Questions and Answers
What component in the transformer rectifier unit (TRU) is responsible for converting AC to DC?
Rectifier
What effect does inserting coils into antenna elements have on the resonant frequency?
It lowers the resonant frequency
Which type of antenna is directional?
Yagi antenna
Which layer of the ionosphere reflects HF radio waves?
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Which device allows pilots to monitor their own transmission?
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During a magnetic storm, which communication quality is most likely to deteriorate?
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What does an antenna tuner in an airborne HF communication system adjust?
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For VHF and UHF equipment, which of the following antennas can be used?
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Which mode of SSR is capable of automatic altitude reporting?
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On which frequency band does VOR operate?
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Study Notes
Radio Equipment and Power
- Radio equipment requires DC power, which is obtained by converting AC output from the engine-driven generator using a transformer rectifier unit (TRU).
- The 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 resonant frequency can be electrically adjusted.
- Insertion of coils in antenna elements lowers the resonant frequency, while insertion of capacitors increases it.
Antenna Types and Applications
- Sleeve, Brown, and Yagi antennas are used for VHF and UHF equipment.
- Yagi antennas are directional.
HF Communication
- HF communication quality can be affected by magnetic storms, Dellinger phenomenon, and fading, depending on the strength of Sun's activity.
- The F layer of the ionosphere reflects HF radio waves.
Communication Systems
- The airborne HF communication system has an antenna tuner that adjusts the resonant frequency and performs impedance matching.
- A carrier wave is generated by an oscillator and modulated with a signal wave (audio).
- The modulated carrier wave is amplified to the required power for transmission.
Aviation Communication Systems
- SSR mode A can discriminate a selected "squawk" code on an aircraft's transponder panel.
- Mode C has automatic altitude reporting, and mode S can address a single specific aircraft with its unique mode-S address.
- VOR operates on VHF, providing bearing information with high accuracy, but limited to line of sight.
- DME is co-located with VOR stations to provide bearing and distance information.
Navigation Systems
- ILS components include a localizer for lateral guidance, a glide slope for vertical guidance, and marker beacons for position information.
- MTSAT provides SBAS for improved GPS navigation, CPDLC, and ADS for oceanic flights.
- INMARSAT provides better communication quality and coverage than HF voice communication, except in polar regions.
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