IE53729B1 - A receiver device for at least two radio navigation systems - Google Patents

Abstract

1. Receiver device of at least two radio-navigation systems comprising means (11, 12, 13) for the reception of the radio-navigation signal, a selector (14) having a plurality of positions, an automatic gain control circuit (2), a digital sampling circuit (3) receiving sampling control pulses, a clock (6), a microprocessor (4) receiving the sampling signals from said digital sampling circuit (3) and arranged to perform a processing of the signals and computations of positions in accordance with said radio-navigation systems, characterized in that said reception means are constituted by a plurality of reception filters (11, 12, 13) corresponding to said radio-navigation systems and switched by the selector (14), that the output of the selector (14) is connected to the sampling circuit (3) through the automatic gain control circuit (2), that a time base (5) receiving the signals of said clock (6) divides the latter in a ratio permitting a plurality of samplings during a transmission interval of the radio-navigation system comprising the longest transmission interval, to supply said digital sampling control pulses, and in that the microprocessor (4) is arranged for the sequential switching of said selector (14) and modifying the ratio of division of the time base (5) in a manner to synchronize the sampling with the other radio-navigation system so that a time multiplexing of the reception of said systems is obtained.

Description

The invention concerns a receiver device for at least two radio navigation systems.

Existing radio navigation receiver devices of this type are used to locate the position of a moving object by means of transmissions from at least two radio navigation systems. Measurements taken by at least two systems are compared in such receivers, which are expensive to build, since two separate receivers have to be combined in a single box.

This invention concerns an improvement in the structure of a receiver device of this type, reducing the cost of such an appliance.

The invention provides a receiver device for at least two radio navigation systems, which comprises a number of reception filters corresponding to the number of radio navigation systems, a multi-way selector to switch over these filters, and the output of which is connected through an automatic gain control circuit to a digital sampling circuit, also receiving sampling activation pulses, a microprocessor receiving sampling signals from the digital sampling circuit, and designed to calculate positions on the basis of the radio navigation systems, and time base receiving signals from a local clock and dividing them into a ratio permitting a plurality of samplings during a transmission interval of the radio navigation system comprising the longest transmission interval, in order to issue the sampling activation pulses, and furthermore wherein the microprocessor is designed to perform seq30 uential switching of the selector and to alter the timebase division ratio so as to synchronize the sampling with the other radio navigation system, so as to provide timewise multiplexing of radio navigation system reception.

The microprocessor may also be designed to provide sequential alteration of the amount of gain of the automatic gain control circuit.

In one embodiment of the invention, for reception of one radio navigation system with change of frequency, the device comprises a mixer, to receive the signal from a local oscillator, and the microprocessor is designed to switch the selector in such a way that the mixer also receives signals from the rece tion filter corresponding to the system to be received with change of frequency, and that a filter of another system receives the mixer output signal, the output from this filter forming the selector output. The radio navigation system to be received with change of frequency may be the LORAN system in the interference detection phase, the local oscillator being tu nable.

The device may be adapted to receive at least three radio navigation systems, in which case it comprises, for reception of a first such system with double change of frequency, two frequency mixers, each receiving a signal from a local oscillator, and the microprocessor is designed to switch the selector in such a way that the first mixer also receives the output signals from the reception filter for the first system, that a filter of the second system receives the output signals from the first mixer, that the second mixer also receives the output signals from the second system filter, that the filter of the third system receives the outDut signals from the second mixer, and that the oulnut from this third filter forms the selector ouiput. The first u 7 system may be selected from the group comprising marker beacons, radio beacons and direction finders; the second system may be LORAN, and the third OMEGA; at least the first local oscillator for the first mixer may be tunable. In one recommended embodiment, the first system may be differential OMEGA, transmitted from radio beacons or marker beacons.

In one recommended alternative embodiment, the mixer is a switch controlled by the corresponding oscillator, at least in the presence of an enabling signal representing the receiver configuration.

In another embodiment, the microprocessor is designed to accumulate programmed time intervals, and to calculate by iteration the time elapsing between the end of a samoling period for one system and the start of a sampling period for the next system, in such a way that no such time lapse is shorter than a given duration, nor exceeds this same duration plus the inverse of the frequency of sampling for either system, and that resumption of synchronization is positioned in a stationary manner.

