In the early days of amateurradio the RST-system was defined as following:
READABILITY (R) also known as "RADIO"
   
1
- Unreadable
2
- Barely readable, occasional words distinguishable
3
- Readable with considerable difficulty
4
- Readable with practically no difficulty
5
- Perfectly readable
   
  SIGNAL STRENGTH (S)
   
1
- Faint signals, barely perceptible
2
- Very weak signal
3
- Weak signal
4
- Fair signal
5
- Fairly good signal
6
- Good signal
7
- Moderatly strong signal
8
- Strong signal
9
- Extremly strong signal
   
TONE (T) only used in CW (continous wave = morse telegraphy),
transmissions, now also in use for digital modes
   
1
- Sixty-cycle ac or less, very rough and broad
2
- Very rough ac, very harsh and broad
3
- Rough ac tone, rectified but not filtered
4
- Rough note, some trace of filtering
5
- Filtered rectified ac but strongly ripplemodulated
6
- Filtered tone, definite trace of ripple modulation
7
- Near pure tone, trace of ripple modulation
8
- Near perfect tone, slight trace of modulation
9
- Perfect tone, no trace of ripple of modulation of any kind
 
Note: no tone-report for speech transmissions
 
(Source: The ARRL handbook for radio amateurs 1992; ARRL = American Radio Relay League)

 

NRRL

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