RST code

Raffaello Tesi

The RST code, where the acronym stands for  Readability-Strength-Tone, is used by amateur radio operators, shortwave listeners, and other radio hobbyists to exchange information about the quality of a radio signal being received.

Readability (R) Signal strength (S) Tone (T)
1. Unreadable 1. Faint signal, barely perceptible 1. Sixty cycle a.c or less, very rough and broad
2. Barely readable, occasional words distinguishable 2. Very weak 2. Very rough a.c., very harsh and broad
3. Readable with considerable difficulty 3. Weak 3. Rough a.c. tone, rectified  but not filtered
4. Readable with practically no difficulty 4. Fair 4. Rough note, some trace of filtering
5. Perfectly readable 5. Fairly good 5. Filtered rectified a.c. but strongly ripple-modulated
6. Good 6. Filtered tone, definite trace of ripple modulation
7. Moderately strong 7. Near pure tone, trace of ripple modulation
8. Strong 8. Near perfect tone, slight trace of modulation
9. Very strong signals 9. Perfect tone, no trace of ripple or modulation of any kind


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