RST stands for Readability, Strength and Tone in amateur radio circles. Readability is on a scale of 1-5 (best), while strength and tone are on a scale of 1-9 (best). When communicating in voice mode, you only use the readability and strength; in morse code, you add in the tone. A perfect signal report would be 599.

The RST system is used by radio amateurs as a formalized way of giving information on the quality of the signal they receive (signal reports). An RST is a number consisting of three digits, which are transmitted during the conversation, and written on the QSL card in the cases where the amateurs exchange such cards afterwards. The digits give information on the readability, strength and tone of the signal, respectively. The tone part of the signal report is used only for modes that can be said to have a tone, such as CW (morse code), RTTY, PSK, and so forth, but not for telephony.

Although the conventional descriptions quoted in the list below suggest that the difference between the digits are clearly defined (sort of like the Beaufort scale or the Mohs hardness scale, the ratings a radio amateur gives out to a fellow radio amateur's transmission is very subject to individual judgment.

Readability means how well you are able to understand what the other amateur is saying (or sending). Here, 1 is the worst, and 5 is the best.
  • 1--Unreadable
  • 2--Barely readable, occasional words distinguishable.
  • 3--Readable with considerable difficulty.
  • 4--Readable with practically no difficulty.
  • 5--Perfectly readable.

Signal Strength means how much the received signal stands out from the background noise. Many radios have so-called "S-meters", and some operators just report the number the needle stands on when it peaks. This is not a very good idea, since these instruments are not standardized from manufacturer to manufacturer, and since background noise alone may add as much as 5 to the reading. Therefore, as earlier mentioned, this is not something you should read out on instruments, but something you should judge with your ears.

  • 1--Faint signals, barely perceptible.
  • 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--Extremely strong signals.

Tone, on CW, means how the transmitted tone sounds. The tone should sounds as much like a perfect sine wave as possible.

  • 1--Sixty cycle a.c or less, very rough and broad.
  • 2--Very rough a.c., very harsh and broad.
  • 3--Rough a.c. tone, rectified but not filtered.
  • 4--Rough note, some trace of filtering.
  • 5--Filtered rectified a.c. but strongly ripple-modulated.
  • 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 or modulation of any kind.

The signal report is almost always given very early in the QSO, before the exchange of name and QTH, and before any rag chewing. On CW, or digital modes where text is transmitted (such as RTTY) the standard formula for reporting the RST is, for example UR RST RST 557 557, or UR RST RST IS 439 439. On phone modes (SSB or FM), the most widely used phrase is "you're five and nine here".

Note that the tone part of the signal report is not applicable in telephony modes, and must always be omitted. Such signal reports with only two digits are sometimes called "RS". QSL cards for SSB or FM QSOs with 3 digit RSTs are judged as invalid for use as proof in contests and applications for diplomas.

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