Ham Radio Signal Reports: The Complete Guide to Sending and Receiving RST Reports

This complete guide covers everything from the basics of the RST system to advanced digital reporting networks, helping both new licensees and experienced operators get far more out of every QSO signal report they give or receive.

What Are Ham Radio Signal Reports?

Definition and Purpose of Signal Reports in Amateur Radio

One of the most basic features of an amateur radio contact (QSO) is an exchange of signal reports so each participant knows how well they are coming through. A signal report is a standardized numerical code that describes the quality, strength, and (for CW) tonal purity of the signal being received at the other station's location. Rather than saying "you sound pretty good" or "your signal is a bit weak," amateur radio operators use a precise, universally understood shorthand.

The RST system is used by amateur radio operators, shortwave listeners, and other radio hobbyists to exchange information about the quality of a radio signal being received. The RST system is a three-digit number, with one digit each for conveying an assessment of the signal's readability, strength, and tone. This brevity matters enormously during DX pileups, contests, or emergency nets where time is limited and clarity is essential.

Why Accurate Signal Reports Matter for the Ham Radio Community

Accurate signal reports serve several practical purposes that go well beyond politeness. They help you identify problems with your transmitter or antenna, evaluate the effectiveness of your feedline, and understand how propagation conditions are affecting your station's performance on a given band and direction. In general, give accurate reports. Don't write what you think the ham wants to hear. It's helpful to tell someone if their signal isn't coming through clearly.

If you receive a three for readability, you might decide to repeat important things, like your location, or spell out your name to help folks understand you. If you receive a low S number, you might note the time of day, what frequency you're using, and the space weather. In this way, honest signal reports feed directly into better operating decisions.

Brief History of the RST System

In 1934, Arthur Braaten developed the RST code as a systematic way to give feedback. The RST codes provide a nuanced report in just two or three numbers. Before that, various signal reporting systems were in use, including the QSA (signal strength) and QRK (readability) codes used in commercial and maritime radio. The RST system combined readability and signal strength into a single compact exchange while adding tone quality — a critical metric in the early days when most operators built their own transmitters.

The tone report goes back to the early days of radio when most hams were building their own transmitters for Morse code from spare parts — with varying results. The science of radio was still poorly understood, and RST reports helped radio operators significantly. Old radios (and some modern ones) suffered from "ripple" (from ineffective capacitors in the power supply, which are used to filter the rectified AC sine wave into a DC voltage). This was heard in the transmitted CW tone.

Understanding the RST System

Readability: The R Scale Explained (1 to 5)

The Readability (R) component of the RST system focuses on assessing the clarity and ease with which a radio transmission can be understood. It considers factors such as the presence of noise, interference, or fading that may affect the overall intelligibility of the message. The readability scale ranges from 1 to 5, with 1 being the lowest and 5 being the highest.

The five readability levels translate to real-world operating conditions as follows:

R1 — Unreadable: The signal is present but no intelligible content can be copied.
R2 — Barely readable: Barely readable, occasional words distinguishable.
R3 — Readable with considerable difficulty: Usable copy but requires concentration and frequent repeats.
R4 — Readable with practically no difficulty: Good copy with occasional missed words.
R5 — Perfectly readable: Every word is clear with no difficulty.

Factors which impact on readability include QRN (atmospheric noise, static crashes), QSB (fading), and QRM (man-made noise, e.g., plasma TV noise). Most productive QSOs happen at R3 or above, though digital modes like FT8 can complete a contact at readability levels that would be hopeless on voice.

Signal Strength: The S Scale Explained (1 to 9)

The second digit in the RST system denotes the strength of the received signal. It measures the power level of the signal as received by the operator's equipment. The range for the Signal strength (S) scale varies from 1 to 9. The full scale from the official RST definitions runs:

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

S9 is already a very strong signal, but to describe larger signals, steps of 10 dB are used instead of 6 dB, such as S9+20, meaning 20 dB above S9. You will commonly hear experienced operators on the HF bands say things like "you're 20 over S9" on a crowded 20-meter net when a local station is running high power.

Tone: The T Scale for CW and Digital Modes (1 to 9)

The T, or tone factor, refers to the sound qualities of the received CW signal. This nine-point scale rates the purity of the audio tone produced by a CW transmitter, from a harsh 60-cycle AC buzz at T1 all the way to a perfectly clean, pure tone at T9. The full scale runs:

T1 — Sixty cycle A.C. or less, very rough and broad.
T2 — Very rough A.C., very harsh and broad
T3 — Rough A.C. tone, rectified but not filtered
T4 — Rough note, some trace of filtering
T5 — Filtered rectified A.C. 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.

