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Radio Appreciation for PPLsRadio Appreciation for PPLs
John LinfordJohn Linford
What’s it all about?What’s it all about?
Students have to learn about aircraftStudents have to learn about aircraft
But they don’t have to learn about radioBut they don’t have to learn about radio
Yet radio is critically importantYet radio is critically important
This seminar aims to bridge the gap!This seminar aims to bridge the gap!
What we’ll coverWhat we’ll cover
Introduction to the electromagnetic spectrumIntroduction to the electromagnetic spectrum Characteristics of radio signalsCharacteristics of radio signals Radio systems used in aviationRadio systems used in aviation
– Air/Ground RTAir/Ground RT– Airfield navaidsAirfield navaids– En-route navaidsEn-route navaids– Radar systems Radar systems (in some detail)(in some detail)
– GPSGPS
You see, wire telegraph is a kind of a very, very long cat.
You pull his tail in New York and his head is meowing in Los Angeles.
Do you understand this?
And radio operates exactly the same way:
you send signals here, they receive them there.
The only difference is that there is no cat.
Albert Einstein
Electromagnetic SpectrumElectromagnetic Spectrum
An infinite continuum of frequencies…An infinite continuum of frequencies…
……from sub-audio to light (and beyond)from sub-audio to light (and beyond) The radio spectrum is in the middleThe radio spectrum is in the middle
Audio30Hz30kHz
LF30kHz300kHz
MF300Hz3MHz
HF3MHz
30MHz
VHF30MHz300MHz
UHF300MHz
3GHz
Microwave3GHz
30GHz
NDBs R/TVOR
LocaliserILS marker
ADF
DMETransponders
Glide slope
Radars
Characteristics of radio spectrumCharacteristics of radio spectrum
Radio…Radio…
– Is a form of electromagnetic radiationIs a form of electromagnetic radiation
– Travels at 300x10Travels at 300x1066m/s (186,000 miles/sec)m/s (186,000 miles/sec)
– Travels in straight lines onlyTravels in straight lines only
– Tends to be absorbed by mountains, etc.Tends to be absorbed by mountains, etc.
– Is reflected from conductive surfacesIs reflected from conductive surfaces
– Can be extensively affected by solar eventsCan be extensively affected by solar events
Radio TelephonyRadio Telephony
Civil aviation uses VHFCivil aviation uses VHF– 118.0MHz to 137.0MHz 118.0MHz to 137.0MHz – Amplitude Modulation (AM)Amplitude Modulation (AM)– 25kHz spacing (8.33kHz in the Airways)25kHz spacing (8.33kHz in the Airways)– Simple Tx and Rx equipmentSimple Tx and Rx equipment– Does the job very wellDoes the job very well
Military aviation uses UHFMilitary aviation uses UHF– 300MHz region300MHz region– Also carry VHFAlso carry VHF
Factors affecting RTFactors affecting RT
Line of sightLine of sight– Bear in mind curvature of the earth!Bear in mind curvature of the earth!– Range rule of thumb: 1.25 x Range rule of thumb: 1.25 x √√(height in feet) nm(height in feet) nm
Mountains absorb signalsMountains absorb signals Transmit power determines DOCTransmit power determines DOC Anomalous propagation effectsAnomalous propagation effects
– DuctingDucting– EsEs– Reflections from other aircraftReflections from other aircraft
The The Two at onceTwo at once problem problem
Two stations transmit simultaneouslyTwo stations transmit simultaneously– Listeners hear a squeal and distorted voiceListeners hear a squeal and distorted voice– Why?Why?
