NO159965B - RECEIVER DEVICE FOR AT LEAST TWO RADIO NAVIGATION SYSTEMS. - Google Patents

Description

The invention relates to a receiver device for at least two radio navigation systems of the type specified in the introductory part of patent claim 1.

Existing radio navigation systems of this type are used to determine the position of a moving object using transmissions from at least two radio navigation systems. Measurements taken by at least two systems are compared

net in such receivers, which are expensive to construct,

as two separate receivers must be combined in a single house.

From US-A-3936763 there is known a receiver device for a radio navigation system with at least two frequencies, i.e. for example an OMEGA system without modification of the signal's phase (modulus 2 77").

The present invention relates to an improvement in the construction of a receiver device of the aforementioned type, so that the price of the device is reduced.

The invention thus relates to a receiver device for

at least two radio navigation systems, of the type specified at the outset, which are distinguished by the features specified in the characterizing part of patent claim 1.

The present device is thus a receiver for at least two radio navigation systems, which includes, among other things, a multi-way selector for switching a number of receiver filters corresponding to the number of radio navigation systems, which differs from the known technique. The microprocessor may also be designed to provide sequential change of gain level-

one of the automatic gain control circuit.

In an embodiment of the invention for receiving a radio navigation system with frequency change, the device comprises a mixer for receiving the signal from a local oscillator, and the microprocessor is designed to connect the selector in such a way that the mixer also receives signals from the receiver filter corresponding to that system which is to be received when the frequency changes, and that a filter for another system receives the mixer's output signal, where the output from this filter forms the selector output. The radio navigation system to be received when the frequency changes can be the LORAN system in the interference detection phase, where the local oscillator is tunable.

The device can be adapted to receive at least three radio navigation systems. In this case, for receiving a first such system with double frequency change, it will comprise two frequency mixers, each of which receives a signal from a local oscillator, and the microprocessor is designed to connect the selector in such a way that the first mixer also receives output signals from the receiver 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 filter for the third system receives the output signals from other mixers and that the output from this third filter forms the selector output. The first system can be selected from the group comprising marker beacons, radio beacons, radio 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 a recommended design example, the first system can be a differential OMEGA, sent from a radio beacon or marker beacon.

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

In another exemplary embodiment, the microprocessor is designed to accumulate programmed time intervals and, by repetition, calculate the time that elapses between the end of a sampling period for one system and the start of a sampling period for the next system in such a way that no such time period is shorter than a given duration and also does not exceed the same duration plus the inverse value of the sampling frequency for one or the other system, and that the resumption of synchronization is set in a stationary manner.

Further details of the invention will be apparent from the following description of some possible examples with reference to the drawing, where

fig. 1 shows a receiver device that uses occasional multiplexing,

figures 2a and 2b illustrate OMEGA and LORAN sampling patterns,

fig. 3 illustrates switching management between OMEGA and LORAN,

figures 4 and 5 show recommended alternative embodiments, which use at least one OMEGA filter for a frequency change including reception of another radio navigation system,

fig. 6 shows a variant of fig. 4.

Fig. 1 shows a combined receiver for OMEGA and LORAN C systems, which comprises a filter and switching circuit 1 containing OMEGA filters 11 and a LORAN C filter 12, as well as a selector 14. Standard OMEGA filters comprise three separate filters Fq (10, 2 khz), F1 (11.3 khz) and F (13.6 khz), as thus

is tuned to three frequencies that are generally used for calculating the position of the moving object. Each of these filters can have a passband of between - 10 and - 500 hz. LORAN

The C filter 12 has a nominal frequency of 100 kHz and a passband of approx. - 10 khz. When the selector receives an order, it controls these filters and connects their outputs in turn to the input of an automatic gain control circuit 2, which acts on a digital sampling circuit 3, formed by a sampler 31 and a digital/analog converter 32.

