RST

From HFUnderground

The RST system is a standardized way for amateur radio operators (hams) to describe the quality of a radio signal during reception. It is generally used for voice (phone) communications modes (AM, FM, and SSB), Morse code (CW), and some digital modes.

• R (Readability): A scale from 1 to 5 that indicates how understandable the signal is, with 5 being perfectly readable and 1 being unreadable.
• S (Strength): A scale from 1 to 9 that measures the strength of the received signal, with 9 being extremely strong and 1 being very faint.
• T (Tone): Used only for CW (Morse code) or digital modes, it ranges from 1 to 9, describing the quality of the signal tone, with 9 being pure and stable.

An RST report might look like "599," which means perfectly readable, very strong signal, and pure tone. It’s a quick and efficient way to communicate signal quality during contacts.

Modified versions of the RST and SIO systems are sometimes used by operators on the various CB radio services, other license-free, specialized use and land mobile two-way radio services such as the VHF MURS service, VHF marine band radio, the UHF FRS, GMRS and similar VHF/UHF services.

See also: SINPO and SIO.