Select ALL correct statements about NDB signals and their use.

NDBs operate in the low- and medium-frequency bands, and the aircraft uses an ADF to receive them. Their signals can propagate as ground waves and sky waves. At night, sky-wave effects can cause increased range, fading, and bearing errors, so the claim of immunity is incorrect.\n\n**Key takeaway:** NDB reception is useful but can be affected by propagation conditions.\n\n**Glossary:** **Ground wave**: signal travelling near Earth's surface; **sky wave**: signal propagated via the ionosphere.