The sampler 31 is controlled by a time base circuit 5, which receives pulses from a local clock 6. The selector 14's position and division ratio of the time base 5 is controlled by a microprocessor 4 to create periodic multiplexing of the reception of the OMEGA and LORAN C system elements. The automatic gain control circuit 2 can 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. The gain control circuit 2 can e.g. be a step-programmable gain seeker. More precisely, the necessary gain in the programmable volume control is at all times linked to the station being received, which is known in and of itself, via the selected input filter (receive frequency) and via synchronization of the system (station active at a given time on the received frequency). For the OMEGA system there are three frequencies and eight stations, i.e. 24 possible amplifications in stock, for the LORAN C system there is one frequency and five stations, i.e. 5 possible amplifications in stock. The gain levels are determined by examining the output signal from the A/D converter 32, and increasing the gain in the amplifier 2 up to a given percentage, e.g. 10%, off

limited samples are available in the converter 32. These individual automatic gain increase circuits for each station are slowly stabilized from a medium output level. Accordingly, the microprocessor will store the necessary gains for each station and control the gain circuit 2, as well as the filter to be used and the sampling time. This can be done by changing the gains in a ratio of J ~ 2 at each level change and with 4 bits, i.e. 16 possible gain levels, which are adequate for covering the reception dynamics.

Time base 5 may be a programmable time-interval generator (e.g. a MOTOROLA 6840 circuit), which ensures sampling at times fixed in the microprocessor program.

As the OMEGA system uses time signals in groups of 8,

in 10-second format, while the LORAN C system is operated on a pulse basis at a much higher repetition rate (40 - 100 ms), 10 seconds will be an appropriate time unit for multi-

plexing of the two systems, with synchronization on the OMEGA signals, to correspond to eight consecutive signals, preferably with the same OMEGA format.

After starting up, this receiving device performs the following operating sequence. The first step consists of achieving synchronization on OMEGA formats. The device is used as an OMEGA receiver, with switching between the filters F^, F^ and F^, until synchronization on OMEGA formats is achieved for setting the multiplexing periods on OMEGA formats. The second step consists of achieving synchronization for the two systems. Provided that the local clock 6 is stable enough, at least statistically, this step can be carried out with multiplex operation. Statistical collection is achieved for a number of OMEGA formats, e.g. 5-10 for each system, for obtaining position data. During multiplexing, the microprocessor 4 stores the accumulated pulses from the local clock 6, while keeping transmitted instructions to the time base 5, as well as data for previous samples up to date. Instructions given to time base 5 include an order to generate a sampling pulse after a programmable number of jump pulses from the local clock 6. The accumulation of these jump orders is therefore representative of the accumulation of local clock pulses. The device can then function continuously with multiplexing, i.e. alternately as an OMEGA receiver under an OMEGA format and as a LORAN C receiver under the next format.

Collected clock pulses are used to control multiplexing and to restore synchronization, which happens practically immediately after switching from one system to the other.

As shown in fig. 2a, OMEGA processing is achieved by sampling at the three frequencies 10.2, 11.3 and 13.6 khz, using pulses in pairs in quadrature, i.e. n/2 apart (24, 22 and 18 micro-seconds respectively), module 211 The sampling frequency FE is a factor of the three OMEGA frequencies mentioned above, e.g. 188.88 hz. If Tq, T-^ and T2 are periods corresponding to the frequencies Fq , F-^ and F 2> and Kq, K-^ and K2 are integers not less than 0, the microprocessor 4 during the period 1/F^ produce a series of 3 pairs of sampling pulses at intervals of TQ(l/4 + K0) , T-j^d/4 + K-^ and <T>2(l/4 + K2) , where the first pulses in successive pairs are preferably 1/3FE apart. Kq, and K2 are chosen in such a way that the sampling pulses are evenly distributed in the period T_ XL (which is approx. 5.29 ms in this example). Such samples are of course only effective during the useful signal portions which last from 0.9 to 1.2 seconds, depending on the signals. Consequently, each OMEGA format begins and ends with a time course, as the effective part of the first and last signal is 0.9 and 1 second respectively.