Modern transceivers from quality manufacturers almost always produce T9 tones by default. Additional suffix codes can flag specific problems: for example, 599K indicates a clear, strong signal but with bothersome key clicks. 599C indicates chirp.

How RST Combines Into a Complete Signal Report

The standard signal reporting method for amateur radio is the RST (Readability-Signal Strength-Tone) system. The best signal report for CW operation is RST 599. On phone, we drop the reading for Tone and just give RS reports, so a perfect signal on phone is RS 59 or just "five nine." The three numbers are always read in order: Readability first, then Signal Strength, then Tone (for CW only). On voice modes, you give two digits; on CW and most digital modes, you give three.

Common RST Report Examples and What They Mean

59 (Five Nine): Perfect SSB or FM phone signal — perfectly readable and extremely strong.
57 (Five Seven): A 55 or 57 report indicates that the signal is very readable but the signal strength is not as strong as a 59 signal.
44: Readable with difficulty at only fair strength — likely a weak DX station under marginal conditions.
599: Perfect CW signal — perfectly readable, extremely strong, pure tone.
339: CW signal that is readable with considerable difficulty, weak, but with a good tone — possibly a QRP station at the edge of range.
579K: Good CW signal with a tone quality issue — specifically key clicks.

How S-Meters Work and What They Actually Measure

The Technical Basis of S-Meter Readings

An S meter (signal strength meter) is an indicator often provided on communications receivers, such as amateur radio or shortwave broadcast receivers. Its purpose is to indicate the relative strength of signals passing through your receiver. S-meters are not intended to be absolute value measuring instruments, according to most radio manufacturers, as there are so many factors that can affect meter readings.

In 1981, the International Amateur Radio Union (IARU) Region 1 agreed on a technical recommendation for S-meter calibration of HF and VHF/UHF transceivers. IARU Region 1 Technical Recommendation R.1 defines S9 for the HF bands to be a receiver input power of -73 dBm. This is a level of 50 microvolts at the receiver's antenna input assuming the input impedance of the receiver is 50 ohms.

S-Units and Decibels: Understanding the Relationship

The recommendation defines a difference of one S-unit as a difference of 6 decibels (dB), equivalent to a voltage ratio of two, or power ratio of four. This means that doubling the signal voltage at your antenna terminal moves your S-meter by exactly one S-unit — or that quadrupling the signal power achieves the same result. In practical terms, this means that going from 100 watts to 400 watts will improve your signal report by roughly one S-unit at the receiving station.

If each S-unit adds or subtracts 6 dB by convention, a signal of S1 would be 48 dB lower than S9. Subtracting 48 dB, the signal at S1 would be -121 dBm. The same IARU Region 1 recommendation defines S9 for VHF/UHF to be a receiver input power of -93 dBm. This is the equivalent of 5 µV in 50 Ω. This is an important distinction: an S9 for HF is not the same as S9 for VHF.

Why S-Meter Readings Vary Between Radios

There is considerable variation in S-Meter calibration, so signal reports can vary from radio to radio. Most of the currently popular amateur radio HF rigs, as well as rigs that were sold over the last decade or two, are only calibrated at the S9 point of the scale. This leaves some room for error. As the meter moves above or below S9, the accuracy diminishes. Usually the readings are reasonably acceptable between S6 and S9, but most readings below S5 are off.

This is why you should treat S-meter readings as a useful guide rather than a precise measurement instrument. Two different radios listening to the same signal may give reports that differ by one or even two S-units, especially at weak signal levels. The subjective readability component of the RST report is often more useful than the S-meter reading alone because it reflects what the operator actually hears regardless of calibration errors.

How to Use Your S-Meter Effectively During a QSO

With both CW and SSB, the S-Meter will be bouncing around a bit, so some interpretation is required. For SSB voice, it is standard practice to read peak S-meter deflection on the loudest syllables of speech. For CW, read the peak deflection during each element. Note the average reading during a transmission rather than chasing the peaks and nulls caused by QSB fading. Most S-Meters show an extended scale above S9 that is listed in terms of decibels. The scale may be marked with +10 dB, +20 dB, etc., indicating that the signal strength is that much stronger than S9.