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Ils vs localizer3/17/2023 ![]() ![]() The identifier is similar to the NDB and will transmit (Ident) as a sounding telegraph, the Morse code so audible with a 1020 Hz tone. The remaining 30 Hz signal is added to the subcarrier, as well like the third part, which is the identifier of the VOR. This changes the instantaneous frequency of the subcarrier 30 times per second from 9.96 kHz to 9.96 + 0.48 kHz, 9.96 kHz, 9.96-0.48 kHz and backwards to 9.96 kHz. The frequency of the subcarrier was set at 9.96 kHz, the cosinusoidal course of one of 30 Hz signals frequency modulates this with a frequency deviation of ± 480 Hz. Otherwise, the two signals will be in the coverage area of the station overlay and be cancelled. ![]() Since the searched-after line is obtained by means of a phase comparison of two signals with a frequency of 30 Hz each, one of these signals must be transmitted on a subcarrier. The signal of a VOR station settles (regardless of the above indicated technical realization of the ground station) from a total of three signal components together. The difference is M (150Hz) - M (90Hz) = 0%. This means that you receive both sound signals with 20% modulation level. You receive only the signal of the middle single dipole. The field strength is only of minor importance.Įxactly in the middle in front of the antenna line you are in the zero point of all antenna pairs. The difference is called DDM (Difference in Depth of Modulation) and is the essence of the ILS functionality. The actual information is now in the Difference of the modulation degrees of these sound signals. The two sound signals are at the LLZ, as described above, modulated with 20% modulation level. The most important parameter of an ILS signal is the degree of modulation. Subsequently, cosΨ ≈ 1 can be set, because ILS elevation is small.īy increasing the distance d is the number of maxima and minima of the resulting directional characteristic larger, this is symmetrical to the angle Θ = 0 (Landing trajectory). Where C (Θ, Ψ) is the directivity of the single dipole, the parenthesis pressure to the right of C describes the directivity of two instead of the single antenna imaginary omnidirectional antenna. The basic formula with the same shifted signal φ to calculate the electric field component E as a function of azimuth angle Ɵ and the elevation Ψ is given when the individual antennas with opposite phase currents are fed: This forms by superimposing the individual signals the required signal in space. A load distributor (Antenna Distribution Unit, ADU) divides the RF by amount and Phase to a sophisticated system on the individual antennas, each for CSB and SBO according to different laws. The basic ILS signals (COD and SBO) are fed into the up to 21 dipoles via a high-frequency load distributor that feeds the transmitting antenna. Where k is the relative level of the SBO signal relative to the CSB signal, and f is the relative phase of the SBO signal to the CSB signal, and Again, the mathematical formula:ĭ(t) = k cos(ωt + f i) (2) In this SBO signal, the 150Hz NF signal becomes out of phase and the 90Hz AF signal in-phase modulated relative to the COD signal. In addition, a signal with suppressed carrier (SBO, Side Bands Only) is generated. ![]() M90 and M150 are the modulation factors, those at which LLZ = 0.2 is to be set. Where ω caris the angular frequency of the carrier and ω fundthe angular frequency of theģ0 Hz fundamental frequency. ![]() Mathematically, it can be described as follows: This signal is called CSB (Carrier and Side Bands). The carrier oscillation in the localizer frequency range is 108.00 MHz to 111.975 MHz modulated with a 90Hz and a 150Hz tone signal. The modulation type of all ILS transmitters is the good old amplitude modulation (AM). The infographic below describes the system architecture of an Instrument Landing System.įig1. Instrument Landing System ILS ILS System Overview This article uses the following abbreviations: This article requires an advanced knowledge of mathematics. This article describes signals and operation of an Instrument Landing System ILS, Distance Measuring Equipment DME and a VHF Omnidirectional Range (VOR). ![]()
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