Loading…
Signal reports: RS, RST and the S-meter
How to tell someone how well you hear them, in numbers.
How to tell someone how well you hear them, in numbers.
A signal report tells the other operator how well you copy them. It is the one piece of information every contact is expected to exchange. Phone uses two numbers (RS); CW and digital text modes use three (RST).
| Digit | R: readability | S: strength | T: tone (CW) |
|---|---|---|---|
| 1 | Unreadable | Faint, barely perceptible | Very rough, like a 60 Hz hum |
| 2 | Barely readable, occasional words | Very weak | Very rough AC tone |
| 3 | Readable with considerable difficulty | Weak | Rough AC tone, unfiltered |
| 4 | Readable with practically no difficulty | Fair | Rough, some trace of filtering |
| 5 | Perfectly readable | Fairly good | Filtered, but strong ripple |
| 6 | Good | Filtered, definite ripple | |
| 7 | Moderately strong | Near-pure tone, trace of ripple | |
| 8 | Strong | Near-perfect tone | |
| 9 | Extremely strong | Perfect, pure tone |
Read it as a sentence: "you're 5 by 9" means perfectly readable and extremely strong. On CW, a report of 599 is "perfect on everything". A weak signal with a clean tone, copied with effort, might be 339.
In practice 59 (and 599) is given to almost everyone, especially in contests, where the exchange must be fast. Treat that as a polite formality. In an ordinary QSO, an honest report ("I'm copying you 4 by 6, with some QSB") is much more useful, and worth giving when conditions are marginal. Digital modes such as FT8 are different: the software sends the received signal-to-noise ratio in dB, which is a real measurement.
The S meter on a receiver measures signal strength. One S unit is 6 dB, a factor of four in power. Above S9 the scale is read in dB: "20 over nine" means 20 dB stronger than S9. A common calibration, the amateur HF convention, puts S9 at 50 µV across 50 Ω, which is −73 dBm; the usual VHF/UHF convention puts it 20 dB lower, at −93 dBm.
| Reading | Level (HF convention) | Voltage at 50 Ω |
|---|---|---|
| S1 | −121 dBm | 0.2 µV |
| S3 | −109 dBm | 0.8 µV |
| S5 | −97 dBm | 3.2 µV |
| S7 | −85 dBm | 12.6 µV |
| S9 | −73 dBm | 50 µV |