13.4 - Communications Flashcards
What are the different type of radio waves.
Ground Wave, follows the curvature of the earth, <20miles (attenuated)
Direct wave, long distance comms from a ground station to a aircraft.
Sky wave, uses the earths ionosphere which refracts the radio waves back to earth. Long distance comms
Sky waves distance
Depends on the angle of the antenna projection, also due to this creates a skip zone where the waves can’t be received.
Ionosphere propagation
Different layers of the ionosphere are available. (D-F2)
Depends on time of the day.
Higher frequency used during the day as they travel further.
Layer F2 used at night.
Radio spectrum
VLF - 3-30Khz
LF - 30-300Khz
MF - 300Khz - 3Mhz
HF - 3 - 30Mhz
VHF - 30 - 300Mhz
UHF - 300Mhz - 3Ghz
SHF - 3-30Ghz
EHF - 30-300Ghz
VHF and ULF radio is
Line of sight radio, it travels slightly further than line of sight due to bending with the curvature of the earth.
VHF and ULF radio wave extension
Repeaters and increased antenna length can extend range.
Radio antenna losses
Are higher at higher frequencies
Sharp objects do what to radio waves
Detract
Radio waves travel further at
Low frequencies
What is:
MUF
&
LUF
Maximum usable frequency
Lowest usable frequency
MUF
Does not use refraction, a function of the ionosphere, as ionisation increases so does MUF.
LUF
Is a function if noise, when LUF is > MUF radio communication isn’t possible.
AM - amplitude modulation
Broadcasts at constant frequency, adds the sounds wave the base frequency (carrier wave) therefore creates a modulated signal.
FM - frequency modulation
Frequency is modulated. Tune to a set frequency ie 99Mhz, then the receiver transformer listens for the frequency and also small band differences
Clearer signal and better quality (less interference than AM)
Higher bandwidth than AM
Which radio waves travel better FM or AM?
AM because of the lower frequency.
Which radio wave is better at night and why?
AM, because FM tends to propagate through the ionosphere rather than refract back to earth.
Velocity of sound waves is dependent on?
The medium it is traveling through, atmospheric pressure & temperature
Pitch
Varies with frequency.
Human ears can hear 20mhz-20hz
Loudness depends on
The transfer of energy, greater the amplitude of the sound wave the louder it is.
ADF frequency range
200-1600Khz
NDB frequency range
190-535Khz
AM broadcast range
550-1800Khz
HF comms frequency range
2-30Mhz
Marker beacons frequency range
75Mhz
FM ration frequency range
88-108Mhz
VOR Nav (VHF) frequency range
108-118Mhz
VHF comms frequency range
118-137Mhz
Glide slope frequency range
328-336Mhz ULF
DME Frequency range
960-1215Mhz ULF
Transponder frequency range
1030 & 1090Mhz ULF
GPS Frequency
1.6 GHz SHF
Rad Alt Frequency
4.3Ghz SHF
Doppler Nav frequency
8.8Ghz SHF
Weather radar frequency
9.375Ghz SHF
Carbon microphones
High output impedance of around 100 ohms
+‘s
Robust
High output levels 250mV - 1 volt
Inexpensive compared to electromagnetic mics
-‘s
Noise due to granular movement
Poor frequency response
Requires polarising supply
Prone to mic packing
Electromagnetic microphones
Moving iron type
Dynamic type
Capacitive type
High output impedance of 100ohms
+’s
Good frequency response
Less noisy than carbon mics
Doesn’t need a polarising supply
-‘s
Low sensitivity
Expensive compared to carbon mics
More susceptible to damage
Requires a balanced input feeder system
Require mic pre amps
Headphones and loudspeakers
Generally moving iron type
Also moving coil type available
Basic TC-RX link
Sends data by electrical currents and or electromagnetic waves
Spoken word - variation in air pressure
Written word - symbols and letters
Still or moving images - light intensity
Digital data - holes in cards or tapes
If data is not in a electrical form you must?
Convert it using a transducer
Analogue signals
Continuous varying quantity
Electrical analogue message sent has the wave form as the signal it represents.
It’s continuous
It can take any value as long as it’s within system parameters
Baseband -
Is the band of frequencies covering all the signal components.
Formats must be used for systems
I.e binary
Digital baseband uses distortion to make sine peaks from on off discrete like binary to create a wave form
Analogue to digital - takes data at twice the frequency to avoid losses and coverts with a TDM
Transducer (microphone)
Converts input into electrical signal
Transmitter
Amplifies the signal I.e power level and baseband modulation
Link
Portion between TX and RX
Receiver
Amplifies the waves picked up by the antenna and demodulates to obtain the original baseband
Output transducer (speaker)
Converts electrical signal into output noise
Interference and noise
Unwanted signal finds its way to the RX
Noise - environmental noise, solar, cosmic and resistance
Ground wave (surface)
Electric current induced into the surface of the earth by electromagnetic waves.
