Overview
This lecture covers the principles and operation of Non-Directional Beacons (NDB) and Automatic Direction Finders (ADF), including their uses, limitations, and navigational techniques.
NDB and ADF Basics
- NDB stands for Non-Directional Beacon, a ground-based transmitter that emits radio waves in all directions.
- ADF stands for Automatic Direction Finder, an aircraft instrument that detects NDB signals and points to their direction.
- NDBs are identified by unique frequencies and Morse code signals, shown on VFR/IFR charts.
- Typical NDB frequencies range from 200 to 1,750 kHz.
Operation and Usage
- Pilots tune the ADF to the NDB frequency; the ADF needle points towards the beacon.
- NDBs can have ranges from 20 to 400 nautical miles depending on power and location.
- The ADF system includes a receiver, aerial system (loop and sense antennas), and a cockpit display.
Accuracy and Limitations
- Ideal NDB accuracy is within 2°, but accuracy can be affected by signal interference, terrain, and thunderstorms.
- Thunderstorms can cause the ADF needle to point toward them instead of the NDB, resulting in navigation errors.
- Cross-check the Morse code identification to ensure correct NDB tuning.
Navigation Techniques
- QDM is the magnetic bearing to the NDB; QDR is the magnetic bearing from the NDB.
- Use "push the needle" to correct towards the NDB and "pull the tail" when departing from it in crosswind.
- Tracking to an NDB requires correcting for wind drift by maintaining a wind correction angle for a straight flight path.
- Avoid using commercial radio stations for navigation due to unreliable signal sources.
Key Terms & Definitions
- NDB (Non-Directional Beacon) — A radio transmitter on the ground sending signals in all directions.
- ADF (Automatic Direction Finder) — An aircraft instrument that points to the selected NDB.
- QDM — Magnetic bearing to the NDB station.
- QDR — Magnetic bearing from the NDB station.
- Loop Aerial — A directional antenna used to sense the NDB signal direction.
- Sense Aerial — A non-directional antenna used with the loop aerial to resolve signal ambiguity.
- BFO (Beat Frequency Oscillator) — Adds an audio tone to the NDB signal, making Morse code identification possible.
Action Items / Next Steps
- Review the names of the two antennas in the ADF system that identify NDB signals (loop aerial and sense aerial).
- Prepare for the test by understanding how to identify, tune, and track to/from NDBs.
- Practice wind correction techniques for NDB navigation.