GB1473937A - Long range marine navigation system - Google Patents

Abstract

1473937 Radio-navigation TEXAS INSTRUMENTS Inc 14 Aug 1974 [20 Aug 1973 22 Aug 1973] 35782/74 Heading H4D Use of a range-range postion finding system, wherein a mobile station 10, Fig. 1, interrogates a plurality of remote stations 11, 12, 13 and the ranges 11a, 12a, 13a are determined from the timings of the resulting responses, is extended to much greater than beyond the horizon distances, by the use of frequencies in the 100 MHz and above range and CHIRP (pulse compression) techniques. At the transmitter 90, Fig. 3, of the mobile station a 0À5 Á sec. transmit command pulse 15, Fig. 2, gates through a 0À5 Á sec. burst of 23À5MHz energy from oscillator 100. This is stretched and frequency modulated into a 15 Á sec. pulse by a first electro acoustic surface wave device 102 and then into a 30 Á sec. pulse 16 (after compensation for attenuation (103)) by a second surface wave device 104. The frequency modulated long pulse is then heterodyned up to the UHF or VHF carrier (switch 112), by various local oscillator and mixing stages (106-110) for transmission by antenna module 92 as a "CHIRP" signal. The repetition period of the "CHIRP" pulses is 3À33 msec. At the remote (fixed) station the receiver 91 (also Fig. 3) receives the "CHIRP" signal 17 via the antenna module 92 and by a series of heterodyning steps and the use of two surface wave devices 139, 141 matched to those at the mobile station transmitter, produces a narrow pulse 18. After envelope detection at 145, a threshold detector 147 and sync-processor 146 produces a 0À5 Á sec. pulse 19 coincident with the centre of the narrow pulse 18, which pulse 19 is fed as the transmit command signal to the transmitter 90 of the remote station, which is as already described for the mobile station. The transmitter of the remote station thus produces a response "CHIRP" signal 20 which on reception by the mobile station produces thereof a corresponding pulse output 24 from gate 148 for use by the time (and range) measure circuit. Such that the receiver of the mobile station "knows" which remote station is transmitting and may be enabled (gated) to receive the response of a selected station only, the transmitter of the mobile station, prior to the transmission of the "CHIRP" pulses transmits a series of coded pulse groups 320a, 320c, 320d, Fig. 12, 10 msec. long and coded such that only base station 11 will respond to group 320a, only base station 12 will respond to group 320c and only base station 13 will respond to group 320d. The respective response coded pulse groups 323a, 325a, 327a are received back at the mobile station (321a, 321b, 321c) and give a course indication of the ranges of the base stations. This enables a series of gates Fig. 3, to be set up for the ensuing "CHIRP" responses, i.e. gate 335 for the response from 11, gate 341 for that from 12, gate 347 for that from 13. The gates can thus follow when the mobile station moves.