Equipment Flashcards
Radio waves are used in the following areas of ATC
Voice Communication VHF/ UHF
Navigation VOR /NDB
Surveillance systems
Weather radar
Data transmission
According to Ampère’s law, an
electric current produces:
a magnetic field perpendicular to the
flow direction
Radio waves are a form of:
electromagnetic energy
that are similar in behaviour to light waves
What is the speed of light?
300,000,000 meters per second (c)
Radio waves are capable of:
passing through a vacuum
Travel in straight lines (generally)
Invisible
Intangible (Can’t touch it)
Inaudible without specialist equipment
What is Audio?
These movements of air make the eardrum
vibrate and mimic the air which is moving, thus
the receiving person hears the propagated tone
Why is Audio limited in range?
how loud one can speak and absorption by materials within its range.
How do we overcome absorbtion?
very high
frequencies are used which can be propagated
over large distances, but are not within the
audio spectrum
What is osscilation?
how a wave changes from a
maximum to a minimum. Shown as a sine
wave.
What is amplitude?
“The maximum displacement or value attained
by the wave from it’s mean value during a cycle”
Wavelength
The distance in meters or part of a meter between
corresponding points in consecutive waves
Scientifically represented by lambda
Frequency
“The rate of repetition of the cycle in one second
where one cycle per second is known as one Hertz.”
Hertz numbers
Kilohertz (KHz) - where 1 KHz = 1,000Hz
Megahertz (MHz)- where 1 Mhz = 1,000,000Hz
Gigahertz (GHz) - where 1 GHz = 1,000,000,000Hz
Velocity definition
“The speed in a given direction.”
Velocity of electromagnetic waves in a vacuum is?
a constant 300,000,000
meters per second
Velocity =
frequency x wavelength
“The Local Oscillator”
A Carrier Wave is an electro-magnetic wave which can be modulated (varied) and is produced by a device
carrier wave is modulated (varied) in direct proportion to…
the signal that is to be transmitted
modulation can change either:
the amplitude or the frequency of the carrier wave.
How does modulation work?
The audio signal is fed into a Modulator, which
combines the carrier wave with the audio wave.
AM-
amplitude modulation
FM-
frequency modulation
Advantages of FM:
Resilience to noise
easy to apply modulation at low power
use of efficient RF amplifiers
Advantages of AM:
Stronger stations can override weaker
Control tower can “talk over”
heterodyne will be heard
What is a quarter wave aerial?
Using the top of the positive part of this cycle is
known as a half-wave aerial, or using the first
90deg of the cycle
The EMF radiates perpendicular to…
the antenna, so with a vertical antenna, the EMF is horizontal; with a horizontal antenna the EMF radiates vertically.
A radio wave reduces in strength with range or time
from the point of transmission.
This is due to:
The ever-expanding wave front.
The medium through which the wave is passing resists the passage of energy passing through it.
As a signal is attenuated, it’s amplitude…
decreases, but the wavelength and frequency remain unchanged
Higher frequency, greater attenuation,
shorter range
The radio waves are divided according to:
the frequency of the transmission into
internationally recognised bands
Upper and lower end of waveband scale:
Electrical energy
(lower end of scale)
Infra red energy
(upper end of scale)
Very low frequency:
Very Low Frequency
VLF 3 - 30 KHz 100km - 10km
Long range communications.
Requires immense aerials and high transmitter power.
Very prone to static interference.
Very long range navigation aids.
Low and Medium frequency:
Reliable, long range communications.
Requires large aerials and high transmitter power.
Prone to static interference and night effect.
Very congested waveband.
NDB.
Some radio broadcasts.
High frequency:
Long range communications by day and night limited
by diurnal and seasonal variation of the ionosphere.
Requires smaller aerials and transmitter power.
Suffers from static interference and fading.
Optimum operating frequency varies diurnally.
Long distance wireless telegraphy.
RTF communications.
Very high frequency and ultra high frquency
Line of sight communications.
Maximum range dependent upon aircraft height
and aerial height.
