OnAirDecode LBJ with an SDR
LBJ: railway train warning broadcasts (821 MHz).
- Group
- Cellular & rail
- In the mode list
- Train warning, 821 MHz
What LBJ is
LBJ is the Chinese railway train broadcast: FM on a UHF warning channel (about 821.2375 MHz) carrying 1200 bit/s FSK frames with a train number, a kilometre marker and locomotive data.
Frequencies and settings
| Tuning range of the mode table | 821 to 821.5 MHz |
|---|---|
| Sample rate asked | 960 ksps |
| Lowest working rate | 256 ksps |
| Channel width | 35 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 Train warning, 821 MHz.
What OnAir shows
LBJ (Chinese railway train proximity warning) on about 821.2375 MHz: FM voice channel with 1200 bit/s FSK data for train number, kilometre marker, locomotive ID, direction and speed (receive only).
Limits and what it was checked with
Checked with generated signals and impairments; recordings of real signals welcome.
Which radio you need
This mode sits at a high frequency, so check that your radio tunes it: a HackRF covers 1 MHz to 6 GHz, and RTL-SDR stops near 1.7 GHz. Some modes at these frequencies also need a fast radio (10 to 20 Msps) or a dish and an LNB.
Receiving and the law
Questions about LBJ
Can I decode LBJ with an RTL-SDR?
Probably not: an RTL-SDR tunes up to about 1.7 GHz. A HackRF (1 MHz to 6 GHz) or another wideband radio is the usual choice for this frequency range.
Is it legal to receive LBJ?
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 LBJ 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.