Radio and Radar Principles Flashcards
How do radio transmissions work?
Sound waves converted to an electrical signal which is superimposed onto a carried wave and transmitted.
The receiver removes the carrier wave and converts the electrical signal back into sound waves.
List the components of a transmitter
Microphone
Modulator
Radio frequency oscillator
Transmitting antenna
List the components of a receiver
Receiving antenna Tuner Demodulator Amplifier Speaker
What is SELCAL?
Selective calling radio system.
Alerts aircraft crew of incoming ground communication
What is SELCAL procedure?
Each aircraft has a 4 letter code which is input by the ground operator.
Encoder converts code into four designated audio tones, which are broadcasted in two pairs.
Aircraft decoder receives and sounds chine or activates alerting light.
What is ACARS?
Aircraft Communications Addressing and Reporting System
Data-link system used to transmit short messages between aircraft and ground stations via radio or satellite.
What is a VDF?
VHF direction finding
Determines the aircraft bearing by measuring the direction of arrival of radio transmissions from the aircraft.
Define MTI
Moving Target Indicator
Aids PSR display only moving targets by measuring frequency changes caused by the doppler effect.
May fade when flying at a tangent
What are the weaknesses of radar waves?
Pentrated, absorbed, reflected, refracted and attenuated
What affects radar cover?
Aerial size, shape, height above ground
What are the strengths and weakness of PSR?
Strength - Independent of aircraft equipment
Weaknesses - Large area needed, expensive to run, slant range given, clutter, can’t transmit and receive at the same time.
Detail the working principles of a PSR
Electromagnetic pulse is transmitted during transmission phase.
Receiving phase held for set time where echoes can be received.
Rotates and repeats process in rapidly.
Define an SMR
Surface Movement Radar.
Used at aerodromes to provide high refresh high accuracy readings of ground movements.
Very narrow been in azimuth.
Detail the working principles of SSR
Interrogator transmits two sets of two pulses at 1030MHz.
The first requesting mode A data at 8 microseconds apart, the second requesting mode C data at 21 microseconds apart.
The transponder replies with a 1090MHz echo of 12 pulses for mode A and 11 pulses for mode C based on the time seperation of the pulses received.
What information is contained within Mode A and Mode C?
Mode A - 4 digit squawk code.
Only 4096 codes available.
Mode C - Flight level/Altitude.
List the Special purpose SSR codes
7700 - Aircraft Emergency
7600 - Radio Failure
7500 - Hi-Jack or other act of violence.
What are the Advantages of SSR?
Less transmitter power required.
No clutter.
Identification of aircraft and vertical position.
Emergency squawk code
Not affected by size/altitude/material of the aircraft.
What are the Disadvantages of SSR?
Aircraft requires transponder.
No weather info.
Label garbling.
Possible antenna shadow.
What information is provided by Mode S?
Elementary - Identification/level information
Enhanced - Heading, speed, roll angle, rate of turn, vertical rate, track, ground speed, selected flight level.
Describe the discrepancy procedure
May be a discrepancy between mode S identifier and expected identifier.
Confirm identifier with pilot and re-enter correct identifier where necessary.
If persistent inform pilot and correct label on the situation display where possible.
Notify next control and other participating units or erroneous identifier.
What are the advantages of Mode S?
Aircraft individually interrogated.
Nealry 17 million address codes.
Permits conformance monitoring.
Provides more accurate information for STCA (Short Term Conflict Alert) and TCAS (Airborne Collision Avoidance System).
Clear presentation of aircraft labels on holding patterns.
What are the weaknesses Mode S?
System are expensive.
Ground stations require optimum siting.
Dependent on aircraft avionics.
Can garble replies.
What is ADS?
Automatic Dependent Surveillance.
Provides four dimensional position and weather data from the aircraft via satellite Data-link.
What does ADS-B do?
Broadcasts continuously to ADS-B ground stations. Geographical position. Pressure altitude data. Flight identifier. Mode S address. Velocity. Other data from sensors.
What does ADS-C do?
Intermittent transmission of data to contracted ANSP for remote transcontinental and transoceanic ATC services
What are the strengths and weaknesses of ADS-B?
Strengths: Cost effective. High update rate. High accuracy and integrity. Can be received by other aircraft. Weaknesses: Requires on board equipment. Potential outages if GPS lost. Ground stations require optimum sites for unobstructed view.
What are the strengths and weaknesses of ADS-C?
Strengths: Provides surveillance over remote areas. Low capital and maintenance costs. Weaknesses: Low reporting rates (15min) Can't be used for radar like seperation. Expensive avionics. Susceptibility to failure/overload.
What is MLAT?
Multilateration System.
Uses SSR transponder data to derive position based on time differentials via multiple recieving antenna.
What are the strengths and weaknesses of MLAT?
Strengths: Ground stations simple and cheap to maintain. Good detection independent of clutter. High update rate. Can be used in conjunction with radar. Weaknesses: Multiple sites required. Dependent on Airborne equipment.
What is the function of Surveillance Data Networking?
ANSPs gather data from multiple surveillance sources.
This allows information to be filtered in and out of control displays, helps eliminate blind spots and gives reliability through redundancy.
