Long range navigation utilizing VLF transmissions

The highly stable propagation characteristics of VLF transmissions make them an ideal source of world-wide navigation data. The arrival phase of a VLF signal is continuously compared with a local standard. The change in the phase difference between the received signal and the local standard is converted to relative motion with respect to the VLF transmitter. Very low frequency transmissions form the basis of a very accurate long range navigation system. The characteristic of these transmissions that make them ideal for such a use is that their arrival phase at a point distant from the transmitter is both stable and predictable.