High power losses follows the curvature of the earth.
ULF or MF
Squelch & Muting
System generates noise, to remove it uses a carrier squelch circuit which with a valid signal from a AGO voltage increase then overrides the squelch gate and allows a audio output.
Uses 8Khz noise filter
Noise limiting
Removes frequencies/ amplitude spikes thus removing unwanted noise spikes.
Long wire antenna
Terminated (non-resonant)
Not terminated (resonant)
Wire length greater than one wave length
Directional has to be pointed to where you want it to go.
The longer the wire means the directional effect changes
Half wave dipole antenna
Parallel wire which is bent opposing each other at 90 degrees
Directional antenna
Folded dipole advantages over straight dipole
Higher input impedance
Greater bandwidth
Loop antenna
One or more turns of wire wound to form a circle or square.
Dimensions smaller than the wave length
Good for direction finding
Used for confined spaces
Marconi antenna
Transmitting element, connected between antenna and ground
1/4 of wave length but because it’s connected to ground it is 1/2 wave length
Parabolic antenna
Because of small wave length in UHF and SHF a dish antenna can be used
Very directive
High gain radiation pattern
Yagi-uda antenna
One or more parasitic elements
HF antenna
How to deal with antennas which aren’t at least 1/4 wave length
Inductive loading
What is antenna gain
Gain of a antenna is a measure of the power transmitted in a particular direction with reference to an isotropie radiator
Antenna politisation types
Linear polarisation
Random polarisation
Radiated power
Radiation resistance
Why are static dischargers used
They discharge static back to the air at a constant rate so that there is no build up and dump of static
Reducing static Interference on the radio systems
VHF power
5-25 watts
VHF frequency
118-136.975Mhz
25 KHz spacing
760 available channels
Reserved VHF frequencies
118.00 arrival
118.10 tower
121.90 ground
121.75 apron
125.95 departure
121.80 delivery
121.50 emergency
HF power
100 - 400 watts
HF frequency
2 -29.999 MHz
1khz channel spacing
28000 channels
HF single side band in AM
Uses USB of radio wave to transmit to make it more efficient and less data
Selcal system
Provides aural and visual indications of calls received from ground stations
Using VHF or HF
Selcal reset
Reset key is pressed the aural and visual indications are cancelled
Satcom make up
Aircraft (antenna/LRU and interfaces)
Ground earth stations (10 worldwide)
Satellites (4)
Microphones
Convert audio into electrical signals
10-100mV
Dynamic mic
Widely used
Small loud speaker impedance approx 680 ohms and 12mV output at peak
Preamp used to transform impedance to 100!ohms and 100 mV
Electret mic
Uses a insulator to keep a trapped polarisation charge at the surface and a capacitance
Pre amp used 4V polar changes
Hand mic
Uses a pre amp
Power from the output line
ELT types
EPIRBs - maritime
ELTs - aircraft
PLBs - personal
ELT frequencies
406Mhz (UHF) satellite
Cat 1 automatically activated
Cat 2 manually activated
121.500/243Mhz UHF inactive now
ELT activation
Manual Activation
Automatic
EPIRBs - water pressure / water activated
ELTs G sensitive
ELT monitoring
406 is the active frequency monitored for by SAR satellite system
Maritime and aviation still monitor 121.500 as most ELTs have a 121.5 Homer signal
SAR signal response
Transmitter has 15,22 or 30 character unique serial number that has lots a data saved to identify the beacon
Must be registered.