Further details of the invention will emerge from the following description of some of the possible embodiments, with reference to the accompanying drawings : - figure 1, showing a receiver device using timewise multiplexing; - figures 2a and 2b, illustrating OMEGA and LORAN sampling patterns; - fiqure 3, illustrating control of switching between OMEGA and LORAN; - figures 4 and 5, showing recommended alternative embodiments, using at least one OMEGA filter for a frequency change involving reception of another radio navigation system; - figure 6, showing a variant on figure 4.

Figure 1 shows a combined receiver for OMEGA and LORAN C systems, comprising a filter and switching circuit 1, containing OMEGA filters 11, and a LORAN C filter 12, and a selector 14. Standard OMEGA filters comprise three individual filters Fq (10.2 KHz), Fj (11.3 KHz) and F? (13.6 KHz), which are thus tuned to the three frequencies commonly used to calculate the position of the moving object. Each of these filters can have a pass band of between - 10 and - 500 Hz. The LORAN C filter 12 has a nominal frequency of 100 KHz and a pass band of approximately * lOKHz.

When the selector 14 receives an order, it controls these filters, connecting their outputs in turn to the input of an automatic gain control, circuit 2, which acts on a digital sampling circuit 3, formed of a sampler 31 and a digital/analog converter 32.

The sampler 31 is controlled by a time base 5, which receives pulses from a local clock 6. The position of the selector 14, and the division ratio of the time base 5, are controlled by a microprocessor 4, to provide timewise multiplexing of reception of the OMEGA and LORAN C systems. The automatic gain control circuit 2 may be self-controlled, or controlled by the microprocessor 4, so that its gain corresponds to a maximum number of significant bits during digitization in the converter 32. For example, the gain control circuit 2 may be a gain amplifier programmable in steps. More specifically, the gain needed in the programmable-gain amplifier is linked at all times to the station being received, which itself is known, ,/29 through the selected input filter (reception frequency), and through synchronization of the system (station active at given time on the frequency received). For the OMEGA system, there are three frequencies and eight stations, i.e. 24 possible gains in store, and for the LORAN C system there is one frequency and five stations, i.e. 5 possible gains in store. These gain levels are determined by examining the output signal from the A/D converter 32, and increasing the gain in the amplifier 2 until a given percentage, e.g. 10%, of clipped samples is obtained in the converter 32. These individual automatic gain control circuits for each station are stabilized slowly from a mean initial level.' Consequently, the microprocessor stores the gains needed for each station, and controls the AGC circuit 2, as well as the filter to be used, and the time of sampling. This can be done by altering gains in a ratio of /2 at each change of level and with 4 bits, i.e. 16 possible gain levels, adequate to cover the reception dynamic.

The time base 5 may be a programmable time-interval generator (e.g. a MOTOROLA 6840 circuit), ensuring sampling at times laid down in the microprocessor programme.

Since the OMEGA system uses time signals in groups of 8, in 10-second formats, whereas the LORAN C system operates on a pulse basis, at a far faster rate of repetition (40 to 100 ms), 10 seconds would be a suitable time unit for multiplexing of the two systems, with synchronization on OMEGA signals, in order to correspond to eight consecutive signals, oi eferably with the same OMEGA format.

After startup, this receiver device performs the following operating 3 7 2 0 sequence. The first stage consists of obtaining synchronization on OMEGA formats. The device is used as an OMEGA receiver, with switching between filters Fq, Fj and Fg, until synchronization on OMEGA formats is obtained so as to adjust multiplexing periods to OMEGA formats. The second stage consists of obtaining synchronization for the two systems. Provided that the local clock 6 is stable enough, at least statistically, this stage can be performed with multiplex operation. Statistical accruement is obtained for a number of OMEGA formats, e.g. 5 to 10 for each system, in order to obtain positional data. During multiplexing, the microprocessor 4 stores the accumulated pulses from the local clock 6, while keeping instructions issued to the time base 5 updated, as well as data for previous samplings. Instructions given to the time base 5 involve an order to Droduce a sampling pulse after a programmable number of jump pulses from the local clock 6. The accumulation of these jump instructions is therefore representative of the accumulation of local clock pulses.

The device can then function continuously in multiplexing, i.e. alternately as an OMEGA receiver during ari OMEGA FORMAT, and as a LORAN C receiver during the next format.

Accrued clock pulses are used lo control multiplexing, and for roqain of synchronization, which is practically immediate after switching from one system to the other.

