FT8, FT4, MSK144, Q65 and JT65

Lets cover off the most popular ones under the hood of the WSJT-X application, the most popular being FT8. They all rely on you PC clock to be aligned to NTP as they operate on a time-slots for transmit and receive. Depending on the mode, the time-slot length varies.
 

These are all weak signal modes. They are optimised to work in challenging conditions and as a result are generally narrow bandwidth and have high degrees of in-built error correction.

They are based around standard communications words/phrases and this is hard-coded into the mode itself.
i.e. they are designed to efficiently get across the minimum of information in the most efficient way. That will generally be a quick exchange of Callsigns, locators and signal reports with the luxury of giving a 73s at the end.  As a result, operating these modes is almost automatic and via preset macros with little scope for a general conversation.

If you are the sort of ham who likes a long chat, then these particular modes are definitely not for you. If you are using modes such as JT9 or J65, a QSO just to exchange callsigns, locators and signal reports can take 5 or 6 minutes.

I have a number of the FT and JT series modes covered below. Others are available for esoteric operating scenarios. You can read about the full suite on the WSJT-X introduction.

 

FT8
- The most popular mode. Designed for the exchange of callsigns, grid locators, reports etc
- Operates in 15 second Rx/Tx time-slots

- Occupied BW is 50 Hz

- 8 CPFSK carriers 6.5Hz apart

- Effective data rate is just 5 words per minute
- S/N decode down to -21dB
- External PDF specification for The FT4 and FT8 Communication protocols

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FT4
- Contesting based mode. Faster than FT8 but not as robust
- Operates in 7.5 second Rx/Tx time-slots

- Occupied BW is 83.3 Hz

- 4 CPFSK carriers 20.8Hz apart

- Effective data rate is 12.5 words per minute
- S/N decode down to -17.5dB
- External PDF specification for The FT4 and FT8 Communication protocols

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MSK144
- VHF/UHF Meteor Scatter mode
- Operates in 15 second Rx/Tx time-slots

- Occupied BW is 2.5kHz

- 2 MFSK carriers 1kHz apart

- Effective data rate is 2000 bits per second using 144 bit long packets
- External PDF specification for the MSK144 Protocol for Meteor-Scatter Communication

 

Q65
- Tailored for VHF and higher bands for Tropospheric/Ionospheric scatter and EME modes 
- Operates in 15/30/60/120/300 Second time slots

- Occupied BW is 433Hz, 217Hz. 108Hz, 49Hz and 19Hz depending on time-slot period.

- External PDF specification for the Quick-Start Guide to Q65

JT65 (3 sub modes A, B and C)
- Tailored for extremely weak signals optimised for VHF EME modes 

- Operates in 60 Second time slots
- Each message (in a 60 second slot) can contain no more than 13 characters

- Occupied BW of 180Hz, 360Hz or 710Hz depending on which sub-mode of JT65 you choose

- 65 carriers either 2.7Hz, 5.4Hz or 10.8Hz apart depending on which sub-mode of JT65 you choose
- External PDF specification for The JT65 Communications Protocol

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Below is a typical waterfall display showing multiple FT8 QSOs occurring. The waterfall shows rolling time on the Y-Axis and frequency on the X-Axis.

What you are looking at is a spectrum display of the received audio channel. In the example below, it is looking at 2kHz of bandwidth. You can clearly see multiple QSOs scrolling down the screen and the horizontal green lines you see breaking up the QSO segments are the 15 second time-slots for FT8.