US 3,997,902 AGranted

Transmission of radio navigation phase corrections

AssigneeSociete d'Etudes, Recherches et Constructions Electroniques Sercel

InventorGeorges Nard

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Abstract

A method of and apparatus for differential mode navigation in a sequential system of radio-navigation by phase reception. A transmitted amplitude-modulated radio-navigation carrier wave is phase or frequency modulated, this modulation being effected by a low-frequency subcarrier signal which is itself so phase modulated sequentially in accordance with phase corrections that each phase correction appears approximately simultaneously with the phase concerned. The phase corrections are derived from the difference between the phase received from each fixed station of the system and theoretical phases which should be received from that station. At a standard radionavigation receiver, the subcarrier signal modulated by the corrections is recovered, and the phase corrections are so applied to the received phases that each phase undergoes the phase correction received at the same instant.

Claims18

Dependent claims

A method of transmitting information to mobile receivers, comprising:

-- sequentially transmitting phase information from at least two fixed stations of a sequential radio-navigation system;
-- receiving at a fixed radio-beacon station said phase information according to a multiplex sequence corresponding to the sequence of transmission of the sequential radio-navigation system, and deriving a phase correction signal linearly related to the difference between the phase received from each fixed station and theoretical phases which should be received from each fixed station, said phase correction signal being also time-multiplexed according to the same said sequence of transmission from the radio-navigation system so that a given phase correction signal is produced approximately simultaneously with the phase information which should be corrected by this correction signal;
-- transmitting from said radio-beacon station an amplitude modulated signal for conventional local direction finding, said signal being also phase modulated according to the multiplexed sequence of phase correction signals;
-- receiving at a mobile receiver said phase information from the fixed stations of the radio-navigation system and receiving also from the fixed radio-beacon station the amplitude modulated signal for conventional local direction finding and phase modulated for phase corrections of the received phase information;
-- filtering and demodulating said signal from the radio-beacon to recover the multiplexed phase correction signal, and applying phase corrections to the received phase information from the fixed stations so that each phase information is modified by the phase correction which is received at the same instant of the multiplexed sequence as said phase information.

2 more elements

A radio-beacon system comprising a first radio-beacon station adapted to transmit a signal which is amplitude modulated for conventional direction finding, said radio-beacon including:

a radiofrequency power amplifier coupled to a transmitting aerial for effecting amplitude modulation of a carrier wave in an all-or-nothing mode as instructed by an identification-code generator circuit;
a receiver for the phase information transmitted from a sequential radio-navigation system supplying received phases, and a sequence format;
means for producing phase corrections from these received phases and from prescribed theoretical phases respectively;
means for producing a low-frequency multiplexed signal having a phase which is so related linearly and in succession to phase correction in accordance with the said sequence format that each phase correction appears approximately simultaneously with the phase to which the correction applies;
and
means for phase modulation of the carrier wave by this multiplexed phase-correction signal, the phase modulated carier wave being applied to the radiofrequency amplifier, and then thereby being transmitted after having further undergone an amplitude modulation.

3 more elements

Dependencies are inferred from the claim text.