Mode FST4

FST4: slow weak-signal contacts and FST4W beacons.

Group	Amateur: digital
Default frequency	1.8366 MHz
Default sample rate	2 Msps
In the mode list	WSJT, 1.8366 MHz

Step-by-step: Tutorial-FST4

What FST4 is

FST4 (and FST4W) is a weak-signal digital mode of the WSJT family for the low bands.

Frequencies and settings

Setting	Value
Start frequency	1.8366 MHz
Tuning range of the mode table	1 to 30 MHz
Sample rate asked	2 Msps
Lowest working rate	250 ksps
Channel width	3 kHz

OnAir takes any frequency you type; the numbers above are the mode's starting point and the range its table describes. In the app the shortcut label is WSJT, 1.8366 MHz.

What OnAir shows

FST4 and FST4W (15 s to 30 min periods, 4-GFSK, LDPC (240,101) / (240,74)) for LF, MF and HF weak-signal contacts and beacons.

The mode's own tab has these screens: Decodes, Map. The other tabs (Overview, Receiver, Scan, History) are described on the Main window page.

Tips and caveats

• Checked with generated signals and impairments; recordings of real signals welcome.
• Which radio: An RTL-SDR can receive HF only in direct-sampling mode, which OnAir offers in its radio settings; results depend on the antenna. SDRplay and Airspy HF+ radios are better suited.
• Try it without a radio: most modes include a built-in synthetic test signal, so you can open the screen and try the controls first.
• Receiving and the law: Amateur radio signals are meant to be received. Receiving needs no licence in most countries; OnAir does not transmit. See Legal.

Related pages

• All modes, Amateur: digital
• Supported radios, Troubleshooting, FAQ
• More in Amateur: digital: FT8, FT4, FT2, WSPR, JT65, JT9, Q65, MSK144, PSK31, JS8Call, RTTY, CW, SSTV, HamDRM, Olivia, Contestia, MFSK, THOR, DominoEX, Hellschreiber