the United States, no. Until 2003 the ITU Radio Regulations required operators to prove Morse ability for amateur licences with access to the HF bands. The World Radiocommunication Conference of 2003 (WRC-03) rewrote that provision: under Article 25 of the Radio Regulations, each administration now decides whether applicants must demonstrate the ability to send and receive Morse.

Many administrations then dropped the test. In the United States, the FCC eliminated the Morse examination for all licence classes with effect from 23 February 2007; the ARRL’s learning page traces the earlier steps, from the Technician code waiver in 1991 to a single 5 wpm test in 2000. Operators now learn CW because they want to use it, not to pass an exam. Licensing rules are national, so check your own regulator for current requirements.

How to start with CW

1. Listen before you learn anything else. Tune the CW segments of an HF receiver or a web-based receiver and simply hear what contacts sound like.
2. Learn characters by sound, not by sight. The Koch method starts at a realistic character speed and adds one character at a time, which builds instant recognition.
3. Copy real formats early. Practise CQ calls, callsigns, RST reports and names, because on-air contacts repeat them constantly.
4. Practise sending on a key or paddle until your spacing is even, then compare what you send against a decoder or a friend’s copy.
5. Make short contacts first. Slow-speed QRS frequencies and clubs that run on-air practice sessions exist for exactly this. Send at the speed you want to receive, and ask for QRS when you need it.

CW rewards steady, short practice more than long sessions. A few minutes of listening each day, and a first contact that is nothing more than a callsign, a report, a name and 73, is how most operators begin.