VHF/HF Communication Systems Chapter 1

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Questions and Answers

What is the primary function of the SELCAL system in aircraft communication?

To enhance the accuracy of aircraft position reporting

To improve the clarity of voice communications in high-noise environments

To enable pilots to communicate with multiple control towers simultaneously

To automatically alert pilots to specific aircraft calls, bypassing the need for continuous radio monitoring (correct)

Which of the following is NOT a feature of the ELT-RESCU 406?

A plastic water bag

A lanyard cord for attachment to a raft

A long, erectable antenna

A built-in GPS receiver for precise location data (correct)

A battery that is waterproof

What is the main purpose of the liquid container in the ELT's land operation?

To serve as a buoyancy aid for the ELT if submerged in water

To activate the water-activated switch and power the beacon (correct)

To provide a source of drinking water for survivors

To cool the battery and prevent overheating

Which of these frequency bands is NOT used by the ELT-RESCU 406 for transmitting distress signals?

156.8 MHz (C) Signup and view all the answers

What do the letters "SELCAL" stand for?

Selective Call (C) Signup and view all the answers

In the SELCAL system, what component delivers the received audio to the decoder?

The VHF/HF transceiver (E) Signup and view all the answers

What is the purpose of the "Alert Signal" in the SELCAL system?

To activate the SELCAL lamp/switch in the cockpit (F) Signup and view all the answers

In the context of ELT operation, what does 'NM' likely stand for?

Nautical Miles (C) Signup and view all the answers

What is the maximum duration of a standard ELT transmission?

48 hours (A) Signup and view all the answers

When an ELT is activated for a water operation, what is the most crucial action to take after placing it in the water?

Unroll the lanyard cord and tie it to a raft (D) Signup and view all the answers

What is the primary use of Very High Frequency (VHF) communication in aviation?

Air traffic control (ATC) (A) Signup and view all the answers

What is the frequency range of VHF communication for aviation purposes?

118-136 MHz (D) Signup and view all the answers

Which of the following is NOT a characteristic of VHF communication?

Wide geographical coverage (D) Signup and view all the answers

What factor(s) affect the maximum range of VHF communication between two aircraft?

The height of the transmitting and receiving antennas (A) Signup and view all the answers

According to the content, what is the future of communication in aviation predicted to be?

Increased use of data transfer for communication (C) Signup and view all the answers

Which of the following factors does NOT affect the range of VHF transmission?

Frequency of operation (C) Signup and view all the answers

What is the primary use of HF communication?

Air Traffic Control (ATC) (C) Signup and view all the answers

Which component of the HF system matches the antenna to save power?

Coupler (D) Signup and view all the answers

Which factor is LEAST likely to affect HF transmission range?

The height of the aircraft (C) Signup and view all the answers

What type of wave does HF communication primarily utilize?

Sky wave (A) Signup and view all the answers

How is audio from VHF transmission routed for voice communications?

To the flight interphone system (D) Signup and view all the answers

What specific frequency range does HF communication typically operate within?

2-22 MHz (C) Signup and view all the answers

Which system component provides microphone audio input for VHF voice transmission?

Control panel (C) Signup and view all the answers

What causes loss of HF voice communication under certain circumstances?

Disturbances in the ionosphere (D) Signup and view all the answers

In VHF transmission, what does the RF-Coax line connect?

Transceiver and antenna (B) Signup and view all the answers

Which variable is NOT a factor affecting the range of VHF transmission?

Time of day (D) Signup and view all the answers

What is the purpose of the coupler in the HF system?

To match the antenna for efficient signal power (A) Signup and view all the answers

In HF communication, which of the following is considered the primary mode of communication?

Sky wave communication (C) Signup and view all the answers

What condition is LEAST likely to influence HF transmission range?

Height of the receiver (D) Signup and view all the answers

Which of the following components is responsible for providing the frequency selection in an HF system?

