RST code

The RST code is used to describe the readability, strength and tone of a signal. The code consists of three digits, the first one represents the readability, the second one represents the strength and the last one the tone.


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