Transmitters are never on exactly the same frequencyTransmitters are never on exactly the same frequency The difference between the two TXs is in the audio The difference between the two TXs is in the audio
spectrumspectrum The two frequencies The two frequencies hetrodynehetrodyne in the receiver, producing in the receiver, producing
sum and difference productssum and difference products Assume TX-1 on 123.600MHz, TX-2 on 123.601MhzAssume TX-1 on 123.600MHz, TX-2 on 123.601Mhz
– The sum is at 247.201MHz and has no effectThe sum is at 247.201MHz and has no effect– The difference is 1kHz, an audio tone (squeal) that you hearThe difference is 1kHz, an audio tone (squeal) that you hear
RT recording systemsRT recording systems
Most airports and all en-route centresMost airports and all en-route centres Multi-track recording systemsMulti-track recording systems
– Record all radio channels, including ATISRecord all radio channels, including ATIS– Record important telephone linesRecord important telephone lines– Retained for minimum of 30 daysRetained for minimum of 30 days
In case of incidentIn case of incident– Recordings are impounded by CAARecordings are impounded by CAA
Digital recorders increasingly in useDigital recorders increasingly in use
Carlisle recordersCarlisle recorders
Airfield navaidsAirfield navaids
Non-Directional Beacon (NDB)Non-Directional Beacon (NDB) Automatic Direction Finding (ADF)Automatic Direction Finding (ADF) Distance Measuring Equipment (DME)Distance Measuring Equipment (DME) Instrument Landing System (ILS)Instrument Landing System (ILS)
NDBNDB
One of the oldest radio navigation systemsOne of the oldest radio navigation systems– Supposedly obsolete for the past 20 years!Supposedly obsolete for the past 20 years!
Simple ground equipmentSimple ground equipment– Low power LF transmitterLow power LF transmitter– 190kHz - 535kHz (1600kHz)190kHz - 535kHz (1600kHz)– Vertical antenna (omni-directional)Vertical antenna (omni-directional)
More complex aircraft equipment (the ADF)More complex aircraft equipment (the ADF)– = expensive!= expensive!
NDB/ADF principles of operationNDB/ADF principles of operation
It’s all in the antenna system!It’s all in the antenna system!– Simple antenna has figure of Simple antenna has figure of
eight response (A)eight response (A)– By adding a sense antenna, a By adding a sense antenna, a
sharp null is created in one direction (B)sharp null is created in one direction (B)– Using a Using a GoniometerGoniometer the cardioid pattern the cardioid pattern
is presented to the ADF instrumentis presented to the ADF instrument
The ADF needle connects to the Goniometer The ADF needle connects to the Goniometer and is rotated by a servo, seeking the nulland is rotated by a servo, seeking the null
A
B
NDB problemsNDB problems
Alignment of aircraft affects readingsAlignment of aircraft affects readings– Bearings are relative to aircraft directionBearings are relative to aircraft direction– Banking alters the apparent bearingBanking alters the apparent bearing
NDBs are prone to propagation errorsNDBs are prone to propagation errors– Night effect (ionospheric reflections)Night effect (ionospheric reflections)– Coastal refractionCoastal refraction– Electromagnetic stormsElectromagnetic storms
Carlisle NDBCarlisle NDB
Future of NDBsFuture of NDBs
NDBs are an anachronismNDBs are an anachronism– Better navigation systems have existed since Better navigation systems have existed since
WWIIWWII– Technically obsolete since the 1980sTechnically obsolete since the 1980s
Very cheap for airfields to implementVery cheap for airfields to implement Almost all GA aircraft have an ADFAlmost all GA aircraft have an ADF There are many NDB/DME proceduresThere are many NDB/DME procedures GPS procedures are still far far awayGPS procedures are still far far away
Morse code!Morse code!
How strange that our navaids use Morse How strange that our navaids use Morse code in this day and age!code in this day and age!
