GB2093310A

GB2093310A - Navigation System Receiver

Info

Publication number: GB2093310A
Application number: GB8204427A
Authority: GB
Original assignee: Philips Gloeilampenfabrieken NV
Current assignee: Koninklijke Philips NV
Priority date: 1981-02-18
Filing date: 1982-02-15
Publication date: 1982-08-25
Also published as: IT8219667A0; GB2093310B; DK65682A; IT1149652B; AU8051082A; NL8101720A; DE3204591A1; FR2500170A1; NO820450L; SE8200881L

Abstract

A receiver for a navigation system such as the "Decca Navigator" system comprises an aerial (1), an aerial filter (2), a buffer amplifier (3) and a plurality of tuned amplifiers (4, 5, 6 and 7). Two balanced demodulators (8-1, 8-2), which are each controlled by two local oscillator signals of opposite phases, are connected to the output of each amplifier. The two signals (0 DEG , 180 DEG ) which control one demodulator (8-1) are in a ninety degrees phase relationship to the signals (90 DEG , 270 DEG ) which control the other demodulator (8-2). These signals are derived from a frequency synthesiser (12) which is connected to a non-synchronized source of local oscillator signals (13). Low-pass filters (14, 15) are connected to the outputs of the demodulators. The outputs of said low-pass filters are connected to a signal multiplexer (16), the output of which is connected to a A/D-converter (17). The output of said converter is connected to a processor (18). The processor converts the information of the navigation signals into position co- ordinate information. Display means (19) shows the position information in longitude and latitude. The receiver does not require a synchronised local oscillator. <IMAGE>

Description

SPECIFICATION A Receiver for Use in a Navigation System The invention relates to a receiver for use in a navigation system, comprising a plurality of spaced transmitters transmitting synchronized navigation signals at at least one predetermined channel frequency and in a predetermined time sequence, the receiver comprising a source of local oscillator signals at the said predetermined channel frequency and mixing means for mixing the received navigation signals with the local oscillator signals operable for providing signals representing the quadrature components of the beat frequency signal between the received navigation signals and the local oscillator signals.

Such a receiver is disclosed in United Kingdom Patent Specification 1086,733. This receiver is intended for use in a- radio navigation system in which a master station and a red, green, and purple slave station transmit, one after the other and between the continuous transmissions at different channel frequencies, what are commonly referred to as multi-pulses which comprise a combination of signals at the frequencies 6F, 8F, 9F and 5F, wherein F is a frequency in the region of 14 kHz. This prior art receiver receives signals at one frequency, namely at the channel frequency 6F.Said receiver comprises a synchronized local oscillator which is synchronized by the transmit signal from the master station, which station continuously transmits, except during the multiple pulses, a signal at the frequency 6F, at which the oscillator can lock.

Synchronizing the local oscillator complicates the receiver. This complication becomes more important when the receiver not only receives signals at the frequency 6F, but is also extended for the reception of signals at the frequencies 8F, 9F and 5F.

It is an object of the invention to provide a receiver which does not require a synchronized local oscillator and which can be realized in a simple manner, using standard components.

The receiver in accordance with the invention is therefore characterized in that the mixing means comprise two balanced demodulators, each demodulator being controlled by two local oscillator signals having opposite phases, said signals being derived from a frequency synthesizer which is connected to a nonsynchronizing source of local oscillator signals and the two signals controlling one demodulator being in a ninety degrees phase relationship to the two signals controlling the other demodulator, and that low-pass filters are connected to the outputs of the demodulators and the outputs of said low-pass filters are connected to respective input of a signal multiplexer the output of which is connected to an analog-to-digital converter, the output of which is connected to a programmable data processor for converting the information of the navigation signals into output signals representing the position coordinates of the receiver, and display means for displaying the position coordinates under the control of these output signals.

The invention will now be further described with reference to an embodiment shown in the sole Figure of the accompanying drawing.

The receiver comprises an aerial band-pass filter 2 connected to the aerial 1 The aerial is actually part of the filter which has four resonances at the channel frequencies 6F, 8F, 9F and 5F. At the frequency 7F there is a notch to suppress signals at 1 OOkHz, which originate from LORAN-C chains.

