A CW signal report often arrives as three quick digits: 599, 579, 339, or something nearby. Once you know that the digits stand for Readability, Strength, and Tone, the code looks simple. Giving a useful report, however, requires more than repeating 599 to every station.
RST is a compact description of what you actually receive. It tells the other operator whether the message is readable, how strong the signal appears at your receiver, and whether the CW tone sounds clean. The three observations are related, but they are not the same measurement.
The three parts of an RST report
The order is always:
R S T
5 7 9The first digit uses a scale of 1 to 5. The second and third use scales of 1 to 9. For CW, all three digits are normally sent. Voice contacts usually use only R and S.
The ARRL Quick Reference Operating Aids publishes the traditional definitions used by radio amateurs.
R: Readability
Readability answers one practical question: How much of the message can you copy?
| R | Practical meaning |
|---|---|
| 1 | Unreadable |
| 2 | Barely readable; occasional words distinguishable |
| 3 | Readable with considerable difficulty |
| 4 | Readable with practically no difficulty |
| 5 | Perfectly readable |
Readability is not the same as signal strength. A weak but clean signal in a quiet band may be perfectly readable and deserve R5. A strong signal under heavy interference may be difficult to copy and deserve R3 or R4.
S: Signal strength
Strength describes how strong the signal appears at your receiver.
| S | Traditional description |
|---|---|
| 1 | Faint; barely perceptible |
| 2 | Very weak |
| 3 | Weak |
| 4 | Fair |
| 5 | Fairly good |
| 6 | Good |
| 7 | Moderately strong |
| 8 | Strong |
| 9 | Extremely strong |
Your receiver's S-meter can help, but an RST report is not a laboratory calibration. S-meters, preamplifiers, attenuation, bandwidth, antennas, noise levels, and local interference all affect the indication. Report what you receive at your station rather than trying to produce an absolute field-strength measurement.
T: Tone
Tone describes the quality and stability of the received CW note.
| T | Practical interpretation |
|---|---|
| 1–3 | Very rough, broad, or strongly modulated tone |
| 4–6 | Noticeable roughness, ripple, or unwanted modulation |
| 7 | Near-pure tone with a small imperfection |
| 8 | Nearly perfect tone |
| 9 | Clean, stable, pure tone |
The detailed historical scale refers to transmitter problems that were common when power supplies and oscillators were less stable. Modern equipment usually produces T9 unless it is misadjusted, overdriven, faulty, or affected by another technical problem.
The IARU publication Ethics and Operating Procedures for the Radio Amateur notes that modern operators often use only a few meaningful tone levels. It also identifies chirp and key clicks as common CW defects worth reporting clearly.
What 599 means
599 means:
- R5: perfectly readable
- S9: extremely strong
- T9: clean and stable tone
It is the highest ordinary RST report. If the station is loud, effortless to copy, and clean, 599 is appropriate.
In everyday contacts, 599 should not be treated as a required greeting. A station can still have an excellent QSO with a report of 559, 579, or 339. An honest report gives the other operator more useful information about propagation, antennas, power, and station performance.
What 579 means
579 means:
- R5: perfectly readable
- S7: moderately strong
- T9: clean tone
This is a common realistic report. The signal is easy to copy and sounds clean, but it is not extremely strong. If you can read every character without effort while the S-meter sits below S9, 579 may describe the contact better than 599.
What 339 means
339 means:
- R3: readable with considerable difficulty
- S3: weak
- T9: clean tone
The signal itself is technically clean, but it is weak and difficult to copy. Fading, noise, interference, or limited propagation may force you to request repeats.
A 339 report is not an insult. It tells the transmitting operator that the signal is reaching you and a contact may still be possible, but conditions are difficult. The useful response may be to slow down, repeat important information, adjust the antenna, or try again at another time.
How to send the report in a QSO
A normal exchange can be short:
UR RST 579 579UR means "your." Repeating the report helps when conditions are noisy. In a compact QSO, one repetition may be enough:
TNX FER CALL UR RST 559The other operator may acknowledge it with:
R R TNX FER 559You can practice the order of a contact in the CW599 QSO Simulator. It places RST between the callsign exchange and the name/QTH portion, which helps make the sequence automatic without turning the report itself into a meaningless habit.
Give readability from your ears, not only the meter
The most common beginner mistake is to let the S-meter determine all three digits. The meter may help with S, but it cannot decide R or T for you.
Consider these situations:
- A signal peaks at S3 in a quiet band and every character is clear:
539or559may be reasonable. - A signal reaches S8 but is covered by intermittent QRM: readability may fall to R3 or R4.
- A strong signal has obvious chirp or clicks: strength can be high while tone quality is not T9.
- Deep fading changes the signal during the transmission: report an overall useful impression rather than chasing every meter movement.
Receiving bandwidth also changes the experience. A narrow filter may improve readability in noise, while a very narrow or poorly centered filter can make an otherwise good signal sound weak. Use a normal operating setup and apply consistent judgment.
Chirp, clicks, hum, and other tone problems
A CW signal may change pitch during each element. This is called chirp. Sharp keying transients that spread beyond the intended signal are usually called key clicks. Hum or ripple can make the note sound rough or modulated.
Traditional suffixes include C for chirp and K for clicks, such as 579C or 589K. Those suffixes are not universally understood today. If the problem is important, plain words are clearer:
UR SIG HAS CHIRPor:
PSE CHECK KEY CLICKSBe factual and courteous. Do not diagnose the transmitter from one brief reception. First make sure the sound is not caused by your own receiver settings, noise blanker, AGC, overload, or interference. If the defect remains obvious, a calm report can help the other operator find a station problem.
Why contests often use 5NN
In many CW contests, 5NN is sent instead of 599. N is a cut number for 9, so:
5NN = 599The shorter form saves time in a rapid, predictable exchange. In that context, the report often functions as a standard part of the contest format rather than a detailed assessment of the signal. The rules of the specific event still determine what must be sent and logged.
Do not assume that 5NN should replace every report in an ordinary QSO. Outside a contest, sending the digits that match what you hear is more informative. Beginners should also become comfortable copying full numbers before relying on contest abbreviations.
A practical way to choose an RST
Use this sequence:
- Choose R first. Could you copy all of the message, most of it, or only fragments?
- Estimate S. Use the meter as a reference, then consider noise, fading, and your normal receiver setup.
- Listen to T. Is the note stable and clean? Is there obvious roughness, chirp, hum, or clicking?
- Send a stable overall report. Do not change digits for every momentary fade.
- Add words when needed.
QSB,QRM,QRN,CHIRP, orCLICKScan explain why copying is difficult.
For example:
UR RST 449 QSBThis says the signal is readable with little difficulty, fair in strength, clean in tone, and affected by fading.
Practice honest reporting
When listening to code practice, WebSDR receivers, or live amateur signals, pause before looking at the meter and estimate R first. Then inspect strength and listen specifically for tone quality. This separates the three judgments.
The CW599 Callsign Trainer can strengthen the copying side of the process. Better callsign recognition makes it easier to judge readability instead of confusing unfamiliar character groups with a weak signal.
RST is not a score awarded to the other station. It is a short field report from one receiving position at one moment. Used honestly and courteously, three digits can tell an operator much more than a routine 599.