GB2150781A - Navigation system ground station - Google Patents

Abstract

The ground station of a navigation system (e.g., a VOR beacon) contains a facility (30) which detects faults during operation of the station. Data about the detected fault and/or the status of the ground station are transmitted as coded speech information superimposed on the normal transmissions at regular intervals to the normal users of the system, who then pass the information on to a central station. <IMAGE>

Description

SPECIFICATION Ground Station of a Navigation System The present invention relates to a ground station of a navigation system which contains means for detecting faults in the ground station.

A ground station of this kind is described in an article by G. Höfgen, "VOR und Doppler-VOR", Elektrisches Nachrichtenwesen, Vol. 50, No. 4, 1975, pages 259-262. This article describes only VOR and DVOR ground stations, but the invention relates to any type of ground station. Another possible ground station is the well-known NDB ground station.

If such a ground station is not too far from a maintenance centre, it can be connected to the maintenance centre by a telephone line, so that it is possible to transmit fault messages from the ground station to the maintenance centre. Fault messages can also be transmitted to the maintenance centre over a radio link specifically installed for conveying the fault information. However, these solutions are too costly if the distance to the nearest maintenance centre is very great. This is frequently the case with ground stations used for en-route navigation. Many such ground stations are located in the desert or the jungle.

The ground stations installed there are visited at regular intervals by maintenance personnel who evaluate the fault messages stored in the station.

This is very disadvantageous in that faults are not known prior to such a visit, so that the fault may not be correctible immediately because the necessary material is not available.

In addition, this procedure entails great expense.

The invention seeks to provide a solution which permits any faults to be signalled in a simple manner.

According to the invention there is provided a ground station of a navigation system which contains means for detecting faults in the ground station, wherein there is provided additional means which modulates the signal to be radiated by the ground station with the fault message and/or status messages.

With the novel solution, faults and statuses can be signalled in a simple manner even if the nearest maintenance centre is a very great distance off. In cases where fault messages would be transmitted over telephone lines or radio links, it is no longer necessary to install such equipment specificaliy for this purpose.

The signals which are radiated by the ground station are also used to transmit the messages, i.e.

no additional transmitters are required. This is of great importance especially if the power source for the station is a solar-cell array, because in such a case available electric energy is limited.

If the NDB or VOR (DVOR) ground station is near a ground station which has no voice channel, the ground station having a voice channel can also transmit fault messages of the other ground station, because it is readily possible to transmit the message from the ground station without voice channel to the ground station with voice channel.

In order that the invention and its various other preferred features may be understood more easily, an embodiment thereof will now be described, by way of example only, with reference to the drawings in which: Figure lisa block diagram of a conventional VOR ground station, and Figure 2 is a block diagram of that portion of the novel VOR ground station which is necessary for an understanding ofthe invention.

As an example of a ground station, a VOR ground station has been chosen for the followin3 description. For a better understanding of the invention, the conventional VOR ground station will be described first with the aid of Figure 1.

Atransmitter S of the VOR ground station consists of a master oscillator 8, a carrier transmitter 7, and an electronic goniometer 9. A modulator 6 provides a voltage U(mod) for modulating the carrier transmitter 7. In the modulating signal U(mod), speech, identification, and a 9,960-Hz subcarrier wave frequency-modulated with a 30-Hz reference signal are additively combined. A master switch 5 is controlled by a control logic 4. Via this switch, the modulator 6 is connected to a power supply 2. As an emergency power supply, a battery 1 is provided whose voltage is applied to the control logic 4 and the master switch 5. The signals generated by the transmitter S are fed to an antenna system 10. The antenna system 10 contains a turnstile antenna and an omnidirectional antenna.The turnstile antenna is fed from the goniometer 9 and radiates a rotating figure-8 pattern, and the omnidirectional antenna is fed from the carrier transmitter 7. The speech information is thus radiated via an omnidirectional pattern.

A dipole 11 in the radiation field receives the signal radiated by the VOR ground station and feeds it to a monitor 3. The latter monitors, inter alia, whether the radiated VOR navigation signal has the predetermined parameters, and the operation of the transmitter.

If the radiated VOR signal does not meet ICAO requirements, the control logic switches the VOR ground station off, or if the VOR ground station is an installation in which the transmitter is duplicated, over the standby transmitter.

Aside from errors which result in the installation being immediately switched off, or over, any deviations of the other monitored variabies from their required values are detected and stored. In conventional VOR ground stations, this stored information is transmitted to the maintenance centre at regular intervals over telephone lines or by radio, as mentioned in the introductory part of the specification.

The novel ground station works as follows.

In addition to the radiation-field parameters, the general status of the ground station is monitored.

This includes: condition of the electric generators, temperature in the ground station, whether ground station has been broken into. For each monitored function, an output signal (e.g. a signal with a level dependent on the result of the monitoring) is delivered. Information on events or defects that are present for a short time or one time only (short-time sharp temperature rise, break-in) is stored. Afacility compares the actual values with the required values at regular intervals (e.g. every 2 to 120 minutes) or after the occurrence of special events, and records alarm messages and other deviations from the prescribed conditions.

This information can be converted into speech signals by electronic means, and the transmitter is modulated with these speech signals. The information so radiated can be received and reproduced by commercially available airborne VOR equipment. The pilot who has received the message passes the information on to the nearest maintenance centre. It is also possible for aircraft to fly over the ground stations at regular intervals by order of the maintenance centre to receive the messages.