The amplifiers 4, 5, 6 and 7, which are respectively tuned to the frequencies 6F, 8F, 9F and 5F, are driven by a buffer amplifier 3 which is connected to the aerial filter 2. The received signals can be switched off in the buffer amplifier 3 in order to provide a zero reference at the output of the receiver. The tuned amplifiers comprise IC-circuits which are tuned to the relevant channel frequencies. Each amplifier has a fast operating automatic gain control (AGC). The AGC in the 6F channel can be switched from fast to slow in order to enable an improved detection of any amplitude-modulated synchronizing pulses which may occur in the navigation system at the channel frequency 6F.

The tuned amplifiers 4, 5, 6 and 7 are each connected to the mixing means (mixers), 8, 9, 10 and 11, respeciiveiy, which are of an identical construction, such as the construction shown in the Figure for mixer 8. Said mixer comprises two balanced demodulators 8-1 and 8-2 which are each controlled by two local oscillator signals having opposite phases at the channel frequency 6F. The signals controlling demodulator 8-1 are in a 900 phase relationship to the signals controlling the demodulator 8-2.

The signals controlling the demodulators 8-1 and 8-2 are generated by a Johnson counter 8-3 which is connected to the output for the frequency 24F of a frequency synthesizer 12, which is controlled by a non-synchronized source of local oscillator signals 13. At the four outputs denoted by 00, 900, 1800 and 2700 the Johnson counter 8-3 provides four phase-shifted binary rectangular wave output signals which directly control the demodulators. The active filters 14 and 1 5 connected to the outputs of the demodulators and having a cut-off frequency of approximately 10 Hz remove the unwanted frequency components from the output signals which result from the control by rectangular-wave control signals and said filters at the same time reduce the bandwidth of the receiver in order to reduce noise at the output.

The output signals of the mixers 8, 9, 10 and, 11 are applied to the signal multiplexer 16, the output of which is connected to un analog-todigital converter 17, the output of which is connected to a programmable data processor 1 8.

Display means 19 and a keyboard 20 are connected to the processor 1 8.

Via a control bus 21 the processor controls the signal multiplexer 16, the buffer amplifier 3 and as the case may be the tuned amplifier 4. Said last control relative to the AGC is effected in the event that it must be possible to detect amplitude-modulated synchronizing pulses at the channel frequency 6F.

The processor 18 will be programmed for effecting synchronization of the receiver which can be done at the transmissions of the master station by detecting synchronizing pulses in the transmissions from the master station, which may either be amplitude-modulated pulses or 1800, phase-modulated pulses at the frequency 6F.

Once synchronization has been established then the receiver knows when it may expect multi-pulses from the different stations, as said pulses are transmitted in a fixed time format.

In principle, the receiver may operate with only one channel as all stations sequentially transmit a signal at one predetermined channel frequency, so that in principle all navigation information is completely present in one channel. The other channel frequencies may be used to obtain independent measuring results and thus to make it possible to obtain a more accurate final result by combining all measuring results.

An estimate of the position coordinates of the receiver can be entered in the processor 18 by means of the keyboard 20. The processor 18 converts the information applied to it by A/Dconverter 1 7 into output signals which represent the real position coordinates of the receiver.

Under the control of these output signals the display means 1 9 indicate the position of the receiver in longitude and lattitude.

The buffer amplifier 3 may be controlled by processor 1 8 for providing a zero-reference at the output of A/D converter 17.

Claims

1. A receiver for use in a navigation system, comprising a plurality of spaced transmitters transmitting synchronized navigation signals at at least one predetermined channel frequency and in a predetermined time sequence, the receiver comprising a source of local oscillator signals at the said predetermined channel frequency and mixing means for mixing the received navigation signals with the local oscillator signals operable for providing signals representing the quadrature components of the beat frequency signal between the received navigation signals and the local oscillator signals, characterized in that the mixing means comprise two balanced demodulators, each being controlled by two local oscillator signals having opposite phases, said signals being derived from a frequency synthesizer which is connected to a non-synchronized source of local oscillator signals, and the two signals controlling one demodulator being in a ninety degrees phase relationship to the two signals controlling the other demodulator, and that low-pass filters are connected to the outputs of the demodulators and the outputs of said filters are connected to respective inputs of a signal multiplexer the output of which is connected to an analog-todigital converter the output of which is connected to a programmable data processor for converting the information of the navigation signals into output signals representing the position coordinates of the receiver and display means for displaying the position coordinates under the control of these output signals.

2. A receiver, for use in a navigation system, substantially as herein described with reference to the accompanying drawing.