OnAirDecode JT9 with an SDR
JT9: narrow weak-signal amateur contacts.
- Group
- Amateur: digital
- Start frequency
- 14.078 MHz
- In the mode list
- WSJT, 14.078 MHz
What JT9 is
JT9 is a weak-signal digital mode of the WSJT family, decoded by the same receiver as FT8.
Frequencies and settings
| Start frequency | 14.078 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, 14.078 MHz.
What OnAir shows
JT9 weak-signal contacts (9-FSK, convolutional code, 60 s periods, 15 Hz wide), 14.078 MHz.
The mode's own tab has these views: Decodes, Map. The other tabs (Overview, Receiver, Scan, History) are described on the main window page.
Limits and what it was checked with
Checked with generated signals and impairments; recordings of real signals welcome.
Which radio you need
This is a shortwave mode, so the radio has to tune HF. An SDRplay, Airspy HF+ or an RTL-SDR in direct-sampling mode do that directly; with a HackRF an HF upconverter or a direct-sampling receiver is the usual route. A long wire or loop antenna matters more than the radio.
Receiving and the law
Questions about JT9
Can I decode JT9 with an RTL-SDR?
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.
Is it legal to receive JT9?
Amateur radio signals are meant to be received. Receiving needs no licence in most countries; OnAir does not transmit.
Can I try JT9 in OnAir without a radio?
Yes. Most modes include a built-in synthetic test signal, so you can open the screen and try the controls before you own a radio.