The filters must therefore only be switched between the OMEGA system and the LORAN C system every 10 seconds and the corresponding sampling rates must be generated. Updating aggregated clock pulses means that the synchronization of one system is not completed when the device is working with the other system.

As shown in fig. 2b, the LORAN C system comprises transmissions of pulse trains from 4 local stations, a main station and three controlled stations X, Y and Z at a reception speed TQ which can be approx. 40 to 100 ms, depending on the groups of local stations. Each station in turn sends 8 pulses. Three samples are taken for each pulse, i.e. 9 6 samples during T^,.

Fig. 3 shows the sequence of four 10-second periods synchronized on OMEGA formats, for multiplex reception of OMEGA and LORAN C, i.e. periods corresponding to periods (N-1) and N for the LORAN C system and periods N and (N+ l) for the OMEGA system. The synchronization in the OMEGA format gives the time t^ every 10 seconds. The transition between OMEGA and LORAN C sampling takes place in the following way.

The exact time of the end of the OMEGA period N is known through the collection of intervals, programmed by the microprocessor at the time base level. If it is assumed that this N period is the one by means of which the OMEGA synchronization is achieved, a time interval or sequence AtR is randomly selected, e.g. equal to 0.5 to 1>5 TQ, and LORAN C sampling is activated from the time at the end of this interval. As shown in fig. 2b, this time t2 can be set in an optional way in relation to LORAN C transmission periods. From t 2 onwards, the microprocessor estimates what will be the time in period N, corresponding to the most advantageous LORAN sampling, to stop such sampling. This time tg is partly separated from time t2 by an interval K'NTG, where K N is an integer, and partly from time t'^, which marks the start of the period (N+1), which corresponds to OMEGA sampling, with a time At'^, which is not less than T^,.

For the LORAN sampling period (N+l), the microprocessor calculates the interval K.,,,T„ which separates time tn in the LORAN sample

PJ+ J.G U

the sampling period N from time t2 in the LORAN sampling period N+l. KN+1 is a whole number and AtN must be as small as possible, albeit with a lower limit, e.g. 0.5 TQ, so that the microprocessor has time to carry out the necessary switching. Under these circumstances, the AtN will fluctuate between 0.5 and 1.5 TG for subsequent sampling periods, with the cycle continuing as long as the device is in operation.

Fig. 4 shows an OMEGA/LORAN C/285 - 425 khz band receiver comprising a recommended embodiment of the invention, with filters 11 and 12 as shown in fig. 1 and the switching circuit 14, in the form of switches A^, A-^, A2 and D, arranged respectively at the output of filters F^, F^, F2 and 12. This embodiment contains a more sophisticated switching circuit which includes switches that allow the LORAN C filter and an OMEGA filter, e.g. F2 is used to create a double frequency change for receiving radio direction-finding beacon or marker beacon transmissions._

More precisely, a filter 1 is combined with an antenna capable of receiving all three systems. The filter's 13 passbands extend from 285 to 425 khz, so that it is as suitable for radio direction finding devices as for radio and marker beacons, such as transmissions of various OMEGA corrections. The filter 13 is connected to a mixer 15, which also receives signals from a local oscillator OL^, and its output is connected to the input of the LORAN C filter 12 via a switch G. The output of the LORAN C filter is above switch D in the circuit connected to a mixer 14', which also receives signals from a local oscillator 0L2, the output of which is connected to the input of the filter F2 via a 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 F2 is closed and switches Ag, A^ and A2 are closed in turn for sampling reception of the three normal OMEGA frequencies;

b - LORAN C reception: switches Ag, 1^, A2 and G are open; a switch C above the LORAN C filter 12 is closed, as well

the switch D;

c - 285 - 425 khz band reception: switches Aq , A-^, B2, C and D are open and switches A2, E and G are closed; signals from filter 13 are fed into LORAN C filter 12 after passing through mixer 15, then to filter F2 after passing through mixer 14; The LORAN C and F2 filters then act as intermediate frequency filters for 28 5-4 25 khz band reception.

