RST signal reports explained
Readability one to five, strength one to nine, tone one to nine. Two digits on voice, three on CW.
The short answer
RST stands for readability, strength and tone. Readability runs 1 to 5, strength 1 to 9 and tone 1 to 9, with tone used only on CW. A report of 59 means perfectly readable and extremely strong. On FT8 the report is not RST at all but a signal to noise ratio in decibels, where minus 15 is a strong signal.
- Readability scale
- 1 to 5
- Strength scale
- 1 to 9
- Tone scale
- 1 to 9, CW only
- One S unit
- 6 dB nominally
- S9 reference
- 50 microvolts at 50 ohms
- FT8 report
- dB SNR, not RST
The RST system dates from the 1930s and has survived because it does something useful in two digits: it tells the other operator whether the problem is that you are weak or that something is interfering with the signal. Those are different problems with different responses.
It has also become a formality on voice, where five nine is exchanged reflexively regardless of the actual signal. That is fine in a contest, where the exchange is a formality by design, and it is a lost opportunity in a conversation, where an honest report is the only feedback the other station gets about its antenna.
Readability, the first digit
Readability
The R in RST, scale 1 to 5
| Value | Meaning | What you would say |
|---|---|---|
| 1 | Unreadable | Nothing recoverable at all |
| 2 | Barely readable, occasional words | You are getting one word in five |
| 3 | Readable with considerable difficulty | Following it takes real effort |
| 4 | Readable with practically no difficulty | Perfectly usable, a little noise |
| 5 | Perfectly readable | No effort required |
Readability is about comprehension, not loudness. A weak but clean signal can be R5. A very strong signal covered in interference can be R3.
Strength, the second digit
Strength
The S in RST, scale 1 to 9
| Value | Meaning | Nominal level |
|---|---|---|
| 1 | Faint, barely perceptible | At the noise floor |
| 2 | Very weak | -42 dB relative to S9 |
| 3 | Weak | -36 dB |
| 4 | Fair | -30 dB |
| 5 | Fairly good | -24 dB |
| 6 | Good | -18 dB |
| 7 | Moderately strong | -12 dB |
| 8 | Strong | -6 dB |
| 9 | Extremely strong | 50 microvolts at 50 ohms |
| 9 plus | Above S9, reported in dB | For example 20 over 9 |
One S unit is conventionally 6 dB, and S9 is defined as 50 microvolts across 50 ohms on HF. Very few radios follow either convention accurately, so the same signal reads differently on different receivers. Use the dB and power ratio calculator to convert between S units and decibels.
Tone, the third digit
Tone applies to CW only and describes the purity of the note. Modern transmitters are essentially all T9, which is why the digit is now given as 9 almost universally and why some operators drop it entirely.
- T1 to T4 describe severe hum, roughness and instability, which almost never occurs with modern equipment.
- T5 to T8 describe a note with some ripple or a trace of modulation.
- T9 is a pure, stable, clean note, which is what any current radio produces.
- A genuine report below T9 today usually indicates a power supply problem or a failing final, and it is worth passing on honestly for that reason.
- The occasional suffixes still in use are C for a chirp on keying and K for key clicks, both of which are worth reporting because they annoy everybody on the band.
What a report should tell you
- 59 or 599
- Perfect copy, very strong. Honest when true, and a formality in contests where the exchange is fixed by convention.
- 55
- Perfectly readable, moderate strength. A completely normal report for a typical contact and nothing to be concerned about.
- 33
- Readable with difficulty, weak. This is real information: something in your station or the path is limiting you.
- 52
- Perfectly readable but very weak. A clean signal at low strength, which usually means the path is long rather than that something is wrong.
- 25
- Strong but hard to copy. Something is interfering, or your audio is distorted. Worth investigating, because strength is not the problem.
- 20 over 9
- Twenty decibels above S9. Common on strong local signals and on the low bands at night.
Reports on other modes
By mode
What the exchange is on each mode
| Mode | Report format | Example | Meaning |
|---|---|---|---|
| SSB voice | RS, two digits | 57 | Readable, moderately strong |
| CW | RST, three digits | 579 | Readable, strong, pure note |
| RTTY | RST, three digits | 599 | Tone digit largely vestigial |
| FT8 and FT4 | dB SNR | -15 | Signal 15 dB below noise reference |
| PSK31 | RSQ or dB | 59 or -12 | Varies by operator |
| FM voice | Full quieting or scale | Full quieting | Noise floor fully suppressed |
| DMR and digital voice | Copy or no copy | Full copy | Digital either decodes or does not |
FT8 reports are a signal to noise ratio in a 2.5 kHz reference bandwidth, not RST. Zero would be a signal equal to the noise. Minus 15 is strong, and the decoding floor is around minus 21 to minus 24.
What changes your reports
The things that actually move the needle
In order of effect. The radio is last on this list for a reason.
Easy Up
Easy Up 20 ft telescoping push-up mast
Height. Worth more than power on almost every path, and the cheapest decibels available.
Check price$185.00
JYR
JYR8010 8-band end fed half wave, 150 W
A resonant multiband wire in the clear beats a compromise antenna at any power level.
Check price$89.99
Bolton Technical
Bolton400 low-loss coax, 100 ft with PL-259
Low-loss coax, which costs you nothing on receive as well as transmit.
Check price$119.95
Heil Sound
Heil Pro 7 headset microphone
A proper communications microphone shapes the audio for intelligibility, which raises readability rather than strength.
Check price$457.75
Surecom
Surecom SW-102 digital VHF/UHF SWR meter
Confirms you are actually putting out the power you think you are before blaming the band.
Check price$57.99
AURSINC
NanoVNA H4 vector network analyzer
Shows whether the antenna is resonant where you are calling, which is the usual cause of a disappointing report.
Check price$89.90
Common questions
Questions people ask about this
What does 59 mean?
Readability 5, perfectly readable, and strength 9, extremely strong. On CW it becomes 599 with a tone digit. It is an honest report for a genuinely strong clean signal, and it is also exchanged reflexively in contests where the report is a formality rather than an observation. On a conversational contact, give the report you actually observe.
How much is one S unit?
Nominally 6 dB, with S9 defined as 50 microvolts across 50 ohms on HF. In practice very few radios follow that convention accurately, and the same signal commonly reads two or three S units differently on two receivers. Treat S meter readings as relative indications on your own station rather than as absolute measurements.
Why does everyone give 59 reports?
It started in contests, where the exchange is fixed by convention and nobody has time to assess a signal, and it leaked into general operating. It is harmless in a contest and a lost opportunity in a conversation, since an honest report is the only feedback the other station gets about its antenna and audio. Giving a real report is welcomed far more often than not.
What is the report on FT8?
Not RST at all. FT8 exchanges a signal to noise ratio in decibels referenced to a 2.5 kHz bandwidth, so zero would mean a signal equal to the noise in that bandwidth. Minus 15 is a strong FT8 signal and the decoding floor is around minus 21 to minus 24 depending on conditions. The software generates the number automatically.
What does the tone digit mean and do I need it?
Tone describes the purity of a CW note on a 1 to 9 scale, and modern transmitters are essentially all T9, so the digit carries almost no information now. It is still customary to send it on CW and RTTY. A genuine report below T9 today usually means a power supply fault or a failing final, which is worth passing on plainly.
Keep going
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