OnAirCellular & rail · Experimental
Decode GSM-R with an SDR
OnAir receives GSM-R. Railway GSM base stations (GSM-R, 921 - 925 MHz): cell identity, location area, operator, channel lists (receive only, public broadcast).
What GSM-R is
GSM-R is the railway version of GSM, around 921 to 925 MHz in Europe, used for train control and communication.
Frequencies and where it is used
Railway GSM broadcast (BCCH, 921 - 925 MHz).
In OnAir the tuning shortcut is Railway, 921 - 925 MHz; you can enter any frequency your radio reaches.
What OnAir shows for GSM-R
Base stations: ARFCN, BSIC, cell identity, location area, operator code, channel lists; band scan; receive only.
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
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.
Questions about GSM-R
Can I decode GSM-R 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 GSM-R?
OnAir only reads the public broadcast information of cells and base stations, and does not decrypt or follow any user traffic. Check the rules where you live.
Can I try GSM-R 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.