Morse code is still alive and wellMorse code is still alive and well It’s still used on navaids becauseIt’s still used on navaids because
– It’s there. It works.It’s there. It works.– Some navaids cannot carry voiceSome navaids cannot carry voice– Life expectancy of navaids has been extendedLife expectancy of navaids has been extended
It will eventually be superseded It will eventually be superseded
ADFADF
Gives ATC the bearing to/from an aircraftGives ATC the bearing to/from an aircraft It’s how you get a QDMIt’s how you get a QDM Very similar in operation to the NDBVery similar in operation to the NDB
– The aircraft’s RT transmission is the “NDB”The aircraft’s RT transmission is the “NDB”– Multiple antennas switched at high speed to Multiple antennas switched at high speed to
create a rotating cardioid create a rotating cardioid – The phase of the null represents the bearing of The phase of the null represents the bearing of
the aircraft the aircraft
Carlisle ADFCarlisle ADF
Carlisle ADF (tower)Carlisle ADF (tower)
ILSILS
Four principal componentsFour principal components– LocaliserLocaliser– Glide slopeGlide slope– Marker beaconsMarker beacons– Taxiway systemsTaxiway systems
ILS - LocaliserILS - Localiser
Gets aircraft on runway extended centre-lineGets aircraft on runway extended centre-line– 108-112MHz108-112MHz– Transmits two beams centred on the runway Transmits two beams centred on the runway
centre-linecentre-line
– Typical range ~25nm (always more than the Typical range ~25nm (always more than the Glide-Slope)Glide-Slope)
150Hz
90Hz
ILS - LocaliserILS - Localiser
Localiser antennaAbout 400m beyond stop-end
Localiser azimuthal profile
Within 17nm valid indicationsshould be obtained up to 35°
either side of runway centreline
17nm
25nm
ILS – Glide SlopeILS – Glide Slope
Places aircraft on the standard glide slopePlaces aircraft on the standard glide slope– 329-335MHz329-335MHz– Transmits two beams centred on the glide slopeTransmits two beams centred on the glide slope
– Typical range 10nmTypical range 10nm
90Hz
150Hz
ILS – Glide SlopeILS – Glide Slope
A typical glide slope antennaLocated alongside the runway, close to the normal touch-down point
ILS – Marker BeaconsILS – Marker Beacons
75MHz “fan markers”75MHz “fan markers” Outer marker, 3.5-6nm, blueOuter marker, 3.5-6nm, blue Middle Marker, ~1nm, amberMiddle Marker, ~1nm, amber Inner Marker, Cat II minima, whiteInner Marker, Cat II minima, white Middle/inner rarely installedMiddle/inner rarely installed Becoming obsoleteBecoming obsolete Replaced by T-DMEReplaced by T-DME
ILS categoriesILS categories
Cat I = 200ft DHCat I = 200ft DH Cat II = 100ft DH, 1200ft RVRCat II = 100ft DH, 1200ft RVR Cat III = 0ft DH, 0ft RVRCat III = 0ft DH, 0ft RVR
A – lands the aircraftA – lands the aircraft
B – gets it off the runwayB – gets it off the runway
C – gets it to the standC – gets it to the stand
DMEDME
A type of radarA type of radar– Aircraft sends a continuous stream of pulsesAircraft sends a continuous stream of pulses– Ground equipment receives and sends back Ground equipment receives and sends back
after a fixed delayafter a fixed delay– Aircraft times the round trip delay and computes Aircraft times the round trip delay and computes
distance: 1nm=12.36distance: 1nm=12.36µsµs– Displayed distance is slant rangeDisplayed distance is slant range– Can handle ~100 aircraft simultaneouslyCan handle ~100 aircraft simultaneously
DMEDME
CharacteristicsCharacteristics– Theoretical range 100nmTheoretical range 100nm– Accuracy Accuracy ±0.1nm±0.1nm– Aircraft Tx frequencies 1025MHz - 1150MHzAircraft Tx frequencies 1025MHz - 1150MHz– Ground reply frequency Ground reply frequency ±± 63MHz 63MHz– Ground “main delay” nominally 50Ground “main delay” nominally 50µsµs
Carlisle is set to 43Carlisle is set to 43µs (why?)µs (why?)
DMEDME
Frequency pairingFrequency pairing– There is no apparent way to select the DME There is no apparent way to select the DME
frequencyfrequency– DMEs are frequency paired with VOR & ILSDMEs are frequency paired with VOR & ILS– Pairing concept is used even when no VOR/ILSPairing concept is used even when no VOR/ILS
Carlisle is channel 44XCarlisle is channel 44X Loc: 110.7MHz, G/S: 330.2MHs, MLS: 5059.2MHzLoc: 110.7MHz, G/S: 330.2MHs, MLS: 5059.2MHz DME: Aircraft Tx on 1068MHz, ground on 1005MHzDME: Aircraft Tx on 1068MHz, ground on 1005MHz
– Hence, we think of DME as being on VHF!Hence, we think of DME as being on VHF!
