- The RST Code is used to report on the quality of a radio signal that is being received …
- R = Readability – this is an assessment of how hard or easy it is to correctly copy the information being sent during the transmission
- S = Signal Strength – this indicates how powerful the received signal is at the receiving location
- T = Tone – used only in Morse code and digital transmissions, it describes the quality of the transmitter’s modulation. While this part of the RST Code is still in use, its relevance has diminished as modern transmitter technology can generally be expected to deliver high tonal quality signals
| Readability | |
| R1 | Unreadable |
| R2 | Barely readable, occasional words distinguishable |
| R3 | Readable with considerable difficulty |
| R4 | Readable with practically no difficulty |
| R5 | Perfectly readable |
| Signal Strength | |
| S1 | Faint signal, barely perceptible |
| S2 | Very weak |
| S3 | Weak |
| S4 | Fair |
| S5 | Fairly good |
| S6 | Good |
| S7 | Moderately strong |
| S8 | Strong |
| S9 | Very strong signals |
| Tone | |
| T1 | Extremely rough hissing note |
| T2 | Very rough AC note, no trace of musicality |
| T3 | Rough AC tone, rectified but not filtered |
| T4 | Rough note, some trace of filtering |
| T5 | Filtered rectified AC but 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 of any kind |
- example: 59 = “perfectly readable, very strong signals” (voice)
- example: 44 = “readable with practically no difficulty, fair signals” (voice)
- example: 589 = “perfectly readable, strong signals, perfect tone …” (Morse)