When two amateur radio stations make contact, one of the first things they exchange is a signal report. Rather than trying to describe signal quality in free-form words across potentially noisy, weak, or multilingual paths, the hobby settled long ago on a compact three-digit code: RST. It stands for Readability, Strength, and Tone, and it works the same way everywhere on the planet.
R — Readability (1–5)
Readability describes how well you can actually understand the content of the received signal — not how loud it is, but how intelligible it is.
| Code | Meaning |
|---|---|
| R1 | Unreadable — cannot make out anything |
| R2 | Barely readable — only occasional words distinguishable |
| R3 | Readable with considerable difficulty |
| R4 | Readable with practically no difficulty |
| R5 | Perfectly readable |
Readability is independent of strength. A very strong signal can still score R3 if it is heavily distorted, overdeviated, or buried in interference. Conversely, a weak but clean signal might still earn R4.
S — Strength (1–9)
Signal strength reflects how powerful the received signal is at your location. Many modern receivers include an S-meter on the front panel or in software that displays this value directly, typically calibrated so that S9 corresponds to 50 µV at the antenna input (on HF).
| Code | Meaning |
|---|---|
| S1 | Faint — barely perceptible |
| S2 | Very weak |
| S3 | Weak |
| S4 | Fair |
| S5 | Fairly good |
| S6 | Good |
| S7 | Moderately strong |
| S8 | Strong |
| S9 | Extremely strong |
Above S9, strength is often expressed in decibels over S9: “S9 plus 20 dB” or just “20 over S9”. This is common on the higher HF bands when nearby stations are running high power.
T — Tone (1–9)
The Tone component is only used for CW (Morse code) transmissions. It describes the audio quality of the carrier — whether the note sounds pure and clean or rough and buzzy. A poor tone usually points to problems in the transmitter’s power supply filtering or keying circuit.
| Code | Meaning |
|---|---|
| T1 | Extremely rough, hissing note |
| T2 | Very rough AC note, no trace of filtering |
| T3 | Rough AC note, rectified but not filtered |
| T4 | Rough note, some trace of filtering |
| T5 | Filtered rectified AC, strongly ripple-modulated |
| T6 | Filtered tone, definite trace of ripple modulation |
| T7 | Near pure tone, trace of ripple modulation |
| T8 | Near perfect tone, slight trace of modulation |
| T9 | Perfect tone — no trace of ripple or modulation |
For phone (SSB, FM, AM) contacts, the T component is simply omitted.
How It’s Used in Practice
Phone (Voice) Contacts
On SSB or FM, only R and S are used. The report is spoken as two digits:
“W1ABC, this is OH2DQH. Thanks for the call — you are five nine.”
“Five nine” (59) is by far the most common report heard on the bands. It means perfectly readable and extremely strong. Whether that is always accurate is another question — experienced operators sometimes joke that the real meaning of “59” is simply “I heard you.”
CW (Morse Code) Contacts
All three components are sent. The classic contest-style exchange looks like this:
W1ABC DE OH2DQH UR RST 599 599 BK
“599” means perfect readability, extremely strong signal, perfect tone. In fast contest operation it is sometimes sent as 5NN where N substitutes for 9 because it is faster to key.
Special Suffixes
After the three digits, additional letters can be appended to flag specific problems:
| Suffix | Meaning |
|---|---|
| C | Chirp — slight frequency variation on keying |
| K | Key clicks — sharp interference caused by abrupt CW keying |
| X | Instability — frequency drifting or unstable carrier |
| Q | QSB — signal is fading |
For example, 599K means a perfect signal except for noticeable key clicks from the transmitter’s keying waveform.
A Practical QSO Example
Here is what the RST exchange looks like in a typical HF contact:
- W1ABC calls CQ: “CQ CQ CQ, this is Whiskey One Alpha Bravo Charlie, W1ABC, calling CQ and standing by.”
- OH2DQH responds: “W1ABC, this is OH2DQH. Good morning, thanks for the call. You are 5 and 8 here in Finland. Back to you.”
- W1ABC replies: “OH2DQH, thank you. You are 5 and 7 here in Massachusetts. Nice to meet you — 73.”
Both stations now have a concrete, comparable record of propagation conditions on that path at that moment, using numbers that mean the same thing regardless of what languages the two operators speak.
Why RST Still Matters
The RST system dates back to the early days of amateur radio and has remained essentially unchanged because it does its job elegantly: three numbers, universally understood, no translation needed. Whether you are working a DX station on 20 metres, exchanging a contest log entry on 40, or making your first CW contact on 80, RST gives you an instant shared vocabulary for the most basic question in radio: how am I getting in?
73 de OH2DQH.