Communication Systems Introduction

Question 1

What are some of the main components of typical communication systems?

Answer 1

1) Very High Frequency (VHF) radio
2) Ultra-High Frequency (UHF) radio
3) High-Frequency (HF) radio
4) Controller - UFCP
5) Intercom (ICS)
6) Transponder including Automatic Dependent Surveillance Broadcast (ADS-B)
7) Emergency Locator Transmitter (ELT)

Question 2

What are the 3 common radio frequencies used in aviation?

Answer 2

• HF
• VHF
• UHF

Question 3

What is the frequency range of HF waves? What are they used for?

Answer 3

3 to 30 MHz

- Used to provide long distance communications of more than 1600 km.

Question 4

What is the frequency range of VHF waves? What are they used for?

Answer 4

30 to 300 MHz

- Offers high quality, low loss, line of sight communications between aircraft and ground stations and between aircraft.

Question 5

What is the frequency range of UHF waves? What are they used for?

Answer 5

300 to 3000 MHz.
- Signals in this range have the advantage of not being subject to interference, giving clear signals of high fidelity which are easy to read.

Question 6

Is high transmission power required for HF communications?

Answer 6

Yes, because of the large distances travelled to and from the ionosphere.

Question 7

What transmission modes is a HF system capable of?

Answer 7

1) Amplitude Modulation
2) Upper side Band
3) Lower Side Band
4) DATA
5) Continuous Wave

Question 8

What are the major components of a HF communication system?

Answer 8

1) Transceiver
2) Antenna coupler
3) Controller
4) Antenna

Question 9

What does the Transceiver do?

Answer 9

It contains circuitry for both receiving and transmitting HF signals.

Question 10

What does the Antenna coupler do?

Answer 10

It alters the length of the fixed length long wife antenna so that a low voltage standing wave ratio can be maintained

Question 11

What does the controller do?

Answer 11

• The HF controller allows the aircrew to control the HF frequency and mode of operation.
• Located in one of the cockpit panels

Question 12

What does the Antenna do?

Answer 12

• Receives HF signals

- Is generally long due to the larger wavelength of the HF signal.

Question 13

What is the VHF AM frequency range and what is it used for?

Answer 13

118 to 136.975 MHz - used for civilian air traffic control band used by civilian and military aircraft interacting with ATC.

Question 14

What is the VHF FM band?

Answer 14

30 to 87.975

- Used for military communication channels between aircraft and ground troops.

Question 15

What are the average communications distances from the aircraft to ground stations?

Answer 15

30 miles at 1000 feet

123 miles at 10,000 feet

Question 16

How can greater area coverage be achieved with VHF radio?

Answer 16

Ground based repeater stations.

Question 17

What does a squelch (SQ) filter switch do?

Answer 17

• Removes a lot of background static by electronically filtering the received signal.
• Selecting the SQ OFF will allow weak signals to be heard, increasing radio range but with a log more background static.

Question 18

What are the main components of a VHF communication system?

Answer 18

• Transceiver
• Controller
• Antenna

Question 19

What does the transceiver do?

Answer 19

• Contains circuitry for receiving and transmitting VHF AM and VHF FM signals.
• Transceiver is usually located remotely in an avionics rack.

Question 20

In modern aircraft, are the VHF and UHF transceivers combined?

Answer 20

Yes

Question 21

What does the controller do?

Answer 21

The VHF controller allows the aircrew to control the VHF frequency and mode of operation.
- Located in one of the cockpit panels.

Question 22

What does the Antenna do?

Answer 22

The VHF antenna is generally located on the skin of the A/C.

Question 23

What frequency band does a UHF Communication system operate in? What is it used for?

Answer 23

225. 00 to 339.975 MHz

- Line of sight communications

Question 24

What are the typical components of a HUF communication system?

Answer 24

1) Transceiver
2) Controller
3) Antenna

Question 25

What 3 distinct services can intercom be used for?

Answer 25

1) Cockpit intercom
2) Service intercom.
3) Cabin intercom.

Question 26

What do the SSR and military IFF systems do?

Answer 26

Use a transponder that receives an interrogating signals from a ground station of 1030 MHz and automatically transmits a response in reply on a frequency of 1090 MHz.

Question 27

What are the components of the SSR/IFF system?

Answer 27

1) Control Panel
2) Transponder
3) Two Antennas
4) Encoding computer (IFF only).

Question 28

What does the control panel allow the pilot to do?

Answer 28

Input the squawk code that was given to them by ADS-B.

Question 29

What does the ADS-B do?

Answer 29

• Uses Airborne transponders, GPS data and ground based broadcasting stations that allow aircraft to know where all other aircraft are, how fast they are going, how high and on what heading.
• Transmits info to ATC and other aircraft.

Question 30

What does the UFCP allow the pilot to do?

Answer 30

• Integrates all different communication systems as well as other functionality into one controller.
• Removes a significant amount of clutter in the cockpit.

Question 31

What is an Emergency Locator Transmitter (ELT)?

Answer 31

Independent battery powered transmitter.

Question 32

What frequencies can the ELT transmit on?

Answer 32

406. 025 MHz every 50 seconds for at least 24 hours.

- May also transmit a signal on 121.5 MHz or 243.0 MHz (military emergency frequency)

Question 33

How is the ELT activated?

Answer 33

By the excessive G forces experienced during a crash.