Small aerial and transmission power.
Free from static interference and easy to suppress
on aircraft.
Prone to ducting.
Wavebands become congested.
RTF, ILS, VOR, VDF, Surveillance Radar.
Super high frequency and Extremely high frequency
Short range communications.
Severe attenuation.
Precision, Surveillance and Airborne weather Radar.
Radio altimeter.
VHF and higher frequencies propagate on:
straight paths
DUCTED WAVE
A marked temperature inversion plus a rapid decrease in humidity may form a duct within which VHF, UHF and SHF wavebands can unusually travel long distances
What is an indirect wave?
the low frequencies will bend
around objects and be heard a great distance from the source. The low frequency means less attenuation
Where do we use Radar?
Area control
Approach control
Aerodrome control (AIR & GROUND)
Speed of sound in m/s:
330m/s
RADAR stands for:
Radio detection and ranging
Primary radar
‘A SYSTEM THAT USES REFLECTED RADIO SIGNALS’
The position of the object that reflected the energy is
determined from:
The direction that the radar aerial was pointing, and
The time between transmitting the pulse of energy and receiving an echo.
ATC Radar is in that part of the waveband spectrum between:
1mm to 100cm
PSR Blip
The visual indication, in non symbolic form,
on a situation display of the position of an
aircraft obtained by primary radar.
Wavelength for surface movement radar:
2-3cm
Wavelength for primary approach radar:
3cm-10cm
Wavelength for primary area radar:
23cm-50cm
A typical approach radar may
transmit around…
1200 pulses per second
Position indication
A generic term for the visual indication, in nonsymbolic and/or symbolic form, on a situation
display of the position of an aircraft, aerodrome
vehicle or other object.
POSITION SYMBOL
A visual indication in symbolic form, on a situation
display, of the position of an aircraft, aerodrome
vehicle or other object obtained after automatic
processing of positional data derived from any
source.
RADAR CONTACT
The situation which exists when the radar position of a particular aircraft is seen and identified on a situation display. (ICAO
RADAR CONTROL
Term used to indicate that radar-derived information is employed directly in the provision of air traffic control service.
SITUATION DISPLAY
An electronic display depicting the position and movement of aircraft and other information as required. (ICAO)
Every primary radar system must be capable of:
transmitting energy in a suitable form, (transmission)
receiving energy which has been reflected by objects within the operational range of the system, (Reception)
displaying information to the controller. (Display)
Trigger Unit (Master Timer)
device whose output is used to initiate action.
Transmitter Unit
The output of the Transmitter is a series of pulses of
radar energy. Each pulse thus produced is delivered
to the aerial.
The Modulator Unit
Every time the modulator unit is fired by the
trigger unit it sends a high power, high voltage
pulse to the transmitter.
RECEPTION BLOCK
The signal reception block detects energy
reflected from objects. The weak signal must be
amplified and suitably treated by the HIGH GAIN
LOW NOISE RECEIVER
SECONDARY SURVEILLANCE RADAR
A SYSTEM OF RADAR USING GROUND
INTERROGATORS AND AIRBORNE
TRANSPONDERS TO DETERMINE THE POSITION
OF AIRCRAFT IN RANGE AND AZIMUTH, AND
WHEN AGREED MODES AND CODES ARE USED,
HEIGHT AND IDENTITY ALSO.
what are the frequencies of secondary radar?
interrogator- 1030MHz
transponder- 1090MHz
The Interrogator Process
The interrogator communicates a request for
identification information by transmitting MODE A
pairs of pulses.
For vertical position information the interrogator
transmits MODE C pairs of pulses.
The difference between Mode A + C is the timing
between the pulses
The Reply Process
The aircraft transponder recognises the
interrogator Mode by the time interval
The transponder response to an interrogation
consists of a train of pulses containing binary
bits of information.
How many possible squawk codes are there?
4096
CCAMS
Centralised Code Assignment and Management System
Types of squawk code
discrete code
non discrete code
special code