Author: Wg Cdr Rajagopal

Instrument Landing System Introduction to ILS Instrument landing system (ILS) provides horizontal and vertical guidance by its Localiser and Glide path to assist in bad weather landings Localiser of ILS operates on frequencies from 108 to 111.975 MHz in the VHF band Glide slope of ILS operates on frequencies from 329.15 to 335 MHz in UHF band Since localiser and glide path are paired with each other, selection of localiser automatically selects its glide path Distance from touch down are provided by marker beacons which are low powered NDB on…

Very High Frequency Omni-directional Radio Range Introduction to VOR VHF Radio Range (VOR) is an ICAO approved short range navigational aid that emits Radials Magnetic Bearings with a spacing of 1 degree which are called Radials VOR is free from Static and Night effect making it fit for air navigation during day and night VOR operates on the principle of Bearing by Phase Comparison between simultaneously transmitted Reference and Variable signals Airborne equipment consists of a receiver with a dipole antenna and its indications are presented in RMI as well…

Non-Directional Beacon and Automatic Direction Finder Introduction to NDB Non-Directional Beacon (NDB) is ground-based transmitter which is used for direction finding by the Automatic Direction Finder(ADF) NDB is transmits a Vertically polarised interrupted carrier wave signal in the LF or MF bands Transmission is omni-directional or equally spread in 360 degrees around the ariel Frequencies allocated to the NDB are from 190 to 1750 kHz in LF and MF bands NDB Ariels are huge ‘T’ shaped due to their high wave length Emission designators of NDB are NON-A1A or NON-A2A…

VHF Direction Finder Introduction to VDF VDF is a ground based equipment used in Air Traffic Control to find the bearing of aircrafts Bearing accuracy of VDF is up to half a degree however range information is not available VDF works in the VHF band with frequencies range between 118 to 137 MHz Loop antenna principle is used to find the direction of transmission where the transmission from an aircraft from a perpendicular direction to the loop ariel gives zero phase difference Rotating loop is replaced by electronically rotated fixed…

Antenna Transmitter and Receiver Antenna Antennas are used to transmit and receive the radio waves Antenna or Ariels should be made of good conductors like aluminium Transmitters transmit modulated wave which are demodulated in the receiver to extract intelligence Length of Antenna Ideal length of an antenna has to be proportional to the wave length Since it is difficult to construct antennas in kilometres for lower frequencies we use half or quarer wave dipole antennas Size of a Half wave dipole antenna is made equal to half the wave length…

Modulation Modulation Modulation is the process of super imposing intelligence on the carrier wave Carrier wave is capable of travelling long distances due to its high frequency and energy Amplitude and frequency of a carrier wave remains constant Signal wave is a low energy wave containing voice or data intelligence Modulation is the process of attaching the signal wave on to carrier wave for transmission Keyed Modulation Keyed modulation is the the simplest form of modulation where intelligence is sent by switching on and off the carrier wave Morse code…