OnAirMaritime · Experimental
Decode DSC with an SDR
OnAir receives DSC. DSC digital selective calling: distress alerts and calls, MF/HF and VHF channel 70.
What DSC is
Digital Selective Calling is the maritime distress and calling system on VHF and HF: a short digital burst that alerts and addresses ships and coast stations.
Frequencies and where it is used
NAVTEX, DSC, weather fax.
In OnAir the tuning shortcut is Ship calls, 2187.5 kHz; you can enter any frequency your radio reaches.
What OnAir shows for DSC
Safety messages, distress and calling, fax pictures.
This receiver is built from the published specification and checked end to end on simulated signals. It has had little or no testing on real transmissions yet, so reports and recordings on Discord are 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.
Questions about DSC
Can I decode DSC 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 DSC?
Receiving ship and coast-station broadcasts is legal in many countries, with limits on using or passing on private traffic. OnAir is a receiver. Check the rules where you live.
Can I try DSC 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.
Try it without a radio
OnAir includes built-in synthetic test signals for most modes, so you can open this screen, see the layout and try the controls before you own a radio. The Tour button walks you through the app.