When transmitting or receiving, it is very useful to be able to give and receive useful and consistent signal reports. It helps to guide how to conduct the contact. To achieve this, a system known as the RST reporting system is normally used.
As the name indicates, the RST reporting system is based around three numbers. One is for Readability (R), one is for Strength (S), and one is for Tone (T). The tone is only used for Morse code transmissions.
The meanings for the different numbers are given in the table below:
2 Barely readable
3 Readable with difficulty
4 Readable with little difficulty
5 Perfectly readable
S1 Barely detectable
2 Very weak signals
3 Weak signals
4 Fair signals
5 Fairly good signals
6 Good signals
7 Moderately strong signals
8 Strong signals
9 Very strong signals
T1 Extremely rough note
2 Very rough note
3 Rough note
4 Fairly rough note
5 Note modulated with strong ripple
6 Modulated note
7 Near DC note but with smooth ripple
8 Near DC note but with trace of ripple
9 Pure DC note
As an example, a voice or "fone" signal may be given a report of 4 and 7 if the signal is readable with a little difficulty and is moderately strong. A Morse signal that is totally readable, strong, and has a pure dc note would be given a report 589.
Many receivers incorporate strength or "S" meters and these can be very helpful when trying to judge the strength of a station. The meters are calibrated in "S" units up to S9 and then beyond that they are calibrated in decibels over S9. However it should be remembered that S meters are notoriously inaccurate and should only be used as a guide.