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RADIO NAVIGATION ROBERT JURCA
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RADIO NAVIGATION ATPL Exam preparation 3
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Basic Radio Principles • VHF Direction Finding • NDB and ADF • VOR and Doppler VOR • Distance Measuring Equipment • Instrument Landing System • Marker Beacons • Microwave Landing System • Radar Principles • Ground Radar • Hyperbolic Navigation
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Table of Contents
BASIC RADIO PRINCIPLES....................................................................................3 GROUND DIRECTION FINDING (VDF)............................................................. 8 NDB AND ADF........................................................................................................10 VOR AND DOPPLER VOR................................................................................... 14 DISTANCE MEASURING EQUIPMENT............................................................21 INSTRUMENT LANDING SYSTEM...................................................................26 MARKER BEACONS.............................................................................................. 34 MICROWAVE LANDING SYSTEM.....................................................................35 RADAR PRINCIPLES.............................................................................................38 GROUND RADAR................................................................................................... 41 SECONDARY SURVEILLANCE RADAR.......................................................... 43 AIRBORNE WEATHER RADAR..........................................................................45 HYPERBOLIC NAVIGATION...............................................................................48 LORAN C..................................................................................................................49 GLOBAL NAVIGATION SATELLITE SYSTEMS (GNSS )..............................50 AREA NAVIGATION SYSTEMS..........................................................................56 INTEGRATED INSTRUMENT SYSTEM & ELECTRONIC FLIGHT INSTRUMENT SYSTEM.......................................................................................59 FLIGHT MANAGEMENT SYSTEMS (FMS)......................................................70
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BASIC RADIO PROPAGATION THEORY FREQUENCY, WAVELENGTH, SPEED OF LIGHT RELATIONSHIP 1 cycle
DEFINITIONS
Wavelength
Field strength
Amplitude
Time 0o
90o 180o
270o 360o 90o
180o
Cycle, wavelength and amplitude
Cycle
A complete series of values of a periodical process
Hertz
One Hertz is one cycle per second
Frequency
The number of cycles occurring in one second in a radio wave expressed in Hertz (Hz)
Wavelength
The physical distance travelled by a radio wave during one cycle of transmission
Amplitude
The maximum deflection in an oscillation or wave
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RELATIONSHIP
C=fλ
Where: C is the speed of Light, 300 X 106 metres per second (162 000 NM per second) f is the frequency in Hertz λ is the wavelength in metres
EXAMPLE
Prefix
Magnitude
Kilo
103 6
1000
Mega
10
1 000 000
Giga
109
1 000 000 000
-3
Milli
10
0.001
Micro
10-6
0.000001
Nano
10-9
0.000000001
What is the wavelength of an NDB transmitting on 375 KHz?
ANSWER:
C=fλ λ = C/f = 300 000 000 ÷ 375 000 = Wavelength = 800 m
FREQUENCY SPECTRUM Band
Abbreviation
Frequency
Very Low Frequency
VLF
3 – 30 Hz
Equipment
Low Frequency
LF
30 – 300 Hz
NDB Loran C
Medium Frequency
MF
300 – 3000 Hz
NDB
High Frequency
HF
3 – 30 MHz
Long range communications
Very High Frequency
VHF
30 – 300 MHz
Communications VOR ILS Localiser Marker Beacons
Ultra High Frequency
UHF
300 – 3000 MHz
ILS glidepath DME SSR SATNAV SATCOM
Super High Frequency
SHF
3 – 30 GHz
Radar Radio Altimeter
Extremely High Frequency
EHF
30 – 300 GHz
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WAVELENGTH Hectometric/Kilometric
Metric
Decimetric
Centimetric
ADF
Marker Beacon VOR ILS VDF
DME Radio Altimeter
AWR MLS SSR
Line of Sight Formula
The maximum range for VHF and UHF can be approximated by the following formula: R = 1.23√HT + 1.23√HR Where: R Range in nautical miles HT Height of the transmitter in feet HR Height of the receiver in feet
EXAMPLE
In ISA conditions, what is the maximum theoretical range at which an aircraft at FL80 can expect to obtain bearings from a ground VDF facility sited 325 ft above MSL ?
ANSWER:
R = 1.23√8000 + 1.23√325 = 110 + 22 Range = 132 NM
A and B signal received
only A signal received
only B signal received neither A nor B signal received
VOR station A
VOR station B
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CLASSIFICATION OF EMISSIONS Radio regulatory agencies have designed a coding system that fully describes the form that a radio transmission may take. The table below details the coding system.
