OnAirDecode VDL4 with an SDR
VDL Mode 4: synchronization and DLS bursts, CPR positions when decoded in the clear.
- Group
- Aviation
- In the mode list
- STDMA link, 136.9 MHz
What VDL4 is
VDL Mode 4: STDMA GFSK data link on 118 to 137 MHz (synthetic + spec; receive only).
Frequencies and settings
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 STDMA link, 136.9 MHz.
What OnAir shows
VDL Mode 4: STDMA GFSK data link on 118 to 137 MHz (synthetic + spec; receive only).
Limits and what it was checked with
Checked with generated signals and impairments; recordings of real signals 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.
Receiving and the law
Questions about VDL4
Can I decode VDL4 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 VDL4?
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 VDL4 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.