The detailed operation for 285-425 khz band reception is discussed below. The filter F2 has a frequency of 13.6 kHz, and if a local oscillator 0L2 with a fixed frequency F02 is selected, the first intermediate frequency FI-j_' expressed in kHz will thus become: FI1 = F02 - 13.6.

FI^ must lie within the passband of the LORAN C filter 12. If F02 is 125 khz, FI-^ will be 111.4 khz, which is at the edge of the LORAN C filter band. But this keeps the partial frequency of the second frequency change as far away as possible, i.e. Fl + 2F2, i.e. 138.6 khz.

Tuning in the 285-425 khz band is achieved using the local oscillator 01^; in reality a synthesizer with a frequency that goes from 285 + FI^ to 425 + FI]_/ ie in the present case 396.4 to 536.4 khz. The mirror frequency of the first frequency change varies from 285 + 2FI1 to 425 + 2FI1, ie 507.8 to 647.8 khz.

In practice, it is advisable to use a synthesizer oi^ with an output frequency varying in steps of 100 or 200 hz and a filter F^ with a passband of 300 hz. These parameters are particularly appropriate both for OMEGA reception and for reception in the 285-425 khz band, and especially for reception of differential OMEGA transmissions which are obtained by phase modulation of a radio or marker beacon. A synthesizer can also be used as local oscillator 0L2 to achieve fine frequency tuning.

Fig. 5 shows an OMEGA and LORAN C receiver that uses an OMEGA filter as F2 to take measurements of LORAN C interference, to record transmissions near the 90-110 khz band effectively for the LORAN system and measure their frequency. One or more appropriate blocking circuits can then be matched to eliminate any such interference. Transmissions that are likely to cause interference include 85 khz and 112 khz in the DECCA system.

More precisely, fig. 5 components which are already included in fig. 4, i.e. the filters FQ, F^ F2 and 12, the switches AQ, A^ A2, B2, D and E, as well as the mixer 14 which receives signals from the local oscillator 0L2.

To record interference, the LORAN C filter 12 receives signals from the 90-110 khz LORAN C band and the sidebands 70-90 khz and 110-130 khz, where these sidebands are of course attenuated by the filter 12. The local oscillator OL2 is a frequency-variable synthesizer, so that the 70-90 khz and 110-130 khz sidebands are brought to a frequency of 13.6 khz by a frequency change.

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 a mirror frequency equal to F02 - 13.6 i.e. 43.8 to 63.8 khz.

For the 110-113 khz band, the frequency F02 of the synthesizer OL2 can

range from 110 +13.6 to 130 + 13.6 khz, i.e. 123.6 to 143.6 khz, with a mirror frequency equal to F02 + 13.6, i.e. 137.2 to 157.2 khz.

In a recommended embodiment, the synthesizer's OL2 frequency varies in steps of 200 or 500 hz, with one or more blocking circuits with a 1 khz band. Fig. 1 shows two such blocking circuits REJ-^ and REJ2, which can be tuned with a variable capacitor (alternatively with a diode of variable capacitance and whose voltage is controlled by the microprocessor), and each of which can be tuned to a transmission received on a side band.

Fig. 6 shows an alternative embodiment of the device shown in fig. 4. Switches E and G are used as mixers. To this end, oscillators OL^ and OL2 receive the output signal from AND gates 41 and 42. One of the inputs to each AND gate 41 and 42 receives a signal S, which represents the receiver design, ie a logic 1 when multiplexing brings in reception in 285-425 khz band. The other input to the AND gates 41 and 42 receives signals from the corresponding local clock, i.e. OL^ or 0L2 in appropriate form, i.e. switching from 0 to 1 at the required frequency. This provides a frequency change with a minimum of components. When the receiver device is in OMEGA or LORAN C receiver design, the signal S is a logical 0, which the outputs from the AND gates 41 and 4 2 consequently also are. The switches E and G are then open.

