For an ADF receiver and the NDB to be reliable, what should be confirmed?

When using an ADF (Automatic Direction Finder) receiver and an NDB (Non-Directional Beacon), confirming that the Morse code identifier is heard and the bearing pointer is stable is essential for reliable operation. The Morse code identifier provides an audible confirmation that the ADF is tuned to the correct NDB frequency and that the signal is being received properly.

A steady bearing pointer indicates that the receiver is locked on to the correct signal without interference or fluctuations, which could lead to navigation errors. This stability is crucial for ensuring accurate navigation and course tracking, especially in challenging environments or during poor weather conditions.

The other options do not adequately ensure reliability. Turning off the ADF would prevent it from functioning, being within 10 nautical miles does not guarantee that the signal is clear or stable, and a clear frequency is important but does not confirm that the correct identifier is received or that the ADF is properly tracking the NDB. Therefore, option B directly addresses the reliability criteria necessary for safe operation.