Orfordness Beacon

It allowed the angle to the station to be measured from any aircraft or ship with a conventional radio receiver, and was accurate to about a degree.

A second station operating on the same principle was set up to provide wider area coverage and allow two-bearing fixes between Orford Ness and Farnborough Airport.

The angle between the navigator and the beacon can be taken by using a simple mechanism known as a loop antenna which can be rotated around the vertical axis.

As the antenna is rotated, the strength of the received signal varies, and drops to zero (the null) when the loop is perpendicular to the line to the beacon.

Measurements better than a few degrees are difficult with a small antenna, and because of the electrical characteristics, it is not always easy to make a larger version that might provide more accuracy.

The station broadcast a continuous AM longwave signal at 288.5 kHz (1040 m) through a large loop antenna which was mechanically rotated at 1 rpm, or 6 degrees a second.

In practice this is a relatively minor concern, as traditional navigation methods are normally able to resolve this discrepancy – only one of the angles makes sense at a given time.

[5] The original Orfordness Beacon was constructed in a small building that looked similar to the lower portion of a Dutch windmill.