Radio Communication and Antenna Fundamentals

Radio Equipment Power

• Radio equipment requires DC power to operate.

Transformer Rectifier Unit (TRU)

• AC output of the engine driven generator is converted to DC by the TRU.
• TRU consists of a transformer, a rectifier, and a smoothing circuit.

Antenna Characteristics

• The resonant frequency of an antenna is determined by the antenna element length.
• The antenna's characteristic (resonant) frequency is electrically adjustable.
• Insertion of coils in antenna elements lowers the resonant frequency.
• Insertion of capacitors makes the resonant frequency higher.

Antenna Tuner

• Airborne HF communication system has an antenna tuner in the antenna circuit.
• The antenna tuner adjusts the resonant frequency and performs impedance matching.

Antenna Types

• Sleeve antenna, Brown antenna, and Yagi antenna are used for VHF and UHF equipment.
• Yagi antenna is a directional antenna.

Ionosphere and HF Communication

• The F layer in the ionosphere reflects HF radio waves.
• HF communication quality can be deteriorated by magnetic storm, Dellinger phenomenon, and fading depending on the strength of Sun's activity.

Radio Wave Transmission

• A carrier wave is generated by an oscillator.
• The carrier wave is modulated with a signal wave (audio), and the modulated carrier wave is amplified to the required power for transmission.

Side Tone Circuit

• The side tone circuit allows pilots to monitor their own transmission.
• Transmission signal is partially fed back to the receiving system for this purpose.

Radar Frequencies

• Detection capability of a high-frequency microwave is excellent, but its attenuation is high.
• The airport surface detection equipment (ASDE) operates on SHF (Super High Frequency).
• The air route surveillance radar (ARSR) and the airport surveillance radar (ASR) operate on UHF.

SSR Modes

• SSR mode A is capable of discriminating a "squawk" code selected on the aircraft's transponder panel.
• Mode C has a capability of automatic altitude reporting.
• Mode S is capable of addressing a single specific aircraft with its unique mode-S address.

Navigation Systems

• VOR operates on VHF, providing excellent accuracy of bearing but with limited coverage to line of sight.
• DME is commonly co-located at VOR stations to provide aircraft with bearing and distance information.
• RNAV routes are established along waypoints based on the bearing and distance information from VOR/DME.

ILS Components

• Basic ILS components are a localizer for lateral guidance, a glide slope for vertical guidance, and marker beacons for position information.

MTSAT and Satellite-Based Augmentation System

• MTSAT provided SBAS (Satellite-Based Augmentation System) for improved accuracy and reliability of GPS navigation.
• MTSAT also provided Controller Pilot Data-Link Communication (CPDLC) and Automatic Dependent Surveillance (ADS) for oceanic flights.
• SBAS function is being transferred to QSS (Quasi-Zenith Satellite System).

INMARSAT Communication

• The quality and coverage of communication by INMARSAT are much better than HF voice communication, except in polar regions.