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How to read FT8 messages: what CQ, the numbers and RR73 mean

FT8 messages are short on purpose: a whole conversation fits into six 15-second turns. Once you know the pattern, every line on the screen makes sense.

The short version

An FT8 contact trades just enough to prove two stations heard each other: callsigns, a location (a four-character grid square), a signal report in decibels, and a confirmation. Every message fits one fixed-size packet sent in a 15-second time slot, so the words are abbreviated to the bone.

A complete contact, line by line

Here is a typical exchange between two made-up stations, K1ABC in Connecticut and W9XYZ in Indiana:

Messages always put the station being called first and the sender second. So when you see W9XYZ K1ABC -15, K1ABC is talking to W9XYZ.

The pieces

• CQ: "calling anyone." A few letters after it narrow the call: CQ DX wants distant stations, CQ NA wants North America, and CQ POTA is someone operating from a park for the Parks on the Air program.
• Callsigns: the station IDs issued by each country. The first letters tell you the country: K, N, W and AA-AL are the United States, VE is Canada, G is England, JA is Japan, VK is Australia.
• Grid squares such as FN31: the Maidenhead Locator System. The two letters pick a field 20 degrees of longitude by 10 of latitude; the two digits narrow it to a square about 2 degrees by 1 (roughly 100 by 70 miles in the mid-latitudes).
• Reports such as -15: the signal-to-noise ratio in decibels, measured the way FT8 software does, against the noise in a 2,500 Hz band. Most reports run from about -24 (barely decodable) to +10 or so (very strong). Negative numbers are normal: FT8 is built to work below the noise you can hear.
• R in front of a report (R-12): "roger, I got your report, and here's yours."
• RR73 or RRR: "roger roger," which completes the contact. 73 is old telegraph shorthand for "best regards."
• <...> in angle brackets: a callsign the software has only as a short code (used for longer callsigns such as portable ones). It fills in once the full callsign has been received.

The columns on the screen

FT8 software such as WSJT-X lists each decode with a few numbers in front:

• UTC: the start of the 15-second slot the message came from.
• dB: the signal-to-noise ratio, as above.
• DT: the time offset in seconds between your clock and the sender's signal. Values near zero are normal; if everything is off by a second or more, your computer's clock needs setting. FT8 needs clocks accurate to about a second.
• Freq: the audio pitch in hertz where the signal sits within the band's 3 kHz slice. It shows where to find that station on the waterfall.

Special cases you'll see

• Two messages on one line, separated by a semicolon, such as K1ABC RR73; W9XYZ <VP8ABC> -08: a DXpedition (a group operating from a rare place) finishing one contact and starting the next in the same slot. This is WSJT-X's "Fox and Hound" mode.
• Free text such as TNX FB QSO: up to 13 characters of anything, used for short courtesies.
• Contest messages add a serial number or a state or section to the exchange.

Where to watch FT8 happen

The busiest frequencies are 14.074 MHz (20 meters, the best all-round band in daylight) and 7.074 MHz (40 meters, best in the evening), set to upper sideband. Others are 3.573, 10.136, 18.100, 21.074, 24.915, 28.074 and 50.313 MHz. Listening and decoding need no license; any shortwave receiver with SSB, or an SDR, plus free software such as WSJT-X will do.

Want to hear it first? The FT8 signal page has a real recording and its waterfall. Its quicker cousin is FT4.

Further reading

• WSJT-X User Guide
• Franke, Somerville and Taylor, "The FT4 and FT8 Communication Protocols", QEX 2020
• ARRL: the Maidenhead grid locator system