The RST system
Readability 1–5, Strength 1–9, Tone 1–9 (CW only).
- Readability: 1 unreadable, 3 readable with difficulty, 5 perfectly readable.
- Strength: 1 barely perceptible, 5 fairly good, 9 extremely strong.
- Tone: 9 is pure; lower values indicate hum or ripple, and are rare with modern equipment.
So 59 on voice means perfectly readable, extremely strong. 599 on CW adds perfect tone.
Honesty
In contests and pileups everyone sends 59/599 regardless — it is a ritual, not a measurement. In a ragchew, give a real report; it is genuinely useful to the other operator, especially if they are testing an antenna.
S-units
One S-unit is nominally 6 dB, and S9 is defined as −73 dBm at the receiver on HF. Signals stronger than S9 are reported as "20 over 9" and so on. Real S-meters are not well calibrated and vary enormously between radios.
Common CW and digital abbreviations
| ABT about | ES and | HW how | TNX thanks |
| AGN again | FB fine business | NR number | TU thank you |
| ANT antenna | GM/GA/GE good morning/afternoon/evening | OM old man (any operator) | UR your |
| BK break | HI laughter | PSE please | WX weather |
| CUL see you later | HR here | RIG transceiver | XYL spouse |
| DE from | HV have | RPT repeat | 73 best regards |
Prosigns (CW)
AR end of message · SK end of contact · KN invitation to a specific station only · K invitation to any station · BT separator/pause · AS wait