- •Textbook Series
- •Contents
- •1 Properties of Radio Waves
- •Introduction
- •The Radio Navigation Syllabus
- •Electromagnetic (EM) Radiation
- •Polarization
- •Radio Waves
- •Wavelength
- •Frequency Bands
- •Phase Comparison
- •Practice Frequency (
- •Answers to Practice Frequency (
- •Questions
- •Answers
- •2 Radio Propagation Theory
- •Introduction
- •Factors Affecting Propagation
- •Propagation Paths
- •Non-ionospheric Propagation
- •Ionospheric Propagation
- •Sky Wave
- •HF Communications
- •Propagation Summary
- •Super-refraction
- •Sub-refraction
- •Questions
- •Answers
- •3 Modulation
- •Introduction
- •Keyed Modulation
- •Amplitude Modulation (AM)
- •Single Sideband (SSB)
- •Frequency Modulation (FM)
- •Phase Modulation
- •Pulse Modulation
- •Emission Designators
- •Questions
- •Answers
- •4 Antennae
- •Introduction
- •Basic Principles
- •Aerial Feeders
- •Polar Diagrams
- •Directivity
- •Radar Aerials
- •Modern Radar Antennae
- •Questions
- •Answers
- •5 Doppler Radar Systems
- •Introduction
- •The Doppler Principle
- •Airborne Doppler
- •Janus Array System
- •Doppler Operation
- •Doppler Navigation Systems
- •Questions
- •Answers
- •6 VHF Direction Finder (VDF)
- •Introduction
- •Procedures
- •Principle of Operation
- •Range of VDF
- •Factors Affecting Accuracy
- •Determination of Position
- •VDF Summary
- •Questions
- •Answers
- •7 Automatic Direction Finder (ADF)
- •Introduction
- •Non-directional Beacon (NDB)
- •Principle of Operation
- •Frequencies and Types of NDB
- •Aircraft Equipment
- •Emission Characteristics and Beat Frequency Oscillator (BFO)
- •Presentation of Information
- •Uses of the Non-directional Beacon
- •Plotting ADF Bearings
- •Track Maintenance Using the RBI
- •Homing
- •Tracking Inbound
- •Tracking Outbound
- •Drift Assessment and Regaining Inbound Track
- •Drift Assessment and Outbound Track Maintenance
- •Holding
- •Runway Instrument Approach Procedures
- •Factors Affecting ADF Accuracy
- •Factors Affecting ADF Range
- •Accuracy
- •ADF Summary
- •Questions
- •Answers
- •8 VHF Omni-directional Range (VOR)
- •Introduction
- •The Principle of Operation
- •Terminology
- •Transmission Details
- •Identification
- •Monitoring
- •Types of VOR
- •The Factors Affecting Operational Range of VOR
- •Factors Affecting VOR Beacon Accuracy
- •The Cone of Ambiguity
- •Doppler VOR (DVOR)
- •VOR Airborne Equipment
- •VOR Deviation Indicator
- •Radio Magnetic Indicator (RMI)
- •Questions
- •In-flight Procedures
- •VOR Summary
- •Questions
- •Annex A
- •Annex B
- •Annex C
- •Answers
- •Answers to Page 128
- •9 Instrument Landing System (ILS)
- •Introduction
- •ILS Components
- •ILS Frequencies
- •DME Paired with ILS Channels
- •ILS Identification
- •Marker Beacons
- •Ground Monitoring of ILS Transmissions
- •ILS Coverage
- •ILS Principle of Operation
- •ILS Presentation and Interpretation
- •ILS Categories (ICAO)
- •Errors and Accuracy
- •Factors Affecting Range and Accuracy
- •ILS Approach Chart
- •ILS Calculations
- •ILS Summary
- •Questions
- •Answers
- •10 Microwave Landing System (MLS)
- •Introduction
- •ILS Disadvantages
- •The MLS System
- •Principle of Operation
- •Airborne Equipment
- •Question
- •Answer
- •11 Radar Principles
- •Introduction
- •Types of Pulsed Radars
- •Radar Applications
- •Radar Frequencies
- •Pulse Technique
- •Theoretical Maximum Range
- •Primary Radars
- •The Range of Primary Radar
- •Radar Measurements
- •Radar Resolution
- •Moving Target Indication (MTI)
- •Radar Antennae
- •Questions
- •Answers
- •12 Ground Radar
- •Introduction
- •Area Surveillance Radars (ASR)
- •Terminal Surveillance Area Radars
- •Aerodrome Surveillance Approach Radars
- •Airport Surface Movement Radar (ASMR)
- •Questions
- •Answers
- •13 Airborne Weather Radar
- •Introduction
- •Component Parts
- •AWR Functions
- •Principle of Operation
