At what time of day is the ADF 'Night effect' error most pronounced?

The ADF "Night effect" error is most pronounced during twilight. This phenomenon occurs because, at twilight, there are changes in ionospheric propagation conditions due to the sun's position relative to the horizon. During these times, the long-wave signals that the ADF (Automatic Direction Finder) uses can be influenced by atmospheric conditions, resulting in erratic navigation indications.

During twilight, the lower frequencies can experience significant reflection from the ionosphere, leading to multiple signals being received. This can create confusion, causing the ADF to point inaccurately as it may pick up signals that come from different directions due to these reflections, resulting in navigation errors.

While at night, the ADF still experiences some degree of error due to similar atmospheric conditions, the effects are often less pronounced compared to twilight when the transition between day and night creates the most unstable propagation conditions. Similarly, daytime conditions tend to stabilize these signals, reducing the likelihood of the "Night effect" interference. Thus, twilight is the time when the ADF's reliability is notably compromised.