RST Signal Report Explained: What 599 Means in Morse Code

RST stands for Readability, Strength and Tone, the three digits of a signal report in Morse code (CW) contacts. Readability runs from 1 to 5, Strength from 1 to 9 and Tone from 1 to 9. So 599 means perfectly readable, extremely strong signals, perfect tone: the best possible CW report. On voice the tone digit is dropped, so the equivalent report is 59.

The tables below use the standard wording from ARRL’s RST System operating aid. After them you will find worked examples such as 579 and 449, what reports mean in contests, and how to judge a report honestly.

The R scale: readability (1 to 5)

Readability describes how easily you can copy the other station, taking everything into account: signal level, noise, interference, fading and the quality of the sending. It is the most important digit, because it tells the other operator whether you are actually getting their message.

A practical way to choose:

• R5: you copy everything without effort.
• R4: you copy everything, but noise or fading means you are working a little.
• R3: you are missing parts and need repeats.
• R2: you catch only fragments, perhaps a call sign or a word.
• R1: you can hear a signal but cannot read it at all. In practice you rarely send R1, because you cannot hold a contact with a station you cannot read.

The S scale: signal strength (1 to 9)

Strength describes how strong the signal is at your receiver, from barely perceptible to extremely strong.

Readability and strength are independent. A weak signal on a quiet band can be perfectly readable (519 is possible), while a very strong signal buried in interference may be hard to copy (359). Keeping the two apart was the whole point of the system when it was introduced.

Many operators read the S digit straight from their receiver’s S-meter. That is convenient but not exact, as the section on judging reports explains.

The T scale: tone (1 to 9)

Tone describes the purity of the CW note. It exists because early transmitters often produced rough, buzzing or unstable signals, and the operator needed to know. The wording still reflects that era of rectified mains power supplies:

Most modern transceivers produce a clean note, so the tone digit is usually 9. When it is not, the fault is more often chirp (the frequency sliding as the key closes) or key clicks (sharp sidebands heard either side of the signal) than hum. ARRL lists old suffixes for these, C for chirp and K for clicks, but operating guides note that few people recognise them today and recommend adding the words CHIRP or CLICKS instead.

A lower T is still worth sending when you genuinely hear a problem. An operator with a failing power supply or a misadjusted amplifier may not know until someone tells them, and a report like 579 with the word CLICKS is more useful than a polite 599.

RST examples: 599, 579, 559 and lower

Reading a report is simply a matter of looking each digit up. These are the reports you will send and receive most often on CW:

Three patterns are worth recognising:

• The first digit matters most. Anything starting with 5 means the other station is copying you fully. A 559 is a perfectly good report; you do not need to be loud to be read.
• A low R with a high S means a problem other than weakness. A report like 359 suggests heavy interference, static crashes or rough sending rather than a weak signal.
• A T below 9 is a hint to check your station. Ask what they hear. If the answer is chirp or clicks, it points to the transmitter, keying or amplifier rather than propagation.

CW reports vs voice reports: RST and RS

The tone digit only makes sense for a keyed carrier, so voice operators use the first two digits only. This two-digit version is usually called an RS report.

On phone the numbers are spoken as separate digits (“five nine”, not “fifty-nine”), and strong signals are often described with a meter reading above S9, as in “five nine plus ten dB”. On CW the report stays within the scale, so the top is 599.

Before RST, operators used Q codes for the same job. ITU-R M.1172 still lists QRK for intelligibility and QSA for strength, each on a 1 to 5 scale, but on CW they have been almost entirely replaced by RST. If you do meet them, remember that QSA stops at 5; “QSA 9” is not a valid report. The Q codes guide covers the codes that are still in everyday use.

5NN and contest reports

In contests, the report is part of a fixed exchange and speed matters more than detail. Two habits follow.

Cut numbers. Contest operators shorten the nines in 599 to the letter N, which keeps the first dah and the final dit of the digit but drops the three dahs in the middle. The receiving station hears letters but writes the digits.

The same trick shortens serial numbers: 0 is commonly sent as T and 1 as A, so an exchange of 599 and serial number 001 might be sent as 5NN TTA. The wider set of CW shortcuts is covered in the abbreviations guide.

Almost everyone gets 599. In most contests the RST is a formality: nearly every station sends 599 whatever the actual signal, because the serial number, zone or location that follows is the information that matters to the log. Some operators call these rubber-stamp reports. This is accepted contest practice, but it means a contest 599 tells you almost nothing about how you really sound.

Outside contests, a real report is more useful and more courteous. If a station is barely readable, a 339 tells them to keep things short and repeat important details.

