Low-frequency radio navigation system

US4396918A · kind A · utility

Assignee

• The United States of America as represented by the Administrator of the National Aeronautics and Space Administration · US

Inventor

• David E. Wallis · Dubuque, US

Key dates

• Filing date: Mar 6, 1981
• Grant date: Aug 2, 1983
• Expiry date: Mar 6, 2001

Classification

• Technology area (CPC G): Physics
• CPC primary: G01S1/30
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

A method of CW navigation is provided using four transmitters (TR1-TR4) operating at sufficiently low frequencies to assure essentially pure groundwave operation. The transmitters are keyed to transmit constant bursts (1/4 sec) in a time-multiplexed pattern with phase modulation of at least one for identification of the transmitters with the ability to identify the absolute phase of the modulated transmitter(s) and the ability to modulate low-rate data for transmission. The transmitters are optimally positioned to provide groundwave coverage over a service region of about 50.times.50 km for the frequencies selected in the range of 200-500 kHz, but their locations are not critical because of the beneficial effect of overdetermination of position of a receiver (R) made possible by the fourth transmitter. Four frequencies are used, at least two of which are selected to provide optimal lane resolution. All transmitters are synchronized to an average phase as received by a monitor receiver (M).