Learn the typical NDB range, why some beacons reach farther, and how power, terrain, altitude, night effects and interference alter reception.
An NDB has no single fixed range. In aviation, published service ranges commonly run from about 15 NM for a compass locator to 75 NM for a high-powered beacon. Actual reception depends on transmitter power, frequency, terrain, ground conductivity, aircraft altitude, atmospheric noise, ionospheric conditions and the ADF installation.
How far can an NDB be received?
The governing figure is the charted or officially published coverage for the individual beacon, not simply the distance at which its Morse identifier becomes audible.
The following US classifications provide useful reference figures, although other countries may publish designated operational coverage instead:
| Classification | Transmitter power | Nominal service range |
|---|---|---|
| Compass locator | Under 25 W | 15 NM |
| MH | Under 50 W | 25 NM |
| H | 50–1,999 W | 50 NM |
| HH | 2,000 W or more | 75 NM |
These figures are nominal service ranges, not worldwide limits. Some long-range NDB installations have published coverage beyond 75 NM, while a weak or obstructed beacon may become unreliable sooner. Our explanation of how an NDB signal and the aircraft’s ADF produce a bearing covers the underlying equipment.
What affects NDB range and bearing accuracy?
Usable NDB range is determined by signal strength, propagation and bearing stability together; being able to hear the station does not prove that its indicated bearing is trustworthy.
- Transmitter power and antenna efficiency: Higher power generally extends coverage, but an NDB’s electrically short antenna and local installation also affect how efficiently that power is radiated.
- Frequency: Frequency changes ground-wave attenuation and susceptibility to interference. Power alone therefore cannot predict the range of two different beacons.
- Ground conductivity: Low- and medium-frequency ground waves normally travel farther over conductive seawater or damp ground than over dry, rocky terrain.
- Terrain and buildings: Hills can screen or distort a signal. Reflections and changes in ground conductivity near a coastline can produce coastal-refraction errors, especially when crossing the coast at a shallow angle.
- Aircraft altitude: Climbing often reduces terrain screening and improves reception, but an NDB is not governed by a simple VHF line-of-sight formula. Doubling altitude does not guarantee twice the range.
- Day and night propagation: After dark, ionospheric sky waves can carry an NDB much farther. They can also interfere with its ground wave, causing fading and a wandering needle, so greater reception distance may mean poorer navigation.
- Atmospheric and electrical noise: Thunderstorms, precipitation static and aircraft electrical systems can mask the identifier or deflect the ADF needle. Rain and cloud do not normally attenuate an NDB significantly by themselves; the associated static is the usual problem.
- Receiver and installation quality: ADF sensitivity, antenna condition, wiring and interference from equipment aboard the aircraft all influence the practical range.
VOR and DME behave differently because they use higher-frequency, largely line-of-sight signals. Our comparison of NDB, VOR and DME behaviour explains why their ranges cannot be judged by the same rules.
Can an NDB be used beyond its published range?
An NDB may be receivable beyond its published range, but it should not be treated as a dependable navigation source there unless the applicable procedure explicitly permits it.
- Check the published coverage: Use the figure attached to that beacon or procedure rather than assuming a range from its classification.
- Identify the station: Listen for and verify the complete Morse identifier. A wrong or missing ident means the indication must not be used.
- Watch for instability: Needle hunting, sudden swings and fading suggest interference, terrain effects or night error.
- Cross-check the position: Compare the ADF bearing with another approved navigation source rather than relying on a distant NDB alone.
A mistake we see constantly is treating a clearly audible ident as proof of an accurate bearing. Reception range can be much greater than usable navigation range, particularly at night.
How is NDB range modelled in flight simulators?
Flight simulators may use the beacon’s database range, a simplified signal-strength calculation or a hard reception cut-off, so simulated behaviour will not always reproduce real ground-wave and sky-wave effects.
If an expected NDB cannot be received, check the tuned frequency, station identifier, ADF operating mode, aircraft equipment and distance from the beacon. Navigation-data changes can also remove or replace real-world stations. Our practical VOR and NDB simulator guide covers tuning, identifying and interpreting the instruments without assuming every simulator models propagation identically.