The messages may be transmitted in coded form so that the pilot cannot receive them in clear text. A device selects the code words from a memory according to the information to be transmitted.

Afew examples of code words and their meanings are as follows:- alfa 6: standby transmitter off alfa 5: main transmitter off bravo 1: azimuth monitor 1 signalling failure bravo 2: 30-Hz monitor 1 signalling failure charly 1: ground station broken into delta 4: fuel level too low etc.

If the pilot receives the ammouncement"V-O-R check, Alfa five, charly one, delta four", and passes this information on to the maintenance centre, it can be determined there which faults have occurred. If the VOR ground station is operating normally, the announcement "V--OO-R check passed" will be transmitted.

If the ground station fails as a result of a fault, the fault is detected and stored. After a failure of the installation, only voice messages are transmitted in a manner known per se. To this end, the final stages of the main transmitter and the standby transmitter are alternately turned on, by the monitoring facility, at regular intervals and for short times, and the last stored status of the previously operational installation is transmitted. During the short onperiods, it must be ensured that the radiated signal becomes "unflyable", because the installation has a fault which would result in false navigation if the radiated navigation signal were evaluated. The radiated navigation signal becomes "unflyable" if the reference signal is turned off.

A possible implementation of the novel ground station will now be described with the aid of Figure 2.

The master switch 5, the modulator 6, the control logic 4, the monitor 3, and the battery 1 of Figure 1 are present in Figure 2. Afacility 30, which monitors the various operational conditions and generates the signal containing the fault and status messages, is connected to the monitor 3, the control logic 4 and the modulator 6. If the transmitter is turned on to transmit message signals only, it must be insured that the radiated signal is "unflyable" as mentioned above. This is done by turning off the reference signal, as mentioned above. In the novel ground station, the reference signal is superimposed on other signals, which will be explained later. It must therefore be ensured that, when the installation is faulty, the reference signal is not superimposed on those other signals.This is done by interrupting the transfer of the reference signal by means of a switch 28 during the time that the transmitters are activated by the facility 30 via the control logic 4 to transmit the status and fault messages, i.e. while the installation is operating in the emergency mode.

In the ground station, the following signals are fed to the facility 30 (the following selection is arbitrary): the output signal of the monitor 3, designated in Figure 2 by S1; a signal S2 indicating the temperature of carrier transmitter 7; a signal S3 indicating the status of the battery 1; a signal S4 indicating the status of a generator 24 serving as a power source for the ground station; a signal S5 which indicates how much fuel is left in a tank for the generator 24; and a signal Sn provided by a device 26 and indicating whether the ground station was broken into.

In the facility 30, the signals S1 to Sn are applied to an interface 23. If further statuses are to be monitored, this interface will be fed with correspondingly more status-indicating signals.

This will be the case, for example, if the VOR ground station is colocated with other navigation facilities, such as DME and NDB, which have no voice channel of their own but whose statuses are to be monitored as well. The interface converts the levels of the signals supplied to it into levels suitable for further processing in the facility 30. In addition, it provides electric isolation between the individual sensors and the other devices within the facility 30, and converts the input signals, which are applied in parallel form, into serial data packets with the aid of a multiplexer.

These serial data packets are fed to a computer and memory 22. The memory holds the required values of the signals to be monitored. The computer samples the input signals at regular intervals of time and compares the value with the required values.

After occurrence of a special event, such as the turning off of a transmitter, the sampling instant can also be made dependent on the occurrence of this special event. Depending on the result of the comparison, the computer provides signals which either specify the respective fault or indicate that the installation is operating correctly. These signals are fed to a speech-processing circuit 21, which contains a commercially available speech processor. In this speech processor, a vocabulary of 255 words is stored. According to the input signal, a given word is selected from the memory. The velocity and pitch of the speech are adapted to the requirements for reception in the aircraft. To prevent the navigation signals from being influenced by the speech signals, a speech compressor is provided which limits the volume range of the speech signals produced in the speechprocessing circuit. The output signals of the speechprocessing circuit are applied to an adder 20. The latter is also presented with the identification, the reference signal, and the output signal of a microphone (voice channel). Over the voice channel, the adder is supplied with signals containing weather data, for example. The adder adds the signals applied to it and thus provides a signal which is the modulating signal forthe modulator 6. By a special circuit, over-modulation is avoided.

If an output signal of the monitor indicates that the ground station is faulty, changeover to the emergency mode is effected. In this mode, the status which resulted in the failure of the ground station is stored. All other messages are currently transmitted to the facility 30, sampled, compared, and then processed as previously described.

Claims (5)

1. A ground station of a navigation system which contains means for detecting faults in the ground station, wherein there is provided additional means which modulates the signal to be radiated by the ground station with the fault message and/or status messages.

2. A ground station as claimed in claim 1, wherein the message is modulated as speech upon the signal to be radiated.

3. A ground station as claimed in claim 1, wherein the message is modulated in coded form on the signal to be radiated.

4. A ground station as claimed in any one of the preceding claims, including control means whereby the messages are transmitted at regular intervals.

5. A ground station of a navigation system substantially as described herein with reference to the drawings.