Claims (11)

1. Receiver device for at least two radio navigation systems, comprising means (11, 12, 13) for receiving the radio navigation signal, a selector (14) with a plurality of positions, a control circuit (2) with automatic amplification, a digital sampling circuit (3) which receives sampling control pulses, a clock (6), a microprocessor (4) which receives the sampling signals from the digital sampling circuit (3) and is arranged to carry out a processing of the signals and calculations of positions in according to the radio navigation systems, characterized in that the receiver organs are made up of a plurality of receiver filters (11, 12, 13) which corresponds to said radio navigation systems and is switched by means of the selector (14), that the output of the selector (14) is connected to the sampling circuit (3) via the control circuit (2) with automatic amplification, that a time base circuit (5) which receives the signals from the clock (6), divides the latter in a ratio that allows a plurality of samples during a transmission interval of the radio navigation system comprising the longest transmission interval, for providing said digital sampling control pulses, and that the microprocessor (4) is arranged for sequential switching of said selector (14) and modification of the division ratio of the time base circuit (5) in order to synchronize the sampling with the other radio navigation system, so that a time multiplexing of the reception of said systems is achieved. 2. Device as stated in claim 1, characterized in that the microprocessor (.4) is designed to provide sequence change of the automatic gain control circuit's (2) gain level. 3. Device as specified in one of claims 1 or 2, characterized in that the device for receiving a radio navigation system with frequency change comprises a mixer (14') to receive the signal from a local os cillator (01^), and that the microprocessor (4) is designed to connect the selector (14) in such a way that the mixer (14) also receives signals from the reception filter for the system to be received with frequency change, and that a filter for a other system receives the mixer's (140 out) signal, where the output from this filter forms the selector output. 4. Device as specified in one of claims 1-3, characterized in that the receiver is adapted to receive at least three radio navigation systems and for receiving a first such system with double frequency change comprises two frequency mixers (14', 15), each of which receives a signal from a local oscillator (OL^, OL^), and that the microprocessor (4) is designed to connect the selector in such a way that the first mixer (15) also receives the output signals from the reception filter for the first system, that a filter for the second system receives the output signal from the first mixer (15), that the second mixer (14') also receives the output signals from the filter for the second system, that a third system filter receives the output signals from the second mixer (14<1>) and that the output from this third filter forms the output from the selector (14). 5. Device as specified in claim 4, characterized in that the first system is selected from the group that includes marker beacons, radio beacons and bearing station transmitters, that the second system is the long-range LORAN navigation system, the third system is the OMEGA system and that at least the first local oscillator (OL^) corresponding to first mixer (15) is tunable. 6. Device as specified in claim 15, characterized in that the first system is the differential OMEGA system, sent from a radio beacon or marker beacon. 7. Device as specified in claim 3, characterized in that the radio navigation system to be received with frequency change is the LORAN system in the interference-registration phase and that the local oscillator (OL2) is tunable. 8. Device as specified in one of claims 3-7, characterized in that a local oscillator (0L^,0L2) is a synthesizer. 9. Device as stated in one of claims 3-8, characterized in that a mixer (14<*>,15) is a switch (E,G), controlled by corresponding local oscillators (OL-^, OL2) at least in the presence of an opening signal (S) representing the receiver's configuration. 10. Device as stated in claim 9, characterized in that the switch (E,G) receives the output signal from an AND gate (41,42), one input of which receives a corresponding local oscillator (OL^, OL2) signal, while the second input receives the logical opening signal (S). 11. Device as stated in one of claims 1-10, characterized in that the microprocessor (4) is designed to accumulate programmed time intervals and repeatedly calculate the dead times (At^, At< tø) between the end of a sampling period for one system and the start on a sampling period for the next system, in such a way that no such dead time course is shorter than a given duration nor exceeds the same duration plus the inverse value of the sampling frequency of one of the systems, and that the resumption of synchronization is placed in a stationary manner.