As shown in figure 2a, OMEGA processing is obtained by sampling at the three frequencies 10.2, 11.3 and 13.6 Khz, by means of pulses in pairs in quadrature, i.e. ir/2 apart (24, 22 and 18 microseconds j ΰ I .. J respectively), module Zn. Sampling frequency is a sub-multiple of the three OMEGA frequencies stated above, e.g. 188.88 Hz. If Τθ, and T2 are oeriods corresponding to frequencies Fq, F^ and Fg, and k0, K| and K2 are integers not less than 0, then during a period 1/F^ the microprocessor 4 Droduces a sequence of 3 pairs of sampling pulses with intervals of Τθ(1/4 + Κθ), T|(l/4 + K^) and T2(l/4 + K2), the first pulses in succeeding pairs preferably being 1/3^ apart. Κθ, and Kp are chosen in such a way as to distribute sampling pulses uniformly within the period (which is approximately 5.29ms in this example). Naturally, such samnlings are effective only during the useful carts of signals, lasting from 0.9 to 1.2 seconds, depending on the signals. Consequently, each OMEGA format begins and ends with a time lapse, since the effective part of the first and last signals is 0.9 and 1 second respectively.

Filters therefore merely need to be switched over between the OMEGA system and the LORAN C system every 10 seconds, and the corresponding samolina rates generated. Updating of accrued local clock pulses means that synchronization of one system is not implemented when the device is operating with the other system.

As shown in figure 2b, the LORAN C system comprises transmissions of pulse sequences from 4 local stations, one master station and three slave stations X, Y and Z, at a reception rate Τθ which may be approximately 40 to 100 ms, d>pending on groups of local stations. Tach station in turn transmits 8 nulses. Three samples are taken for each pulse, i.e. 96 samples in the course of Τ». b 3729 Figure 3 shows the sequence of four 10-second periods synchronized on OMEGA formats, for multiplexed receptions of OMEGA and LORAN C, i:e. periods corresponding to periods (N-l) and N for the LORAN C system, and to periods N and (N + 1) for the OMEGA system. Synchroni5 zation on OMEGA format gives time tj every 10 seconds. Transition between OMEGA and LORAN C samplings takes place as follows.

The exact timing of the end of the OMEGA period N is known, through accrument of intervals programmed by the microprocessor at time base level. If it is assumed that this N period is the one by which OMEGA synchronization is taken to be obtained, a time interval or lapse Atn is chosen arbitrarily, e.g. equal to 0.5 to 1.5 Τθ, and LORAN C sampling is activated from time tg at the end of this interval. As shown in figure 2b, this time tg can be positioned in any way in relation to LORAN C transmission periods. From tg on, the microprocessor estimates what will be the time tQ within period N, corresponding to the most favorable LORAN sampling, to halt such sampling. This time ίθ is on the one hand separated from time t? by an interval Κ'^Τθ where K'N is a whole number, and on the other hand from time t'p marking the start of period (N+l), corresponding to OMEGA sampling, in a time At'^, which is not less than Tg.

For LORAN sampling period (N+l), the microprocessor calculates the interval Κ^Τθ separating time ίθ in LORAN sampling period N from time tg in LORAN sampling period N+l. is a whole number, and At^ must be as small as possible, though with a lower limit, e.g. 0.5 Τθ so that the microprocessor will have time to perform the necessary switching operations. Under these circumstances, At^ will fluctuate between 0.5 and 1.5 Τθ for subsequent sampling periods, with the cycle continuing as long as the device remains in operation.

Figure 4 shows an OMEGA/LORAN C/285-425 KHz-band receiver incorp5 orating a recommended embodiment of the invention, with filters 11 and 12 shown in figure 1, and the switching circuit 14, in the form of switches Αθ, A^, A? and D, located at the outputs from filters Fq, Fp F^ and 12 respectively. This embodiment contains a more sophisticated switching circuit, including switches that allow the LORAN C filter and one OMEGA filter, e.g. F^, to be used to provide a double frequency change, for reception of direction-finder, radio-beacon or marker-beacon transmissions.

