Abstract: The invention deals with a surveillance system for terrestrial navigational and landing systems, in which the navigational signals being transmitted for aeroplanes or other airborne objects by the navigational and airport landing systems are received and evaluated by a ground-based receiving and control facility. In this system: the receiving and control facility is equipped with a plurality of additional receiving stations; these additional receiving stations operate in the frequency range of the navigational signals; the additional receiving stations are arranged geographically distributed within the transmitting range of the navigational or airport landing system; the signals recorded by the additional receiving stations are forwarded to a central evaluating unit.

Abstract: A method for monitoring a localizer course facility in an instrument landing system, including modulating a course signal at a first signal frequency and at a second signal frequency, and transmitting the modulated course and clearance signals. The method also includes detecting by sensors the modulated course and clearance signals, demodulating the modulated course and clearance signals, monitoring variables obtained from the demodulated course and clearance signals to ensure that the variables are within limit values, and subjecting the demodulated course and clearance signals to Fourier transformation. Also included is determining a first phase difference for a first modulation frequency between the course and clearance signals detected by the sensors and a second phase difference for a second modulation frequency in the course and clearance signals, betweem the course and clearance signals detected by the sensors.

Abstract: A glide path transmitter for an instrument landing system. The transmitter includes several antenna radiators by way of which high frequency signals containing various low frequency modulated carrier and side band components are radiated. The components overlap each other in the far field where they form a guide signal which can be evaluated by aircraft. Phases of the carrier oscillations of the radiated high frequency signals form the guide signal having a set relationship with each other. A separate digitally controlled modulator is provided for each high frequency signal fed to an antenna radiator. The modulator modulates the phase and amplitude of a high frequency oscillation fed thereto according to a given model and inputs the modulated high frequency signal into the antenna radiator allocated thereto, thus reducing the supply network expenditure.

Abstract: In contrast with conventional transmitting stations for a position locating system in which the main equipment and the standby equipment operate alternately and are monitored by checking the transmitted signal received from external sensors, the present invention monitors at least the standby equipment during inactive periods during which no signal is being transmitted. In a preferred embodiment, external sensors (FS, MF) are provided for monitoring both the main transmitter (TXM) and the main timing and control section TCS1) during transmission periods, a dummy load (DL) and an internal sensor (IS) is used for monitoring the standby transmitter (TXR) during non-transmission periods, internal monitoring information (MI) is used for monitoring the reserve timing and control section (TCS2) and the electronic antenna (EA), and the two monitor sections (MS1, MS2) contained in the monitor unit are used to monitor each other.

Abstract: Microwave landing systems are used to enable aircraft to make landings even in poor visibility. One distinguishes three categories of approach and landing manoeuvers. Of particular importance are Category III operations, i.e., those in which the pilot depends exclusively on the navigation system, because he cannot see the runway. Throughout a Category III landing operation, it must be ensured that the navigation system does not fail, and that the information contained in the signals being radiated by the navigation system is reliable. To that end, two executive monitors are arranged such that the first to detect a signal error functions as a master monitor. If the slave monitor then detects (within a reduced error threshold) the same signal error, an error in the system being monitored is confirmed and appropriate safety measures are taken (e.g. immediate changeover from the faulty transmitter).

Abstract: A transmitting station for a navigation system with dual transmitters (20A, B) is disclosed in which the dummy load, which commonly trerminates the active-standby transmitter instead of the antenna system, and the associated high-performance changeover switch are omitted. Instead, the two transmitters are operated in constant alternation. This permits better monitoring with less costly and complicated equipment.

Abstract: A system for monitoring the level of an RF signal having such a small amplitude that it must be amplified before it can be monitored. To determine the deviation of the amplifier gain from the desired value, an additional RF signal of relatively high amplitude is used and is attenuated by a predetermined amount before being applied to the amplifier. The levels of the attenuated and subsequently amplified RF signal are compared with the level of the unchanged signal. From the deviation of this ratio, the gain variation is determined.Alternatively, in lieu of gain control of the amplifier the gain variation may be mathematically offset in the digital instrumentation provided.The monitoring system is suitable for use in the so-called instrument-landing system (ILS) and in VOR and DVOR en-route navigation systems.

Abstract: In navigation transmitters it is important that the phase difference between the carrier waves of a carrier signal and the carrier waves of sideband signals be held at a constant value. To accomplish this, the carrier waves are maintained constant relative to a reference signal in a known manner. A phase meter measures the phase difference between the carrier waves of the sideband signals and the reference signal and between the carrier waves of the carrier signal and the reference signal. The measure values are used to determine the phase difference between the carrier signal and sideband signals which are compared with a desired value. Depending on the deviation from the desired value, a controllable phase shifter controls the phase of the carrier waves of the sideband signals. Since the measurements are made on a time-division multiplex basis, little circuitry is required. Any measuring errors do not affect the formation of the desired phase difference.

Abstract: A novel DME transponder having a plurality of directional antennas arranged equidistantly on a circle each having a radial, highly directional pattern and as a group covering 360.degree. in the azimuth plane. The antennas are divided into at least two groups of nonadjacent antennas. Each group is connected to a receiver. The DME reply signal is radiated from the group containing the antenna which has received the DME interrogation signal with the greatest amplitude. The signal radiated in the direction of the interrogator is the DME reply signal, and the signals radiated in the other directions are used as filler pulses.