If unregistered it will transmit manufacturer and serial number
121.500/243 beacon no information just a distress siren
GPS based ELTs
406Mhz
Accurate up to 100m
Can notify next of kin within 4 mins
High precision registered ELT
406 MHz
Locates to within 2km
Notifies within 2 hours
Operational testing
Some have built in self test
Others require testing
First five mins past each hour
3 sweeps maximum
ELT system
Antenna
Water switch
On/off/ arm baulked switch
LED to indicate transmission
Tether lead and float
Cannot be able to be switched on when stowed
121.5/243 performance
20/26dBm
Cycle - continuous except 406 transmission 500ms every 50 s
1420-490Hz
48 hours at -20c
406 performance
37dBm
440ms every 50s
Every 50 s
400BPS
Over 24 hours -20c
CVR
Required on multi engine MTOW >5700kg
Usually 2 hr plus recording
Flight deck capt, fo, observer/fly engineer and area mic
Captures voice and aurals
Records eng start to shut down
Min last 30 mins
Must be in easy to access location which will suffer least amount of damage
Underwater location beacon
CVR
Records from engine start to 5 mins after shut down normally
CVR power
Powered usually by stby power or battery bus
Usually auto switch function but can be manually forced to the on position
CVR performance
Withstand
3400 G
5000lbs
Deep sea pressure to 20,000ft
Temp upto 1100c
CVR ULB
Water switch operated
37.5khz
10ms pulse every second
Operated continuously for 30 days
Internal battery replaced 2-6 year periods
VOR provides
Bearing information
Aircraft angular position with respect to a selected course
To and from positions
VOR frequencies
Airway navigation - 112.00 - 117.95 all channels
Terminal area - 108.00 - 111.86
VHF
VOR line position
QDM - magnetic course to be flown to a radio station
QDR - course leading away from a radio station
VOR info
Bearing pointer - points towards station at a absolute bearing from you
Deviation bar indicates material deviation from course in 5 degree increments
VOR tuning
Can be manual or automatic
VOR is a
Medium range nav aid
100-300NM for airway nav
ADF is a
Short to medium range nav aid
ADF uses
Two loop antenna at 90 degrees to the airframe and one omnidirectional antenna
Receives non modulated morse code (continuous wave) and modulated morse code with station information
ADF direction finding
Uses loop 360 movement combined with dense antenna to find position
ADF indicator
Uses a relative bearing indicator
Absolute bearing has to be calculated by the pilot
RMI indicator (VOR & ADF)
Pointers show the direction from aircraft position toward the tuned NDB (QDM) direction magnetic (absolute bearing)
ILS frequency
Loc 108.10 - 111.95 all odd
Glide slope approx 330MHz paired with the localiser
Tuned via control panel
Even freq are reversed for VOR
ILS Loc
Flies for runway CL
90hz left band
150hz right band
Uses signal strength to determine position
If flying left of CL the needle would point right to indicate to flying right to intercept
ILS Glide slope
Typical 3 degree slope
90hz upper band
150 hz lower band
Pointer shows direction to fly
Frequency 329.15-335MHz
ILS marker beacons
75 MHz freq 6000ft
Outer - blue 400hz approx 7nm
Middle - amber 1300hz approx 1nm
Inner - white 3000hz approx 200-1500ft
Lights and aural indication
Shows distance to runway threshold
Flight directors
Takes computer data to give the pilots command bars to fly a route
DME
Gives slang distance to a ground station in NM
DME frequency
Around 1GHz (UHF) usually paired with VOR station (VHF)
DME operation interrogator transmitter and ground station transmitter
Interrogator transmitter operates on one frequency and ground station transmitter operates on another frequency.
GST is always 63MHz above or below Interrogator
DME range
300nm
DME/VOR navigation
Lateral and distance to calculate a position fix
ILS/DME
Distance to touch down, displayed on the PFF
FMS DME useage
Uses two DME stations preferably at 90 degrees to create a fix
DME tuning
Automatic FMS tuning
Manual FMS tuning
Manual tuning via radio control panel
RNAV
Uses VOR bearing, DME slant ranging and barometric altitude.
FMS functions
Navigation
Performance
Guidance
FMS Data base
Updated every 28 days
MIX IRS position accuracy
2NM/h
Radio position accuracy
.3NM
GPS accuracy
<.3NM
FM position accuracy
En route 3.5NM
Terminal 2NM
Approach .36NM
FMS
Provides lateral and vertical navigation with full performance management
Flight plan take off and approach
SID - standard instrument departure
STAR - standard arrival route
GPS & GNSS
Uses DME theory to create position fixes from satellites in space
Based on UTC time and known positions of the satellites in orbit.
3 satellites for a position fix and 4 to provide altitude
GPS satellites
24 in use in six different orbit patterns 12 hours per orbit
3 or more spare satellites in orbit
GPS control segments
Master stations and auxiliary stations 16’in total
Help manage and monitor satellites
GPS User segment
Aircraft etc
GPS ground based augmentation
Can be used for ILS using GPS fox for touch down zones
Highly accurate
Datalink
Used to reduce voice communications between aircraft and the ground.
CPDLC
ACARs
Datalink types
Simplex - communicates in one direction only
Half duplex - communicates both ways but only one way at a time
Duplex - communicates both ways simultaneously.