First Character Type of Modulation
Second Character Nature of the Modulating Signal
Third Character Type of Information Being Transmitted
N
Unmodulated carrier
F
Frequency
A
Amplitude
P
Unmodulated pulses
J
Single sideband (no carrier)
0
No modulation
8
Two or more channels of analogue information
1
Interrupted carrier
2
Keyed or digital audio modulation
9
Composite systems comprising of 1 & 2 above with 3 or 8
3
Telephony (voice or music)
X
Cases not otherwise covered
N
No information transmitted
W
Combination of the above
A
Telegraphy – for aural reception
X
Cases not otherwise covered
E
Telephony including sound broadcasting
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The emission characteristics for Radio Navigation Systems are listed below: Equipment
Emission Characteristic
ADF
N0N A1A – Long Range N0N A2A – Short Range J3E A3E A3E A8W A9W P0N
HF VHF Radio VDF ILS VOR DME SSR Loran c Radio Altimeter MLS
F G1D
Range EXAMPLE
A radio beacon has an operational range of 10 NM. By what factor should the transmitter power be increased in order to achieve an operational range of 20 NM?
ANSWER:
Four
To double the range quadruple the power
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GROUND DIRECTION FINDING (VDF) Principles of Operation
The basic VDF uses a phased array system of directional antennae based on the Doppler Principle. The indicator of the ground equipment responds to the carrier wave received.
Doppler Principle
A Doppler Navigation System is based on radar principles using frequency shift. An apparent increase in the transmitted frequency which is proportional to the transmitter velocity will occur when the transmitter moves towards the receiver. An apparent decrease in the transmitted frequency, which is proportional to the transmitter’s velocity, will occur when the transmitter moves away from the receiver.
Provides ATC with bearings of the aircraft where there is no radar and can provide a homing service to the airfield. A line of sight aid but abnormally long ranges may be experienced when signals are super refracted. Range of VDF
Range depends upon: • Power of airborne and ground transmitters • Aircraft altitude and ground transmitter elevation
Fixing
To provide a pilot with the position of the aircraft in the absence of radar, ATC must have at its disposal at least two VDFs at different locations capable of taking bearings simultaneously on the transmitted frequency The major source of cross-track error in a Doppler system is compass error.
Frequency
VHF – 118 to 137 MHz
Emission Characteristics
A3E
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Q Codes
Q Code QTE QDR QUJ QDM QGH
Meaning True track from the station Magnetic bearing from the station True track to the station Magnetic bearing to the station VDF controlled approach where the pilot is given heading and altitude to fly
Accuracy of Bearings
The accuracy of the bearing is measured in degrees. The ICAO defined classifications are: Accuracy Class A ± 2° Class B ± 5° Class C ± 10° Class D less than Class C
VDF Approaches
The aircraft needs to be fitted with a VHF radio. Using the Emergency VHF frequency (121.5 MHz) a position can be given by the emergency centre (autotriangulation).
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NON DIRECTIONAL BEACON (NDB)/AUTOMATIC DIRECTION FINDING (ADF) Principles of Operation
A radio frequency oscillator provides a carrier wave and identification which is the NDB ground signal used by the aircraft airborne equipment (ADF) to determine the direction of the transmitting station. The NDB signal transmitted is omnidirectional. The basic information given by the ADF is the relative bearing from the aircraft to the NDB NDBs transmit a surface wave that is vertically polarised. A low frequency oscillator provides the identification signal of the transmitting beacon.
Frequency
LF/MF 190 to 1750 KHz. MF not normally used due to: • Aerial size • Power requirement • Static and long wave propagation
Types of NDB
Three types: • Locators that operate around 50 watts, and have a range of 10 - 25nm • En-route that operate from 50-2000 watts, and have a range of 25 - 150nm • Oceanic that operate in excess of 2000 watts, and range is in excess of 150nm
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Emission Characteristics
Long Range Beacons
N0N A1A
Short Range Beacons
N0N A2A
Plotting
When magnetic variation is applied for NDB plotting the variation at the aircraft is taken into account. REMEMBER – True Bearing = True Heading + Relative Bearing
ADF Bearings
In order to obtain an ADF bearing on a system using sense and loop aerials, the signal must be received by both the sense and loop aerials. The combination of the polar diagrams of the loop and the sense aerial results in a cardoid polar diagram, having only one null or minimum
Loop Aerial
The ADF reception loop is always used so that the electromotive force (EMF) induced is zero. A loop aerial will receive a minimum or null signal from a transmitter when the plane of the loop is at right angles to the direction of the transmitter
Beat Frequency Oscillator (BFO)
The BFO selector switch on the ADF control panel must be in the ‘on’ position to enable the pilot to hear the IDENT of NDBs using NON A1A transmissions.
Bandwidth Control
Broad or wide bandwidth should be selected when listening to music or voice.
