The R-S-T system is used by

amateur radio operator An amateur radio operator is someone who uses equipment at an amateur radio station to engage in two-way personal communications with other amateur operators on radio frequencies assigned to the amateur radio service. Amateur radio operators ...

s, 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, Cairo, 1938.

Readability

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 Morse code is a telecommunications method which Character encoding, encodes Written language, text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code i ...

telegraphy Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas pi ...

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 The human voice consists of sound made by a human being using the vocal tract, including talking, singing, laughing, crying, screaming, shouting, humming or yelling. The human voice frequency is specifically a part of human sound produ ...

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.The beginner's handbook of amateur radio by Clay Laster, Page 379, McGraw-Hill Professional, 2000, , # Unreadable # Barely readable, occasional words distinguishable # Readable with considerable difficulty # Readable with practically no difficulty # Perfectly readable

Strength

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. # Faint—signals barely perceptible # Very weak signals # Weak signals # Fair signals # Fairly good signals # Good signals # Moderately strong signals # Strong signals # Extremely strong signals For a quantitative assessment, quality HF receivers are calibrated so that S9 on the S-meter corresponds to a signal of 50 μV at the antenna standard terminal impedance 50 ohms. One "S" difference should correspond to 6 dB at signal strength (2x voltage = 4x power). On VHF and UHF receivers used for weak signal communications, S9 often corresponds to 5 μV at the antenna terminal 50 ohms. Amateur radio (ham) operators may also use a signal strength of "20 to 60 over 9", or "+20 to +60 over 9." This is in reference to a signal that exceeds S9 on a signal meter on a HF receiver.

Tone

The T stands for "Tone" and is measured on a scale of 1 to 9. Tone only pertains to Morse code and other digital transmission modes and is therefore omitted during voice operations. With modern technology, imperfections in the quality of transmitters’ digital modulation severe enough to be detected by human ears are rare. 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.

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

decibel The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a Power, root-power, and field quantities, power or root-power quantity on a logarithmic scale. Two signals whos ...

s, in excess of "S9", displayed on the receiver's S meter. Example: "Your signal is 30 dB over S9," or more simply, "Your signal is 30 over 9." 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. 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 PSK31 or "Phase-shift keying, Phase Shift Keying, 31 Baud", also BPSK31 and QPSK31, is a popular computer-sound card-generated radioteletype mode, used primarily by amateur radio operators to conduct real-time keyboard-to-keyboard Synchronous co ...

or RTTY.

References

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External links

Ham Radio RST Signal Reporting System for CW Operation
by Charlie Bautsch, W5AM
RSQ - An Improved Signal Reporting System for PSK
Amateur radio Encodings Operating signals Telecommunications-related introductions in 1934