DMEDME
Additional techy stuffAdditional techy stuff– Pulse pairs are used to reduce interferencePulse pairs are used to reduce interference– Pulse pair spacing is fixedPulse pair spacing is fixed
X channels: 12X channels: 12µs µs Y channels: 36µsY channels: 36µs Aircraft handles either automaticallyAircraft handles either automatically
– PRF is randomised to form a unique signaturePRF is randomised to form a unique signature Aircraft gates returns using the signatureAircraft gates returns using the signature Enters Enters tracking modetracking mode when returns match the gate when returns match the gate
Carlisle DMECarlisle DME
En-route navaidsEn-route navaids
VHF Omni Range (VOR)VHF Omni Range (VOR) NDBNDB DMEDME
VORVOR
108MHz to 118MHz108MHz to 118MHz
Always collocated with DMEAlways collocated with DME
Generally at airways intersectionsGenerally at airways intersections
Occasionally on airfieldsOccasionally on airfields
Typical DOC range 100 milesTypical DOC range 100 miles
VOR principles of operationVOR principles of operation
Transmits two separate modulationsTransmits two separate modulations– An omni-directional 30 Hz reference modulationAn omni-directional 30 Hz reference modulation– A rotating phase modulation on a 9960Hz sub A rotating phase modulation on a 9960Hz sub
carrier rotating at 1800rpm = 30rpscarrier rotating at 1800rpm = 30rps
Arranged that the two modulations are Arranged that the two modulations are exactly in phase at magnetic northexactly in phase at magnetic north
VOR receiver compares phases and uses VOR receiver compares phases and uses difference to drive the VOR displaydifference to drive the VOR display
VOR characteristicsVOR characteristics
Everything based on radials Everything based on radials fromfrom the VOR the VOR Aircraft orientation is irrelevant (cf. NDB)Aircraft orientation is irrelevant (cf. NDB) Generally unaffected by propagation issuesGenerally unaffected by propagation issues Often very well sited, with excellent rangeOften very well sited, with excellent range
– E.g. Talla VOR on top of a 2700ft mountainE.g. Talla VOR on top of a 2700ft mountain
Turnberry VOR
RNAV systemsRNAV systems
The problem with VOR/DMEThe problem with VOR/DME– Fixed locations, radial navigation systemFixed locations, radial navigation system– Only easy to use if flying between themOnly easy to use if flying between them
RNAV helps to fix this problemRNAV helps to fix this problem– Offset a VOR/DME to a convenient waypointOffset a VOR/DME to a convenient waypoint– Fly to that waypoint as normalFly to that waypoint as normal
Know what you’re doing!Know what you’re doing!– Needs careful setting upNeeds careful setting up– Risk of misinterpretation Risk of misinterpretation
FM ImmunityFM Immunity
Localiser and VOR now start at 108MHzLocaliser and VOR now start at 108MHz Band-2 FM from 88MHz to 108MHzBand-2 FM from 88MHz to 108MHz FM broadcasts are very high powerFM broadcasts are very high power
– Theoretical risk of interference with navaidsTheoretical risk of interference with navaids– Does not affect voice com (starts at 118MHz)Does not affect voice com (starts at 118MHz)
Aircraft in IFR require one FM immune NavAircraft in IFR require one FM immune Nav– External filters (very expensive!)External filters (very expensive!)– New Nav receivers (also very expensive!)New Nav receivers (also very expensive!)