ATC transponder
Provides primary and secondary surveillance radar and other aircraft interrogation and pings to identify locations
ATC transponder modes
A - aircraft identification
B- ident and altitude
S- ident, altitude and communication link
ATC
1030MHz interrogation signal
Responds with 1090MHz squirter
Squawk code will give a coupler lock
ATC transponder ident
24 Pin programmed code - country of registration then unique code
ADS-B
Allows extra precision of air traffic and weather overlays to the ground and airborne
ADS-B
GPS based system which communicates, aircraft type, speed, attitude and altitude also paired with mode s
Overlays weather
TCAS legal requirements
Aircraft with a MTOW >5700kgs and more than 19 pax
TCAS 1 10-30 pax
TCAS 2 30 pax plus
ACAS is the
International standard for the equipment requirement set by ICAO
ACAS 1
TA only
ACAS 2
TA/RA
ACAS 2 inputs needed
Aircraft address code
Air to air mode S
Own aircraft’s max cruising true air speed
Pressure altitude
Rad alt
TCAS operation
Uses 1030/1090Mhz interrogation and response on Mode S but also communicates with modes A and C
Vertical TA/RA only
TCAS indications
Can indicate traffic above and below non shaded Diamond - normal traffic
Shaded diamond - proximate traffic
Solid amber circle - traffic advisory (intruder)
Red solid square - resolution advisory (threat)
TCAS antenna
Directional antenna
One upper skin
One lower skin
TA and RA calculations
Based on the closest point of approach
20-48 seconds for a TA
15-35 Seine’s for a RA
Depends on aircraft altitude
TCAS transponder modes
Standby
Transponder
TA only
TA/RA
TCAS alerts
Traffic
RA climb or dive
Clear of conflict
TCAS
Can process ADSB data
TCAS PFD indications
ADI bars to indicate unsafe areas
VSI Green and red to indicate safe/unsafe zone
Traffic awareness for light aircraft
Traffic information service (TIS) - uses ADS-B
Traffic advisory system (TAS) - mode S system
FLARM
For gliders traffic
Weather radar operation
Emits microwave pulses through a directive antenna which picks up the return signals.
Range is determined by the time taken for the echo to return.
Microwave 9.4GHz
125W - 65 kW 180-400 pulses per second
Up to 20 sweeps a minute
Strength of the echo returned from the water droplets in the cloud determine the water droplet density.
Weather radar returns
Green - light weather
Amber - moderate weather
Red - severe weather
Magenta - turbulence
Weather radar displays
Weather
Or
Terrain
WXR turbulence detection
Pulse waveforms show that the echo frequency differs from the transmitted pulse caused by the Doppler effect.
WXR radar antenna
Parabolic antenna with tilt and sweep capabilities
WXR radar stabilisation
Stabilised in pitch and roll by a IRS feed or a vertical gyro
Mechanical limits
Roll +_ 43 degrees
Pitch +_ 25 degrees
Tilt +_15 degrees
Azimuth drive
Antenna capable of scanning a total azimuth of +45 degrees to + 90 degrees 20 times a minute
WXR radar tilted to ground 15 degrees
To paint ground radar returns
WXR radar safe zone
4 metre radius
240degree radius
Rad Alt
Projects wave towards terrain below which is reflected back to the aircraft, it uses the time to calculate distance.
Rad Alt
Frequency 4.3 GHz
Rad Alt operation
Rising runway from 200ft
Audio call outs from 400ft
MLS
Was designed to replace ILS, greater accuracy than ILS, requires less bulky equipment
Five functions
Approach azimuth
Back azimuth
Approach elevation
Range and data communications
Very low frequency and hyperbolic navigation
Decca
Oméga
LORAN
Doppler
INS
Principle uses 2 accelerometers and rate gyro
1 N/S
1 E/W to produce outputs for movement.
Amplified then through two interrogator and a computer which knows the initial position can produce coordinates for new position
Importance of keeping the accelerometers level
Prevents inaccuracies being induced by pitch and roll of the airplane.
The accelerometers are mounted so that they will stay level when the aircraft attitude changes
INS earth and transport compensation
Made by the computer system to keep the navigation data accurate
Latitude and longitude
Latitude - north to south 0 degrees is the equator
Longitude is east to west
IRS make up
Three laser gyros and three accelerometers
IRS
Sensing all pitch and roll movements of the aircraft unlike INS
IRS modes
Off
Align
Nav
Attitude
IRS config
3 Accelerometers and 3 laser gyros
Act on all three axis
ACARs - aircraft communication and reporting system
Uses radio stations to send automated or manually drafted messages between ground stations and aircraft
ACARs stations
Uses stations for round the world
Europe
Asia
America
Oceanic
Via VHF or satcom
ACARs frequency
Arinc acars 131.725
Can auto tune if the frequencies are busy
ACARs
OOOI events through key flight phases to report back
ACARs manual message
Preamble - 34 characters
Message - 220 characters
Trailer - 7 characters parity and verification