Tracking Accuracy
±5° (Doc 8168). Cone of silence above an NDB is 5°, as the aircraft passes the overhead the NDB needle will rotate through 180°.
Remote Magnetic Indicator (RMI)
The heading on a standard RMI is the compass heading. The RMI may have both ADF and VOR needles. The needle points to the QDM, the tail is the radial.
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AD F
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Where the RMI rose is stuck then the ADF needle will point to the relative beacons and a Relative Bearing can be calculated. EXAMPLE
If a failed RMI rose is stuck on 090° and the ADF pointer indicates 225°, the relative bearing to the station will be? Relative Bearing will be the difference between the indicated heading and the direction the ADF pointer is pointing measured in a clockwise sense. 090 to 225 = 135°
ADF Indicator – Manual Rotatable Card
The card should be rotated so that the aircraft heading is at the top of the indicator.
Drift
Where zero drift is experienced then track equals heading • If the magnetic heading decreases, the aircraft is experiencing right drift • If the magnetic heading increases, the aircraft is experiencing left drift
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Night Effect
Night Effect causes a loss of signal and fading, resulting in bearing errors from NDB transmissions. It is due to skywaves changing the plane of polarisation causing distortion of the null position and is maximum at dawn and dusk. At night the range will increase but the accuracy decrease. Night effect may cause the RMI needle to fluctuate.
Quadrantal Error
Quadrantal errors associated with aircraft Automatic Direction Finding (ADF) equipment are caused by signal bending by the aircraft metallic surfaces. • Greatest along the fuselage and the wings • Minimum at 45° to these main axes This error is compensated for.
Coastal Refraction
Errors caused by the effect of coastal refraction occur at lower altitudes and are at a maximum when the NDB is inland and the bearing crosses the coast at an acute angle. Least coastal refraction is when the signal received crosses the coast at 90°.
Mountain Effect
The mountain effect is caused by reflections onto steep slopes of mountainous terrain which may cause big errors in the bearing.
Synchronous Transmission
Where two or more beacons are transmitting on the same frequency then the measured bearing becomes the resultant of the two received signals. More apparent at: • Night • When the beacon is used outside the published range
Static Interference
Caused by local electrical storms. Near TS the greatest inaccuracies will occur.
Failure of ADF
The pilot has no indication that the ADF has failed.
Increase in Range
Transmission over the sea and lack of D layer at night increase the range. Range over the sea is greater than that overland.
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VOR AND DOPPLER VOR Principles of Operation
Two independent modulations, the reference and variable phase, are placed on a VHF frequency. The aircraft equipment measures the magnetic bearing of the station by phase comparison of these two waves.
Signal Rotation
The information carried by a signal emitted from a VOR is in what magnetic direction the signal left the VOR antenna, and the identification of the station
The variable, or directional, signal of a conventional VOR (CVOR) is clockwise; for a Doppler VOR (DVOR) anticlockwise. The Doppler effect is used to create a signal which is received by the aircraft’s VOR receiver as a frequency modulated signal. For a CVOR the variable signal (the antenna) rotates at a rate of 30 times per second which gives it the characteristics of 30 Hz AM. The reference signal is FM at 30Hz. For a DVOR the variable signal is FM the reference signal AM. • The signals are in phase on North • 90° out of phase on east • 180° out of phase on south • 270° out of phase on west On bearing magnetic north both signals are in phase
Rotating Limacon
Variable signal
+ Reference
+
-
Reference 90 phase difference = radial 090
270 phase difference = radial 270 Omni-directional Ref Signal
Reference
180 phase difference = radial 180
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EXAMPLE
If the reference phase differs 30° with the variable phase the radial from the VOR station will be: 030°
Frequency
VHF 108 to 117.95 MHz with a separation of 50kHz
Frequency allocation is between: • Terminal VOR (TVOR), a VOR with limited range used in a terminal area • ILS • Airways VOR TVOR
Uses the even first decimal and even first decimal + 50 KHz up to 112 MHz 108.00 MHz, 108.05 MHz, 108.20 MHz, 108.25 MHz etc
ILS
Uses the odd first decimal and odd first decimal + 50 KHz up to 112 MHz 108.10 MHz, 108.15 MHz, 108.30 MHz, 108.35 MHz etc
Airways VOR
The remainder of the frequency band 112 MHz to 117.95 MHz at 50 KHz spacing
Polarisation
Horizontal
Emission Characteristics
A9W
Identification
A three letter Morse identifier at 1020Hz pitch tone at least once every 30 seconds identifies a VOR. When a DME is co-located with the VOR the identifier sounds 3 times per half minute, the DME ident (1350 Hz) is at a higher pitch than the VOR ident and is broadcast only once.
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