- •Weather Depiction
- •Control Unit
- •Function Switch
- •Mapping Operation
- •Pre-flight Checks
- •Weather Operation
- •Colour AWR Controls
- •AWR Summary
- •Questions
- •Answers
- •14 Secondary Surveillance Radar (SSR)
- •Introduction
- •Advantages of SSR
- •SSR Display
- •SSR Frequencies and Transmissions
- •Modes
- •Mode C
- •SSR Operating Procedure
- •Special Codes
- •Disadvantages of SSR
- •Mode S
- •Pulses
- •Benefits of Mode S
- •Communication Protocols
- •Levels of Mode S Transponders
- •Downlink Aircraft Parameters (DAPS)
- •Future Expansion of Mode S Surveillance Services
- •SSR Summary
- •Questions
- •Answers
- •15 Distance Measuring Equipment (DME)
- •Introduction
- •Frequencies
- •Uses of DME
- •Principle of Operation
- •Twin Pulses
- •Range Search
- •Beacon Saturation
- •Station Identification
- •VOR/DME Frequency Pairing
- •DME Range Measurement for ILS
- •Range and Coverage
- •Accuracy
- •DME Summary
- •Questions
- •Answers
- •16 Area Navigation Systems (RNAV)
- •Introduction
- •Benefits of RNAV
- •Types and Levels of RNAV
- •A Simple 2D RNAV System
- •Operation of a Simple 2D RNAV System
- •Principle of Operation of a Simple 2D RNAV System
- •Limitations and Accuracy of Simple RNAV Systems
- •Level 4 RNAV Systems
- •Requirements for a 4D RNAV System
- •Control and Display Unit (CDU)
- •Climb
- •Cruise
- •Descent
- •Kalman Filtering
- •Questions
- •Appendix A
- •Answers
- •17 Electronic Flight Information System (EFIS)
- •Introduction
- •EHSI Controller
- •Full Rose VOR Mode
- •Expanded ILS Mode
- •Full Rose ILS Mode
- •Map Mode
- •Plan Mode
- •EHSI Colour Coding
- •EHSI Symbology
- •Questions
- •Appendix A
- •Answers
- •18 Global Navigation Satellite System (GNSS)
- •Introduction
- •Satellite Orbits
- •Position Reference System
- •The GPS Segments
- •The Space Segment
- •The Control Segment
- •The User Segment
- •Principle Of Operation
- •GPS Errors
- •System Accuracy
- •Integrity Monitoring
- •Differential GPS (DGPS)
- •Combined GPS and GLONASS Systems
- •Questions
- •Answers
- •19 Revision Questions
- •Questions
- •Answers
- •Specimen Examination Paper
- •Appendix A
- •Answers to Specimen Examination Paper
- •Explanation of Selected Questions
- •20 Index
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Properties of Radio Waves
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The Radio Navigation Syllabus . . . . . . . . . . . . . . . . . . . . |
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Electromagnetic (EM) Radiation |
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Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . |
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Radio Waves |
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Wavelength . . . . . . . . . . . . . . . . . . . . . . . . . . |
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Frequency Bands . . . . . . . . . . . . . . . . . . . . . . . . |
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Phase Comparison . . . . . . . . . . . . . . . . . . . . . . . . |
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Practice Frequency (f) - Wavelength (λ) Conversions |
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1 Properties of RadioWaves
Waves Radio of Properties 1
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Properties of RadioWaves 1
Introduction
Radio and radar systems are now an integral and essential part of aviation, without which the current intensity of air transport operations would be unsustainable. In the early days of aviation aircraft were flown with visual reference to the ground and flight at night, in cloud or over the sea was not possible. As the complexity of aircraft increased it became necessary to design navigational systems to permit aircraft to operate without reference to terrain features.
