OnAirDecode JT4 with an SDR
JT4: EME and weak-signal contacts.
- Group
- Amateur: digital
- Start frequency
- 144.12 MHz
- In the mode list
- EME, 144.120 MHz
What JT4 is
JT4 EME weak-signal contacts (4-FSK, convolutional code, 47 s transmissions, sub-modes A to G).
Frequencies and settings
| Start frequency | 144.12 MHz |
|---|
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 EME, 144.120 MHz.
What OnAir shows
JT4 EME weak-signal contacts (4-FSK, convolutional code, 47 s transmissions, sub-modes A to G).
Limits and what it was checked with
Checked with generated signals and impairments; recordings of real signals welcome.
Which radio you need
Any radio that tunes this range works. An RTL-SDR covers roughly 24 MHz to 1.7 GHz, and every other radio in the radio guide reaches it too. Antenna height and a clear view of the transmitter matter most.
Receiving and the law
Questions about JT4
Can I decode JT4 with an RTL-SDR?
Usually yes for narrowband signals, as an RTL-SDR tunes roughly 24 MHz to 1.7 GHz at up to about 2.4 Msps. Wide signals such as TV channels need a faster radio, and OnAir says next to the source what the selected radio can do.
Is it legal to receive JT4?
Amateur radio signals are meant to be received. Receiving needs no licence in most countries; OnAir does not transmit.
Can I try JT4 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.