Radar systemsRadar systems
Radio Detection And RangingRadio Detection And Ranging Two fundamental typesTwo fundamental types
– Primary radarPrimary radar– Secondary radarSecondary radar
Come in all shapes and sizesCome in all shapes and sizes– High power area radars (e.g. Great Dun Fell)High power area radars (e.g. Great Dun Fell)– Lower airspace radars (e.g. Warton)Lower airspace radars (e.g. Warton)– Airfield surveillance radars (e.g. Prestwick)Airfield surveillance radars (e.g. Prestwick)– PARs, ASMIs (e.g. LHR)PARs, ASMIs (e.g. LHR)– Weather radarsWeather radars
Basic principlesBasic principles
Radio signals travel at fixed velocityRadio signals travel at fixed velocity Signals are reflected by metallic objectsSignals are reflected by metallic objects So range can be obtained bySo range can be obtained by
– Transmitting a stream of pulsesTransmitting a stream of pulses– Listening for the echoListening for the echo– Time taken = distance (1nm = 12.36Time taken = distance (1nm = 12.36µs)µs)
Bearing is determined byBearing is determined by– Transmitting a narrow rotating beamTransmitting a narrow rotating beam
Basic principlesBasic principles
Fire a pulse off into spaceFire a pulse off into space– Simultaneously start a spot moving out from the Simultaneously start a spot moving out from the
centre of the screen (PPI)centre of the screen (PPI)– When the return arrives, brighten the spotWhen the return arrives, brighten the spot
The PPIThe PPI– Centre of screen is the radar headCentre of screen is the radar head– Edge of screen is radar range (or less)Edge of screen is radar range (or less)– Spot moves in same direction as radar head is Spot moves in same direction as radar head is
pointingpointing
Primary radarPrimary radar
Pulse width determines resolutionPulse width determines resolution– 1us pulse width (150 yards resolution)1us pulse width (150 yards resolution)
PRF determines rangePRF determines range– 1ms space (80 miles range)1ms space (80 miles range)
1µs 1ms
Advantages of primary radarAdvantages of primary radar
SimplicitySimplicity No equipment required on board aircraftNo equipment required on board aircraft
Limitations of primary radarLimitations of primary radar
Fixed objects give radar returns!Fixed objects give radar returns!– Rain Rain – BuildingsBuildings– Large vehiclesLarge vehicles– This clutter obscures real returns, especially close This clutter obscures real returns, especially close
to the head (and the airfield)to the head (and the airfield)
There is no identification informationThere is no identification information– ATC has to ask aircraft to turnATC has to ask aircraft to turn
Poor returns from small aircraftPoor returns from small aircraft
The fixed targets problemThe fixed targets problem
What do we know about fixed targets?What do we know about fixed targets? What might we want to do with them?What might we want to do with them?
– Why would we ever want to see fixed targets?Why would we ever want to see fixed targets?– Do we want to see rain clutter?Do we want to see rain clutter?– How might we reduce fixed target clutterHow might we reduce fixed target clutter
Moving Target IndicatorMoving Target Indicator
Fixed returns don’t move!Fixed returns don’t move!– So every return will take exactly the same timeSo every return will take exactly the same time– Each target is Each target is illuminatedilluminated with many pulses and with many pulses and
each one will take the same time to come backeach one will take the same time to come back
MTI cancels out fixed targetsMTI cancels out fixed targets– Send return pulses into a delay line with same Send return pulses into a delay line with same
delay as pulse repetitiondelay as pulse repetition– Invert the delayed signal and add it to the Invert the delayed signal and add it to the
undelayed signalundelayed signal
Moving Target IndicatorMoving Target Indicator
Some disadvantages of MTISome disadvantages of MTI– Not all relevant targets moveNot all relevant targets move
Hovering helicopters “disappear”Hovering helicopters “disappear” Slow moving aircraft such as microlights, likewiseSlow moving aircraft such as microlights, likewise
– Aircraft flying at a tangent disappearAircraft flying at a tangent disappear Tangential fadingTangential fading
MTI is generally only applied for 10 milesMTI is generally only applied for 10 miles Controller can turn off MTI on his screenController can turn off MTI on his screen
Secondary radarSecondary radar
Originally developed as IFF during WWIIOriginally developed as IFF during WWII Relies upon a transponder in the aircraftRelies upon a transponder in the aircraft Eliminates fixed target clutterEliminates fixed target clutter
– Buildings and clouds don’t have transponders!Buildings and clouds don’t have transponders!
