Radio and Radar Principles

Question 1

How do radio transmissions work?

Answer 1

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.

Question 2

List the components of a transmitter

Answer 2

Microphone
Modulator
Radio frequency oscillator
Transmitting antenna

Question 3

List the components of a receiver

Answer 3

Receiving antenna
Tuner
Demodulator
Amplifier
Speaker

Question 4

What is SELCAL?

Answer 4

Selective calling radio system.

Alerts aircraft crew of incoming ground communication

Question 5

What is SELCAL procedure?

Answer 5

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.

Question 6

What is ACARS?

Answer 6

Aircraft Communications Addressing and Reporting System

Data-link system used to transmit short messages between aircraft and ground stations via radio or satellite.

Question 7

What is a VDF?

Answer 7

VHF direction finding

Determines the aircraft bearing by measuring the direction of arrival of radio transmissions from the aircraft.

Question 8

Define MTI

Answer 8

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

Question 9

What are the weaknesses of radar waves?

Answer 9

Pentrated, absorbed, reflected, refracted and attenuated

Question 10

What affects radar cover?

Answer 10

Aerial size, shape, height above ground

Question 11

What are the strengths and weakness of PSR?

Answer 11

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.

Question 12

Detail the working principles of a PSR

Answer 12

Electromagnetic pulse is transmitted during transmission phase.
Receiving phase held for set time where echoes can be received.
Rotates and repeats process in rapidly.

Question 13

Define an SMR

Answer 13

Surface Movement Radar.
Used at aerodromes to provide high refresh high accuracy readings of ground movements.
Very narrow been in azimuth.

Question 14

Detail the working principles of SSR

Answer 14

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.

Question 15

What information is contained within Mode A and Mode C?

Answer 15

Mode A - 4 digit squawk code.
Only 4096 codes available.
Mode C - Flight level/Altitude.

Question 16

List the Special purpose SSR codes

Answer 16

7700 - Aircraft Emergency
7600 - Radio Failure
7500 - Hi-Jack or other act of violence.

Question 17

What are the Advantages of SSR?

Answer 17

Less transmitter power required.
No clutter.
Identification of aircraft and vertical position.
Emergency squawk code
Not affected by size/altitude/material of the aircraft.

Question 18

What are the Disadvantages of SSR?

Answer 18

Aircraft requires transponder.
No weather info.
Label garbling.
Possible antenna shadow.

Question 19

What information is provided by Mode S?

Answer 19

Elementary - Identification/level information

Enhanced - Heading, speed, roll angle, rate of turn, vertical rate, track, ground speed, selected flight level.

Question 20

Describe the discrepancy procedure

Answer 20

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.

Question 21

What are the advantages of Mode S?

Answer 21

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.

Question 22

What are the weaknesses Mode S?

Answer 22

System are expensive.
Ground stations require optimum siting.
Dependent on aircraft avionics.
Can garble replies.

Question 23

What is ADS?

Answer 23

Automatic Dependent Surveillance.

Provides four dimensional position and weather data from the aircraft via satellite Data-link.

Question 24

What does ADS-B do?

Answer 24

Broadcasts continuously to ADS-B ground stations.
Geographical position.
Pressure altitude data.
Flight identifier.
Mode S address.
Velocity.
Other data from sensors.

Question 25

What does ADS-C do?

Answer 25

Intermittent transmission of data to contracted ANSP for remote transcontinental and transoceanic ATC services

Question 26

What are the strengths and weaknesses of ADS-B?

Answer 26

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.

Question 27

What are the strengths and weaknesses of ADS-C?

Answer 27

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.

Question 28

What is MLAT?

Answer 28

Multilateration System.

Uses SSR transponder data to derive position based on time differentials via multiple recieving antenna.

Question 29

What are the strengths and weaknesses of MLAT?

Answer 29

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.

Question 30

What is the function of Surveillance Data Networking?

Answer 30

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.