How to judge a report honestly

RST is subjective. Two operators listening to the same signal on different receivers, antennas and noise levels can give different reports, and both can be right for their location.

Readability: judge by ear

Only you know how easily you are copying. Ask yourself one question: how much of this am I getting? Then use the R table above. This digit needs no equipment and is always worth getting right.

Strength: S-meter or ear

S-meters are convenient but vary widely between receivers. The IARU Region 1 technical recommendation for S-meters defines S9 on HF as an input of -73 dBm (50 microvolts into 50 ohms), with each S unit representing 6 dB, but many receivers are not calibrated to that standard, and the reading also depends on your antenna, preamplifier and attenuator settings. The same signal may read S7 on one radio and S9 on another.

If you have no meter, or do not trust it, judge by ear. The system’s author intended exactly that: his aim was a strength report that meant the same whatever kind of receiver the listener used. Compare the signal with the strongest and weakest stations you hear on the band and place it on the 1 to 9 scale.

Tone: listen to the note

Send 9 unless you hear something wrong. If the note sounds rough, hums, slides in frequency or is surrounded by clicks, lower the digit and say why in plain words.

Checklist before you send a report

1. Did I copy everything? That settles R.
2. How does this signal compare with others on the band right now? That gives S.
3. Is the note clean? That gives T.
4. Would a word such as QSB (fading), QRM (interference) or CLICKS help explain it?

How to send an RST report in Morse code

In a normal CW contact the report goes in your first full over, straight after the greeting, usually introduced with UR RST (your RST) and sent twice so a burst of noise cannot wipe it out:

A typical first over from the station answering a call looks like this, with example call signs:

G4XYZ DE K1ABC TNX FER CALL UR RST 579 579 NAME JIM JIM QTH BOSTON BOSTON HW CPY? G4XYZ DE K1ABC K

The other operator then replies with a report of their own, often starting with a thank-you for yours:

K1ABC DE G4XYZ R TNX FER RPRT UR RST 449 449 QSB NAME ANN ANN QTH YORK YORK HW? K1ABC DE G4XYZ K

Here Ann’s 449 plus the Q code QSB tells Jim that his signal is readable but fading. Some practical points:

1. Send the digits cleanly. Every digit is five elements long, and 7, 8 and 9 differ only in how many dahs come before the dits, so they are easy to confuse at speed if your spacing is rushed. Leave full letter gaps between digits.
2. Repeat the report in a ragchew contact. In a contest, send it once and let the other station ask for a repeat if needed.
3. Add a word when the numbers are not enough: QSB for fading, QRM for interference, QRN for static, CHIRP or CLICKS for signal faults.
4. Say thank you for the report with TNX FER RPRT, but you do not need to repeat their report back.

The rest of the contact, and how the pieces fit together, is explained in the guide to what CW is in ham radio. To hear any report line before you send it on the air, type it into the Morse Code Translator and press Play.

Practise copying report digits

Signal reports are mostly digits, and numbers are where many newcomers slow down. The trainer below plays single digits and you type each one; aim to recognise it as soon as you hear it rather than counting dits and dahs. Switch the practice set to letters plus numbers to mix in N, T and A, the letters used as cut numbers, and use a 20-item session as a quick daily check.

Once 5, 7 and 9 come without hesitation, a report such as 579 will read as one familiar pattern.

Where the RST system came from

RST was proposed by Arthur Braaten, W2BSR, in the October 1934 issue of QST, in an article titled “A New Standard System of Reporting Signals”. He argued that the reporting codes amateurs were using at the time mixed up audibility and readability, so reports contradicted each other, and he offered separate scales for readability, signal strength and tone instead.

His original strength scale had only five steps; it was later widened to the nine steps used today. The ARRL’s Communications Manager urged amateurs to adopt the system in the same issue, and RST became the standard way to report CW signals.

The underlying idea has not changed in over 90 years: say how well you are copying, how strong the signal is and how clean it sounds, in three digits that any operator in any language can understand.

Common RST mistakes

• Sending 599 to everyone outside a contest. It is not wrong, but it wastes the one piece of technical feedback a contact contains.
• Giving a low R to a strong signal without a reason. If you are copying everything, it is R5, even if the band is noisy.
• Confusing RS and RST. On voice there is no T digit; on CW there is.
• Using S-meter readings as absolute truth. Calibrations differ between receivers; treat the meter as a guide.
• Lowering T for fading or noise. Tone is about the transmitted note only. Fading belongs in R or a QSB comment.