Frequency and Power control panel (D) Signup and view all the answers

What is the primary characteristic of VHF communication regarding its signal propagation?

It is functionally limited to line of sight and direct wave propagation. (C) Signup and view all the answers

What frequency range is considered the VHF band in aviation?

118-136 MHz (D) Signup and view all the answers

In terms of transmitter and receiver antenna heights, what is the main variable affecting VHF range?

The relative height of the transmitter and receiver antennas. (A) Signup and view all the answers

Which scenario best describes the primary use of VHF communication in aviation?

Voice communications between air traffic control and aircraft. (B) Signup and view all the answers

What can be inferred about the future of aviation communication systems?

Voice communication will still play a significant role in certain regions. (D) Signup and view all the answers

Study Notes

Chapter 1: VHF/HF Communication Systems

VHF communication relies on line-of-sight propagation, making it suitable for short-range air-to-air and air-to-ground voice communication.
VHF is primarily used for Air Traffic Control (ATC).
The VHF frequency band is 118-136 MHz.
VHF communication range is affected by transmitter and receiver antenna heights, and obstacles in the path.
The range formula is R = 1.25 * √(H_r + H_t), where R is in nautical miles, and H_r and H_t are the receiver and transmitter antenna heights in feet.
An example calculation: A VHF signal transmitted from an aircraft at 12,000 ft will have a range of approximately 255 nm to another aircraft flying at 9,000 ft.
The factors affecting VHF transmission range include transmission power (both aircraft and ground station), antenna height, and obstacles.
A VHF system includes a frequency control panel, transceiver (transmitter and receiver), antenna, and RF coax line.
The frequency selection is from the control panel.
Flight interphone systems provide microphone (MIC) audio input for voice transmission.

HF Communication

HF communication primarily uses sky wave propagation, enabling long-range air-to-air and air-to-ground voice communication, crucial for global air traffic.
HF is also used for ATC.
The HF frequency band is 2-22 MHz.
Factors affecting HF range include transmission power, time of day, season, ionospheric disturbances, geographical location, and frequency.

Selective Calling (SELCAL)

Pilots on long-haul flights used to listen continuously for their call sign, which was tiring.
The SELCAL system allows pilots to mute the receiver until ATC transmits a code specific to their aircraft.
The SELCAL system has a decoder (with five channels), tone selector, and various alarms (lights, bells, or both).
Each VHF/HF transceiver used in voice communications delivers received audio to the decoder.
When the relevant code is received, the SELCAL system activates an alarm (light, bell, or both), instructing the crew to de-select the mute function and communicate normally.
SELCAL tones have allocated frequencies (e.g., RED "A" at 312.6 Hz, etc.)

Emergency Locator Transmitter (ELT)

ELTs are radio devices carried on aircraft for emergency use.
Activation of an ELT sends a radio signal aiding in locating crash sites and assisting rescue personnel.
The Honeywell RESCU 406 ELT is programmable and operates in both water and on land, and has a water-proof battery and long erecting antenna.
The ELT operates on specific frequencies for civil and military rescue (121.5 MHz for civil and 243.0 MHz for military).

Water Operation

The ELT's lanyard is tied to a raft.
The ELT is put in water.
The ELT automatically activates and starts emitting distress frequencies.

Land Operation

The antenna needs to be erected without obstacles.
Pouring liquid into the container for the ELT activates a switch, ready for transmission.
The ELT has a liquid casing for use on both land and water.
The ELT is correctly placed and held for efficient signal transmission.
ELT's typical operation duration is 48 hours.

Example Calculations

An example calculation for current consumption of an ELT battery operating for 24 hours with a 240 mAh rating is 10 mA.

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Description

This quiz covers the fundamentals of VHF communication systems, including their operation, applications, and the factors affecting their range. Learn about the frequency band, range calculation, and essential components of VHF systems used in air traffic control. Test your knowledge on this vital aspect of aviation communication.