RST Signal Report
Three digits that describe how you are being heard. Pick them apart once, and 599 stops being a ritual.
599
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 signals, barely perceptible. |
|---|---|
| S2 | Very weak signals. |
| S3 | Weak signals. |
| S4 | Fair signals. |
| S5 | Fairly good signals. |
| S6 | Good signals. |
| S7 | Moderately strong signals. |
| S8 | Strong signals. |
| S9 | Extremely strong signals. |
Tone
| T1 | 60 Hz AC or less, very rough and broad. |
|---|---|
| T2 | Very rough AC, very harsh and broad. |
| 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. |
Three separate judgements
RST is not one number but three, and they measure different things:
- R - readability, from 1 to 5. Can the message be copied? This is the only part that says whether the contact works at all.
- S - strength, from 1 to 9. How much signal arrives. On most receivers this is simply what the S-meter shows; one S-unit is meant to be 6 dB.
- T - tone, from 1 to 9, and only in Morse. How clean the note sounds.
A signal can be strong and unreadable - that is a 259, and it usually means interference. It can also be faint and perfectly readable, 519, which is the everyday experience of anyone running low power.
Why the T scale reads like a museum guide
Read the tone scale and you are looking at the history of transmitters. T1 is "60 Hz AC or less, very rough and broad" - a note straight off the mains, because early transmitters rectified their power without smoothing it. T5 is filtered but still ripples. Only T9 is the pure note that any modern radio produces without effort.
Which is why the T is almost never anything but 9 today. It is a scale for a problem that has been solved. It survives because a distorted signal still needs a way to be described - a chirp when the key goes down, a hum from a failing power supply.
Why everyone sends 599
In a contest the exchange has to be short and identical every time, so the report is a formality: 599, sent as 5NN with cut numbers, whether the signal deserves it or not. Both operators know it means nothing. What counts is the serial number or zone that follows.
Outside contests it is worth being honest. A real report tells the other station something they cannot know otherwise - that their antenna is working, that their keying has a chirp, that they are readable at 100 milliwatts. That is information; 599 is punctuation.
Frequently asked questions
-
Why is there no T in phone reports?
Because tone describes the quality of a keyed carrier, which voice does not have. On phone the report is two digits, RS - "you are five nine".
-
What are cut numbers?
Shortened digits used in fast exchanges: N for 9, T for 0, and sometimes A for 1 or E for 5. 5NN is 599. They are shorter to send and are expected in contests, but they have no place in a callsign or a serial number that matters.
-
Is S9 a fixed amount of signal?
On a properly calibrated HF receiver, S9 corresponds to 50 microvolts at 50 ohms. In practice receivers vary widely, so S readings are comparable within one station and not much beyond it.
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Can I give 599 if the signal is weak?
In a contest, yes, everyone does. In an ordinary contact it wastes the one chance to tell the other operator something useful.