HYPERBOLIC RADIONAVIGATION SYSTEMS
Loran, Decca, Omega, and are hyperbolic radionavigational systems. Hyperbolic navigation patterns are created by a baseline between two transmitters, with each transmitter emitting radio waves toward one another. Where the radio waves intersect and have a constant difference of distance from the two transmitters a locus of points is established. At the midpoint of the baseline is a perpendicular line created by this locus of points called the centerline. As we approach either transmitter, the subsequent hyperbolic lines become curved toward that transmitter, creating the overall pattern. Because radio transmissions are constant in reception, the pattern they form can be determined and a chart overprint created for the purposes of navigation. Each hyperbolic line will represent a specific point on the pattern which can be used by navigators for ascertaining a line of position coinciding with and drawn parallel to that hyperbolic line.
The distance between each hyperbolic line represents a specific distance in nautical miles known as the gradient. The baseline may be extended beyond the transmitter; signals received on the baseline extension are not accurate and should not be used for navigational purposes. The most accurate fixes are along the baseline at the centerline. Each radionavigational system establishes its hyperbolic pattern in a separate manner. In the case of Loran, the time difference between received signals creates the pattern. In the case of Omega and Decca, it is phase comparison that is the prime factor. Phase comparison is a method in which the difference in received cycles of radio waves is measured at their reception point.
Once the hyperbolic pattern is established, a series of transmitters can create additional patterns with these patterns crisscrossing an area. The use of two or more patterns and the subsequent lines of position determined from them allows the navigator to fix a position. It should be kept in mind that radionavigational receivers are like all other radio receivers with system signals subject to the forces and errors that affect all radio transmissions
