dari https://www.essexham.co.uk/ft8-basics-explained

FT8 – The Basics Explained
In 2017, FT8 started to become the most popular of the various data modes. At the time of writing (Feb 2018), it appears to be the most popular for a number of reasons:

It’s fairly simple to set up
It’s significantly faster than the similar JT-65
It works very well even with a lot of noise
It’s popular, so there’s lots of activity
It’s semi-automated, making for easy contacts
It’s a great way of racking up the countries you’ve worked, without too much hassle
As with modes such as JT65 and PSK31, you interface your HF rig to a computer, and send out text encoded by your computer over the amateur bands. With FT8, you’re restricted to very small messages, with a limit of 13 characters per message.

Here is a typical conversation over FT8:

“CQ M6PSK JO01” CQ call from M6PSK
“M6PSK G0QQQ IO81” G0QQQ replies with their location
“G0QQQ M6PSK -12” M6PSK responds with a signal report
“M6PSK G0QQQ R-08” G0QQQ confirms signal report & replies with his own report
“G0QQQ M6PSK RRR” M6PSK says Reception Report Received
“M6PSK G0QQQ 73” G0QQQ says Best regards
“G0QQQ M6PSK 73” M6PSK says Best regards
Each message of up to 13 characters takes 13 seconds to send. There are 4 slots per minute, and you transmit for one 15 second block, then listen for replies for 15 seconds, and transmit again for 15 seconds. The exchange above would therefore take about 90 seconds (compared with seven minutes on JT65).