👂 The RST System: Reporting Signal Quality
The RST (Readability, Strength, Tone) system is a three-digit code used by amateur radio operators to give a quick, standardized report on the quality of a received signal. It is an efficient way to let the sending station know exactly how their transmission is being received, especially when operating Morse Code (CW) or Single Sideband (SSB).
The Three Components of RST
The report consists of three numbers, always given in the order of R-S-T.
1. Readability (R) — Scale 1 to 5
Readability indicates how easy it is to understand the signal, regardless of its volume or quality.
| Score | Meaning |
| R1 | Unreadable |
| R2 | Barely readable, occasional words distinguishable |
| R3 | Readable with considerable difficulty |
| R4 | Readable with practically no difficulty |
| R5 | Perfectly readable |
2. Signal Strength (S) — Scale 1 to 9
Signal Strength is a measure of the signal’s electrical power at the receiver, typically indicated by an S-meter on the radio. It is often the highest number reported.
| Score | Meaning |
| S1 | Faint signals, barely perceptible |
| S3 | Very weak signals |
| S5 | Fairly good signals |
| S7 | Moderately strong signals |
| S9 | Extremely strong signals (usually full-scale) |
Note: S9 is the top of the scale, but hams sometimes report signals “S9 + 10dB” (or more) to indicate the signal strength goes beyond the S9 calibration.
3. Tone (T) — Scale 1 to 9 (Primarily for CW/Digital)
Tone describes the quality of the signal’s electrical carrier, originally developed for Morse Code (CW) and digital modes. For modern SSB voice transmissions, the Tone value is typically omitted or automatically reported as 9.
| Score | Meaning |
| T1-T4 | Very rough, chirpy, or filtered AC notes |
| T5-T8 | Modulated, key clicks, or slightly rough DC notes |
| T9 | Perfectly pure DC note |