OnAirDecode NDB with an SDR
NDB: the Morse identification of a long-wave navigation beacon.
- Group
- Aviation
- Start frequency
- 0.35 MHz
- In the mode list
- Ident, 190-535 kHz
What NDB is
Non-directional beacons are long-wave radio beacons, usually between 190 and 535 kHz (some sit higher), used for navigation. Each sends its identification in Morse code at about 7 words per minute.
Frequencies and settings
| Start frequency | 0.35 MHz |
|---|---|
| Tuning range of the mode table | 0.19 to 0.535 MHz |
| Sample rate asked | 256 ksps |
| Lowest working rate | 48 ksps |
| Channel width | 10 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 Ident, 190-535 kHz.
What OnAir shows
NDB (non-directional beacon) on long wave, 190-535 kHz: the Morse ident of an aeronautical beacon (a keyed 400 Hz or 1020 Hz tone, or a keyed carrier, about 7 WPM). Receive only. Not the HF beacon list.
Limits and what it was checked with
Checked with generated signals and impairments; recordings of real signals welcome.
Which radio you need
This mode is on low frequencies (below 1 MHz), which many radios do not reach. An SDRplay, an Airspy HF+ or an RTL-SDR in direct-sampling mode can; a long wire or a loop antenna matters more than the radio.
Receiving and the law
Questions about NDB
Can I decode NDB with an RTL-SDR?
Only in direct-sampling mode, which OnAir offers in the radio settings, and the signal may be weak or absent. SDRplay and Airspy HF+ radios reach low frequencies directly.
Is it legal to receive NDB?
Receiving aircraft broadcasts is legal in many countries, but some restrict listening to or using what you hear. OnAir is a receiver. Check the rules where you live.
Can I try NDB 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.