A-3 Mixed With Noise, Only At Night (AM)

Chart A-3:

Mixed with noise, only at night (AM).

The following factors can be considered as possible causes of noise appearing at night.
Factors due to signal conditions:
Due to the fact that long-distance signals are more easily received at night, even stations that are received without problem during the day may experience interference in a general worsening of 'reception conditions. The weaker station is more susceptible to interference, and a change to a different station or the appearance of a beat sound* may occur.

* Beat sound: Two signals close in frequency interfere with each other, creating a repetitious high-pitched sound. This sound is generated not only by sound signals but by electrical waves as well.