OnAirMaritime · Experimental
Decode Weather fax with an SDR
OnAir receives Weather fax. HF weather fax (radiofax): weather charts for ships on upper sideband.
What Weather fax is
HF weather fax stations broadcast weather charts and satellite pictures as slow analogue fax signals, mostly for ships.
Frequencies and where it is used
NAVTEX, DSC, weather fax.
In OnAir the tuning shortcut is Weather charts, HF; you can enter any frequency your radio reaches.
What OnAir shows for Weather fax
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 Weather fax
Can I decode Weather fax 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 Weather fax?
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 Weather fax 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.