What is meant by the term “night effect”...

🔍 Key Concepts

• ADF (Automatic Direction Finder) always points to the apparent direction of the NDB (Non Directional Beacon) signal, not necessarily the true geographic location if the signal is distorted • How radio waves in the low/medium frequency band behave differently in daytime versus nighttime, especially with the ionosphere changing after sunset • The difference between ground waves (following Earth’s surface) and sky waves (bouncing off the ionosphere) and how that can affect bearing accuracy at night

💭 Think About

• Think about what physically changes in the atmosphere after sunset that could affect how radio signals travel from the NDB to the aircraft • Consider whether the ADF system itself starts transmitting anything, or whether it only receives signals from the NDB • Ask yourself: which option describes an effect that could cause the ADF pointer to give an unreliable or wandering bearing to the station at night?

✅ Before You Answer

• Verify that NDBs normally operate 24 hours a day, not just in daylight • Confirm that an ADF in the aircraft is a receiver, not a transmitter, so any explanation involving ADF ‘transmissions’ should be treated carefully • Check which option correctly involves signal propagation and reflections at night, and could plausibly cause the ADF to point in a misleading direction

What is meant by the term “night effect” when using an aircraft’s Automatic Direction Finding (ADF) equipment? Night effect refers to the fact that:

All Non Directional Beacon (NDB) transmitters are turned-off at dusk and turned-on at dawn.

Non Directional Beacon (NDB) transmissions can bounce -off the Earth’s ionosphere at night and be received at almost any direction.

An aircraft’s ADF transmissions will be slowed at night due to the increased density of the Earth’s atmosphere after sunset.

An aircraft’s ADF antennas usually collect dew moisture after sunset which decreases their effective reception distance from an NDB transmitter.

🔍 Key Concepts

💭 Think About

✅ Before You Answer