The RST system is used by Radio Amateurs, shortwave listeners, and other radio hobbyists to exchange information about the quality of a radio signal being received. The code is a three digit number, with one digit each for conveying an assessment of the signal's readability, strength, and tone. The code was developed in 1934 by Amateur radio operator Arthur W. Braaten, W2BSR, and was similar to that codified in the ITU Radio Regulations in 1938.
Word of Caution
On more than one occasion I have 'upset' another operator by refusing to give them a 59 or 599 report, despite what they think I should be hearing/receiving them.
"Listen very carefully, I shall say this only once"....I will ONLY give a report as I hear them and only as I hear them, I do not care what another operator thinks I should hear, I will ONLY report on what I hear/receive.
I would expect the same courtesy in return, I know and fully expect that my signal will not always be a “very strong signal”, it will not always be “perfectly readable”, and, certainly won't always have a “perfect tone”, so please only give me a correct RST!
Readability (R)
The R stands for “Readability”. Readability is a qualitative assessment of how easy or difficult it is to correctly copy the information being sent during the transmission. In a Morse code telegraphy transmission, readability refers to how easy or difficult it is to distinguish each of the characters in the text of the message being sent; in a voice transmission, readability refers to how easy or difficult it is for each spoken word to be understood correctly. Readability is measured on a scale of 1 to 5.
1. Unreadable.
2. Barely readable, occasional words distinguishable.
3. Readable with considerable difficulty.
4. Readable with practically no difficulty.
5. Perfectly readable.
Strength (S)
The S stands for “Strength”. Strength is an assessment of how powerful the received signal is at the receiving location. Although an accurate signal strength meter can determine a quantitative value for signal strength, in practice this portion of the RST code is a qualitative assessment, often made based on the S meter of the radio receiver at the location of signal reception. “Strength” is measured on a scale of 1 to 9.
1. Faint signal, barely perceptible.
2. Very weak.
3. Weak.
4. Fair.
5. Fairly good.
6. Good.
7. Moderately strong.
8. Strong.
9. Very strong signals.
For a quantitative assessment, quality HF receivers are calibrated so that S9 on the S-meter corresponds to a signal of 50μV at the antenna terminal. On VHF and UHF receivers used for weak signal communications, S9 often corresponds to 5μV at the antenna terminal.
Tone (T)
The T stands for “Tone”. Tone is ONLY used in Morse code and digital transmissions and is therefore omitted during voice operations. With modern transmitter technology, imperfections in the quality of the transmitter modulation that can be detected by humans are rare. Tone is measured on a scale of 1 to 9.
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.
Suffix Codes
Suffixes were historically added to indicate other signal properties, and might be sent as 599K to indicate a clear, strong signal but with bothersome key clicks.
A. Signal distorted by auroral propagation.
C. "Chirp" (frequency shift when keying).
K. Key clicks heard.
M. Signal distorted by multipath propagation.
S. Signal distorted by scatter propagation.
X. Stable frequency (crystal control.)
Variations
An example RST report for a voice transmission is “59”, usually pronounced “five nine” or “five by nine”, a report that indicates a perfectly readable and very strong signal. Exceptionally strong signals are designated by the quantitative number of decibels, in excess of “S9”, displayed on the receiver’s S meter. Example: “Your signal is 30dB over S9.”
Because the N character in Morse code requires less time to send than the 9, during amateur radio contests where the competing amateur radio stations are all using Morse code, the nines in the RST are typically abbreviated to N to read 5NN. In general, this practice is referred to as abbreviated or “cut” numbers.
RSQ
The RSQ system has also been proposed for digital modes as an alternative to the RST system. The Q replaces "Tone" with "Quality" on a similar 1-9 scale indicating presence or number of unwanted 'sidebar pairs' in a narrow-band digital mode, such as PSK31 or RTTY
Updated 12 April 2022.