More specifically, a filter 13is combined with an aerial capable of receiving all three systems. The pass band of filter 13 extends from 285 to 425 KHz, so that it is equally suitable for direction finders and for radio and marker beacons, such as transmissions of differential OMEGA corrections. Filter 13 is connected to a mixer 15, which also receives signals from a local oscillator OLp and its output is connected to the innut of the LORAN C filter 12, through a switch G. The output from the LORAN C filter is connected, above switch D on the circuit, to a mixer 14 which also receives signals from a local oscillator 0L2, and the output of which is connected to the input to filter F2, through switch E.

The following three types of operation are made possible by multiplexing: a - OMEGA reception : switches D, G and E are open; a switch B2 above Fg is closed, and switches Αθ, A* and Ag are closed in turn, for sampling reception of the three normal OMEGA frequencies; b - LORAN C reception : switches Αθ, lp Ag and G are open; and a switch C above the LORAN C filter 12 is closed, as well as switch 0; c - 285-425 KHz-band reception : switches Αθ, Ap Bg, C and D are open, and switches Ag, E and G are closed; signals from filter 13 are fed into the LORAN C filter 12 after passing through the mixer 15, then into filter Fg after passing through mixer 14; LORAN C and Fg filters thereupon act as intermediate frequency filters for 285-425 KHz-band reception.

Detailed operation for 285-425 KHz-band reception is described below. The filter Fg has a frequency of 13.6 KHz, and if a local oscillator OLg with a fixed frequency FOg is selected, the first intermediate frequency Flp expressed in KHz, will therefore be : Flj = FOg - 13.6.

Fl^ must lie within the band pass of LORAN C filter 12. If FOg is 125 KHz, then Flj will be 111.4 KHz, which is on the edge of the LORAN C filter band. However, this keeos the image frequency of the second frequency change as far away as possible, i.e. Flj + 2Fg, i.e. 138.6 KHz.

Tuning on the 285-425 KHz band is obtained by the local oscillator OLp, in fact a synthesizer, the frequency of which ranges from 285 + FIj to 425 + FI.|, i.e. in this case 396.4 to 536.4 KHz. The image frequency of the first frequency change varies from 285 + 2FIp to 425 + 2FIp i.e. 507.8 to 647.8 KHz.

In practice, it is advisable to use a synthesizer OLj with an output frequency varying in steps of 100 or 200 Hz, and a filter F2 with a pass band of 300 Hz. These parameters are particularly suitable for both for OMEGA reception, and for reception in the 285-425 KHz band, and especially for reception of differential OMEGA transmissions ob5 tained by phase modulation of a radio or marker beacon. A synthesizer can also be used for the local oscillator OL^, to obtain fine frequency tuning.

Figure 5 shows an OMEGA and LORAN C receiver, using an OMEGA filter such as F^ to take measurements of LORAN C interference, in order to detect transmissions^ the neighbourhood of the 90-110 KHz band effective for the LORAN system, and measure their frequency. One or more suitable rejectors can then be tuned to eliminate any such interference.Transmissions likely to cause interference include frequencies 85 KHz and 112 KHz in the OECCA system.

More specifically, figure 5 shows components already included in figure 4, namely filters FQ, Fp F2 and 12, and switches Αθ, Aj , A2, B2, D and E, as well as the mixer 14 receiving signals from the local oscillator 0L?.

In order to detect interferences, the LORAN C filter 12 receives signals from the 90-110 KHz LORAN C band and side bands 70-90 KHz and 110-130 KHz, these side bands naturally being attenuated by filter 12.

Ihe local oscillator 0L2 is a variable-frequency synthesizer, such that the /0-90 KHz and 110-130 KHz side bands are brought by a frequency change to a frequency of 13.6 KHz.

For the 70-90 KHz band, the frequency F02 of the local oscillator 0L2 can range from 70 - 13.6 to 90 - 13.6 KHz, i.e. 57.4 to 77.4 KHz, with an immage frequency equal to F02 - 13.6, i.e. 43.8 to 63.8 KHz.

For the 110-130 KHz band, the frequency F02 of the synthesizer 0L2 can range from 110 + 13.6 to 130 + 13.6 KHz, i.e. 123.6 to 143.6 KHz, with an image frequency equal to F02 + 13.6, i.e. 137.2 to 157.2 KHz.

In a recommended embodiment, the frequency of the synthesizer 0l_2 varies in steps of 200 or 500 Hz, with one or more rejectors, with a 1 KHz nass band. Fiaure 5 shows two such rejectors REJj and RFJg, which can be tuned by a variable condenser (alternatively, a variable-capacity diode, the voltage of which is controlled by the microprocessor), and which can each be tuned to a transmission received on a side band.