Provides information about the aircraftProvides information about the aircraft Is used in conjunction with primary radarIs used in conjunction with primary radar Is becoming essential in CAS/TMAsIs becoming essential in CAS/TMAs
Secondary radarSecondary radar
Principles of operationPrinciples of operation– Single pair of frequencies used worldwideSingle pair of frequencies used worldwide
1030MHz TX1030MHz TX 1090MHz RX1090MHz RX
– Ground station transmits interrogation pulsesGround station transmits interrogation pulses– Transponder in aircraft responds with coded Transponder in aircraft responds with coded
information (squawk code, height, other info)information (squawk code, height, other info)– Plotted on PPI with attached information boxPlotted on PPI with attached information box
Advantages of secondary radarAdvantages of secondary radar
Positive returns, only from wanted targetsPositive returns, only from wanted targets Additional information on aircraftAdditional information on aircraft Improved performance for small aircraftImproved performance for small aircraft Improved resolutionImproved resolution Augments (does not replace) primary radarAugments (does not replace) primary radar Universally deployedUniversally deployed
Disadvantages of secondary radarDisadvantages of secondary radar
Requires a transponder in the aircraftRequires a transponder in the aircraft
Secondary radar modesSecondary radar modes
Ground transmits interleaved interrogationsGround transmits interleaved interrogations– Mode A (squawk code request)Mode A (squawk code request)– Mode C (altitude request)Mode C (altitude request)– Mode S (detailed aircraft information)Mode S (detailed aircraft information)
Aircraft responds with four octal digitsAircraft responds with four octal digits– Actual squawk codeActual squawk code– Encoded pressure altitudeEncoded pressure altitude– Optional “squawk ident” (SPI) pulse appendedOptional “squawk ident” (SPI) pulse appended
Mode SMode S
Every aircraft uniquely identifiedEvery aircraft uniquely identified– ““Hex code” linked to aircraft callsignHex code” linked to aircraft callsign– Additional operational information can be sentAdditional operational information can be sent– Selective interrogation facilitySelective interrogation facility
Mandated for class-A airspaceMandated for class-A airspace Will be progressively introduced elsewhereWill be progressively introduced elsewhere
– Major class D in the south initiallyMajor class D in the south initially– Unclear if mandated for GAUnclear if mandated for GA
Confers no benefit on the GA operator!Confers no benefit on the GA operator!
Code/callsign conversionCode/callsign conversion
Mode A sends a four digit octal codeMode A sends a four digit octal code Controller is more interested in your callsignController is more interested in your callsign
– Codes allocated when FPL filedCodes allocated when FPL filed– Ad hoc codes allocated by controllersAd hoc codes allocated by controllers
Code and callsign paired in radar databaseCode and callsign paired in radar database Aircraft callsign displayed on radar screenAircraft callsign displayed on radar screen
TCASTCAS
Traffic Collision Avoidance SystemTraffic Collision Avoidance System– An aircraft-based secondary radar systemAn aircraft-based secondary radar system– Interrogates your transponderInterrogates your transponder– Computes range, azimuthComputes range, azimuth– Obtains your height from the Mode-CObtains your height from the Mode-C– Performs collision risk assessmentPerforms collision risk assessment– Provides audible risk avoidance instructions Provides audible risk avoidance instructions
Mandated for CAT/GA over 5700kg MAUWMandated for CAT/GA over 5700kg MAUW A strong argument for transponding A+C!A strong argument for transponding A+C!
Radar antennasRadar antennas
GPSGPS
At last! A non-radial navigation systemAt last! A non-radial navigation system– Triangulates between multiple satellitesTriangulates between multiple satellites– Provides an accurate 3-dimensional fixProvides an accurate 3-dimensional fix– Navigate between any set of waypoints with easeNavigate between any set of waypoints with ease– Upload your route and away you go!Upload your route and away you go!
Moving map GPS Moving map GPS – Terrain mappingTerrain mapping– Jeppesen database (CAS, danger areas, etc.)Jeppesen database (CAS, danger areas, etc.)
GPS – some cautionsGPS – some cautions
GPS not considered a reliable system(!)GPS not considered a reliable system(!) GPS is easy to jamGPS is easy to jam GPS is owned by the US GovernmentGPS is owned by the US Government
– ““Dubbya” can turn it off any time he pleasesDubbya” can turn it off any time he pleases
As a resultAs a result– GPS not approved for primary navigationGPS not approved for primary navigation– GPS-based procedures still a distant visionGPS-based procedures still a distant vision
Use GPS in Use GPS in conjunctionconjunction with other navaids with other navaids
SummarySummary
We’ve looked atWe’ve looked at– Radio communicationsRadio communications– Airfield systemsAirfield systems– En-route systemsEn-route systems– Radar systemsRadar systems
Knowledge of these systems is important Knowledge of these systems is important and makes us better pilotsand makes us better pilots
Research the Internet for more!Research the Internet for more!
