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On which bearings do the errors caused by the shoreline/coastal effect reach their maximum?
  • A
    Bearings 0° to 30° to the coastline.
  • B
    Bearings perpendicular to the coastline.
  • C
    Any bearing in the HF band.
  • D
    Bearing 30° to 60° to the coastline.

Refer to figure.
Radio waves speed up over water due to the reduced absorption of energy (attenuation) compared to that which occurs over land. This speeding up causes the wave front to bend (refract) away from it’s normal path and pull it towards the coast.

Refraction is negligible at 90 degrees to the coast(perpendicular to shoreline) but increases as the angle of incidence decreases. As seen in the figure the refraction of the radio waves is at it’s maximum from 0 – 30 degrees from the shoreline.

Therefore if there is a NDB station near to the coast, most erroneous readings occur when you are at acute angles.

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