What RST means
RST stands for Readability, Strength and Tone. It is a three-digit code amateurs use to tell another station how their signal sounds. The system was devised in the 1930s and is still the standard way to exchange reports on CW. A phone (voice) report leaves out the tone digit, so it has just two digits.
RST chart
Readability (R), 1 to 5
| Value | Meaning |
|---|---|
| 1 | Unreadable |
| 2 | Barely readable, occasional words distinguishable |
| 3 | Readable with considerable difficulty |
| 4 | Readable with practically no difficulty |
| 5 | Perfectly readable |
Strength (S), 1 to 9
| Value | Meaning |
|---|---|
| 1 | Faint signals, barely perceptible |
| 2 | Very weak signals |
| 3 | Weak signals |
| 4 | Fair signals |
| 5 | Fairly good signals |
| 6 | Good signals |
| 7 | Moderately strong signals |
| 8 | Strong signals |
| 9 | Extremely strong signals |
Tone (T), 1 to 9 (CW and other keyed or digital signals only)
| Value | Meaning |
|---|---|
| 1 | Sixty-cycle AC or less, very rough and broad |
| 2 | Very rough AC, very harsh and broad |
| 3 | Rough AC tone, rectified but not filtered |
| 4 | Rough note, some trace of filtering |
| 5 | Filtered rectified AC but strongly ripple-modulated |
| 6 | Filtered tone, definite trace of ripple modulation |
| 7 | Near pure tone, trace of ripple modulation |
| 8 | Near perfect tone, slight trace of modulation |
| 9 | Perfect tone, no trace of ripple or modulation of any kind |
The tone descriptions date from the days of rough analog transmitters. Modern rigs rarely produce a tone bad enough to hear, so a tone report below 9 is unusual today.
Phone reports
On voice, you give two digits: readability and strength. “You are five nine” means perfectly readable and very strong. A weaker but understandable signal might be “four five.”
CW reports and 599
On CW you add the tone digit. “599” means perfectly readable, extremely strong, perfect tone. Because it is the top of every scale, it is often sent routinely, especially in contests. That is why a 599 does not always say much about a real signal, a point covered under honest reporting below.
Suffix letters
Historically, letters were added to the end of a CW report to flag specific problems:
| Suffix | Meaning |
|---|---|
| X | Exceptionally stable, crystal-controlled |
| C | Chirp |
| D | Drift |
| K | Key clicks |
For example, “599K” means a strong, readable signal with key clicks. These suffixes are rarely used now but you may still hear them.
S-meter and “over S9”
Most receivers have an S-meter, and the strength digit is often read from it. A common calibration convention is that one S-unit equals 6 dB, and that S9 on HF corresponds to a signal of about 50 microvolts at the antenna input (about 5 microvolts on many VHF and UHF receivers). Real radios vary, and many meters are not precisely calibrated, so treat the number as an estimate.
Signals stronger than S9 are reported in decibels over S9, for example “20 over nine” or “30 over S9.”
Cut numbers in contests
In CW contests, operators often send the letter N instead of 9, because it is quicker in Morse. A report of 599 becomes “5NN.” This is called a cut number. See our CW abbreviations guide for other CW shorthand.
Digital modes and RTTY
Yes, RTTY is still used, particularly in contests, and a 599 report is commonly exchanged in RTTY contests. For many other digital modes, operators exchange numeric reports measured by the software (for example, signal-to-noise ratio in decibels) rather than RST. An RSQ system, which replaces tone with a quality digit, has also been proposed for some digital modes.
Giving honest reports
- Listen before you answer; do not default to 599 unless it is true.
- On a casual voice contact, a real report helps the other station adjust their antenna or power.
- During contests, 59 or 599 is expected, and the exchange is mostly a formality.
- If a signal is weak, plain words such as “you are weak but copyable” can be as useful as numbers.
Related Q signals
QSA (strength) and QRK (readability) are Q signals that serve a similar purpose. See our guide to Q signals for ham radio for more.