Figure 6 shows an alternative embodiment of the device illustrated in figure 4. Switches E and G are used as mixers. To this effect, oscillators OLj and 0L2 receive the output signal from AND gates 41 and 42.

· One of the inputs to each of these AND gates 41 and 42 receives a signal S representing the receiver configuration, i.e. a logic 1 when multiplexing brinqs in reception in the 285-425 KHz band. The other input to the AND gates 41 and 42 receives signals from the corresponding local clock, i.e. OLj and 0l_2 respectively, suitably shaned, namely switching from O to 1 ?0 at the required frequency. This gives a frequency change with minimum components. When the receiver device is in the OMEGA or LORAN C reception configuration, the signal S is a logic 0, and consequently the outputs from ANO gates 41 and 42. Switches E and G are then open.

Claims (11)

1. CLAIMS;

1. A receiver device for at least two radio navigation systems, which comprises a number of reception filters corresponding to the number of radio navigation systems, a multi-way selector to switch over these filters, and the output of which is connected through an automatic gain control circuit to a digital sampling circuit, also receiving sampling activation pulses, a microprocessor receiving sampling signals from the digital sampling circuit, and designed to calculate positions on the basis of the radio navigation systems, and time base receiving signals from a local clock, and dividing them into a ratio permitting a plurality of samplings during a transmission interval of the radio navigation system comprising the longest transmission interval, in order to issue the sampling activation pulses, and furthermore wherein the microprocessor is designed to perform sequential switching of the selector and to alter the time-base division ratio so as to synchronize the sampling with the other radio navigation system, so as to provide timewise multiplexing of radio navigation system reception.

2. A device as claimed in claim 1, wherein the microprocessor is designed to provide sequential alteration of the amount of gain of the automatic gain control circuit.

3. A device as claimed in either of claims 1 or 2, wherein, for reception of one radio navigation system with change of frequency, the device comprises a mixer, to receive the signal from a local oscillator, and the microprocessor is designed to switch the selector in such a way that the mixer also receives signals from the reception filter for the system to be received with frequency change, and that a filter for another system receives the mixer output signal, the output from this filter forming the selector output.

4. A device as claimed in any one of claims 1 to 3, wherein the receiver is adapted to receive at least three radio navigation systems, and comprises, for reception of a first such system with double change of 3 3 7 2 9 frequency, two frequency mixers, each receiving a signal from a local oscillator, and the microprocessor is designed to switch the selector in such a way that the first mixer also receives the output signals from the reception filter for the first system, that a filter for the second system receives the output signals from the first mixer, that the second mixer also receives the output signals from the second system filter, that the third system filter receives the output signals from the second mixer, and that the output from this third filter forms the selector output,

5. A device as claimed in claim 4, wherein the first system is selected from the group comprising marker beacons, radio beacons and direction-finder transmitters, the second system is the LORAN longrange navigation system, the third system is the OMEGA system, and at least the first local oscillator corresponding to the first mixer is tunable.

6. A device as claimed in claim 5, wherein the first system is the differential OMEGA system transmitted from radio beacons or marker beacons;

7. A device as claimed in claim 3, wherein the radio navigation system to he received with change of frequency is the LORAN system in the interference-detection phase, and the local oscillator is tunable. R. A device as claimed in any one of claims 3 to 7, wherein one local oscillator is a synthesizer. A. A device as claimed in any one of claims 3 to 8, wherein one mixer is a switch controlled by the corresponding local oscillator, at least in the piesence of an enabling signal representing the receiver configuration.

8. 10. A device as claimed in claim 9, wherein the switch receives the output signal from an AND gate, one input of which receives the corresponding local oscillator signal, the other input receiving the logic enabling signal. 5

9. 11. A device as claimed in any one of claims 1 to 10, wherein the microprocessor is designed to accumulate programmed time intervals, and to calculate by iteration the time elapsing between the end of one sampling period for one system and the start of a sampling oeriod for the next system, in such a way that no such time lapse is 10 shorter than a given duration, nor exceeds this same duration plus the inverse of the frequency of sampling for either system, and that resumption of synchronization is positioned in a stationary manner.

10. 12. n device as claimed in claim 1, substantially as hereinbefore described with reference to ana as illustrated

11. 15 in the accompanying drawings.