The early systems developed were, by modern standards very basic and inaccurate. They provided reasonable navigational accuracy for en route flight over land, but only a very limited service over the oceans, and, until about 40 years ago, flight over the oceans used the traditional seafarer’s techniques of astro-navigation, that is using sights taken on the sun, moon, stars and planets to determine position. Developments commenced in the 1910s, continued at an increasing rate during the 1930s and 1940s and up to the present day leading to the development of long range systems which by the 1970s were providing a global navigation service.
It is perhaps ironic that, having forsaken navigation by the stars, the most widely used navigation systems in the last few years are once again space based, that is the satellite navigation systems we now take as being the norm. Whilst global satellite navigation systems (GNSS) are becoming the standard in aviation and many advocate that they will replace totally all the terrestrial systems, the ICAO view is that certain terrestrial systems will have to be retained to back up GNSS both for en route navigation and runway approaches.
The development of radar in the 1930s allowed air traffic control systems to be developed providing a control service capable of identifying and monitoring aircraft such that aircraft operations can be safely carried out at a much higher intensity than would be otherwise possible. Modern satellite technology is being used to provide a similar service over oceans and land areas where the provision of normal radar systems is not possible.
The Radio Navigation Syllabus
The syllabus starts by looking at the nature of radio waves and how they travel through the atmosphere. This is essential to understand why different radio frequencies are selected for particular applications and also the limitations imposed. The introductory chapters also cover how radio waves are produced, transmitted, received and how information is added to and recovered from radio waves.
Electromagnetic (EM) Radiation
If a direct electric current (DC) is passed through a wire then a magnetic field is generated around the wire perpendicular to the current flow.
If an alternating electric current (AC) is passed through the wire then, because the direction of current flow is changing, the polarity of the magnetic field will also change, reversing polarity as the current direction reverses. At low frequencies the magnetic field will return to zero with the current, but as frequency increases the magnetic field will not have collapsed completely before the reversed field starts to establish itself and energy will start to travel outwards from the wire in the form of electromagnetic radiation i.e. radio waves.
Properties of Radio Waves 1
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1 Properties of RadioWaves
Waves Radio of Properties 1
The resulting EM energy is made up of two components, an electrical (E) field parallel to the wire and a magnetic (H) field perpendicular to the wire.
Figure 1.1 Vertical polarization
Polarization
The polarization of radio waves is defined as the plane of the electric field and is dependent on the plane of the aerial. A vertical aerial will emit radio waves with the electrical field in the vertical plane and hence produce a vertically polarized wave, and a horizontal aerial will produce a horizontally polarized wave.
To receive maximum signal strength from an incoming radio wave it is essential the receiving aerial is in the same plane as the polarization of the wave, so a vertically polarized radio wave would require a vertical aerial.
Circular polarization can be produced in a variety of ways, one of which is using a helical antenna. In circular polarization the electrical (and hence magnetic) field rotates at the frequency of the radio wave. The rotation may be right handed or left handed dependent on the orientation of the aerial array.
For reception of a circularly polarized wave an aerial of the same orientation is required, or a simple dipole aerial. There are two significant advantages. Firstly in radar systems, if circular polarization is used, when the energy is reflected from water droplets the circularity is reversed and therefore the ‘clutter’ caused by precipitation can be eliminated. Secondly, if a dipole aerial is used the orientation of the aerial is no longer critical, as it is with linear polarization, and, clearly, this will be a major advantage in mobile systems, such as cellular phones and satellite communication and navigation systems.
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