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Radio Transmission and Reception in Aviation

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30 Questions

What is a characteristic of intercom systems and radio systems?

They can transmit audio signals over long distances using different mediums.

What is the result of applying an electric current to an antenna?

It generates an electromagnetic field.

What is the speed at which EM waves radiate in all directions?

The speed of light.

What is the frequency range for human voice frequencies for normal speech?

90 Hz to 10 kHz.

What is the critical factor in determining the antenna length required to effectively transmit an EM wave?

The wavelength of the frequency.

What type of current is necessary to produce an expanding and collapsing field that radiates EM waves?

AC current.

Why do FM communications always use the VHF or UHF band?

Because the other bands are too small to carry sufficient FM broadcast channels

What is the primary purpose of subdividing the radio spectrum into frequency bands?

To allocate channels for specific uses

What type of waves are generated by transmitters in the VLF, LF, and MF bands?

Ground waves

What is the approximate depth that low frequencies can penetrate water?

20 metres

What is the typical power range of transmitters in the VLF, LF, and MF bands?

Hundreds of kilowatts

What is the frequency range of the USS Harold E Holt VLF communication station?

12 kHz to 27 kHz

What is the primary requirement for demodulating an incoming radio transmission?

The receive must be tuned to the same carrier frequency

Where is the antenna typically mounted on the aircraft?

On the skin of the upper or lower surface of the fuselage

What is the purpose of having 'in-use' and standby frequencies available?

To facilitate ease and speed in switching from a primary to a secondary frequency

What is a potential hazard of overexposure to radiation from operating antennas?

Serious health problems

What is a potential consequence of touching metallic objects in the radiation field near antennas?

Electric shock or RF burns

What is the typical location of the transceiver in an aircraft?

In an equipment bay

What is the primary function of the ACARS Management Unit?

To control the transmission and reception of air-to-ground and ground-to-air messages

What is the purpose of the Control Unit in the ACARS system?

To allow changing of operation modes and entering information into the data link system

What type of clock is used in the ACARS Management Unit?

GMT (Greenwich Mean Time) clock

What is the purpose of the printer in the ACARS system?

To provide a hardcopy print-out of data collected by the Management Unit

What triggers the collection of data from the Control Unit and various aircraft and avionics systems?

Events such as clearing the gate, being ready to taxi or takeoff or landing

What is an uplink in the context of ACARS?

The radio transmission path from the earth to the aircraft

What is the primary function of a communications satellite?

To create a communication channel between a source transmitter and a receiver at different locations on earth

What is the purpose of the high-gain system antenna in SATCOM?

To compensate for signal attenuation

What is the main reason why SATCOM equipment is expensive?

Because it requires a special antenna

What type of radio is installed in the aircraft for SATCOM?

UHF radio

What is the primary use of SATCOM to date?

For telephone calls and ACARS data link

What is the direction of an uplink transmission?


Study Notes

Radio Transmission and Reception

  • Intercoms and telephones allow for simultaneous talking and listening
  • Audio signals can be transmitted over long distances using wiring in intercom systems or through radio systems using the atmosphere as the transmission medium

Electromagnetic Waves

  • An electric current transmitted along a conductor develops an electromagnetic (EM) field
  • The EM field induces a small current in receiving antennas, which is amplified to reproduce the originally transmitted signal
  • Only AC produces an expanding and collapsing field that radiates EM waves
  • Antenna length is critical and dependent on the wavelength of the frequency to be transmitted


  • Human voice frequencies range from 90 Hz to 10 kHz
  • Frequency Modulation (FM) communications use the VHF or UHF band due to high bandwidth requirements
  • FM carrier wave modulation is used for broadcasting

Frequency Bands

  • A band is a small section of the radio communication frequencies spectrum
  • The International Telecommunication Union (ITU) subdivides the radio spectrum into frequency bands

Modes of Propagation

  • VLF, LF, and MF bands use antennas that maximize the production of ground waves
  • These frequencies can travel thousands of kilometers and penetrate water to a depth of approximately 20 meters
  • High power transmitters (hundreds of kilowatts) are used for these frequencies

Radio Communication in Aircraft

  • Radio control can be performed via a Flight Management System (FMC) Control Display Unit (CDU)
  • Frequency selections, tuning, and mode control can be performed through the FMC keypad and display
  • The transceiver is installed in an equipment bay, and the antenna is mounted on the upper or lower surface of the fuselage
  • "In-use" and standby frequencies are available for ease of switching between primary and secondary frequencies

Electromagnetic Radiation Hazards

  • Overexposure to radiation can cause serious health problems
  • Safe working distances must be maintained near operating antennas
  • RF burns or electric shock can result from touching antennas or metallic objects in the radiation field

ACARS Components

  • Airborne components include the Management Unit (MU), Control Unit (CU), and printer
  • The ACARS management unit controls transmission and reception of air-to-ground and ground-to-air messages through the VHF transceiver
  • The control unit allows changing of operation modes and flight crew to enter information into the data link system

Satellite Communications

  • A communications satellite amplifies and relays radio telecommunications signals via a transponder
  • SATCOM system uses a UHF radio installed in the aircraft to communicate with commercial satellites in orbit
  • SATCOM can transmit voice and data from AIRCOM, ACARS, flight-crew, passenger telephone, telex, fax, and internet

Learn about the basics of radio transmission and reception in aviation, including intercom systems and how audio signals are converted to electrical signals for transmission over long distances. This quiz is ideal for students studying for their CASA Part 66 exam.

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