Advanced radio theory, circuit design, and specialized operating rules for the FCC Amateur Extra class license, based on the public-domain question pool.
45 cards · basic cards · AI-written, checked twice. Edit anything.
- What is the primary advantage of a Yagi antenna over a dipole at VHF frequencies?
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Higher gain and directivity, concentrating radiated power in a specific direction.- How does antenna gain relate to directivity and radiation efficiency?
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Gain equals directivity multiplied by radiation efficiency; gain cannot exceed directivity.- What feedline impedance is required to match a 50-ohm antenna to minimize reflections?
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50-ohm coaxial cable.- Which antenna characteristic is primarily responsible for the antenna's ability to receive weak signals?
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Effective aperture (or receiving aperture), which is related to the antenna's gain.- What is the approximate gain of a half-wave dipole at its design frequency?
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2.15 dBi (or 0 dBd by definition).- How does radiation resistance affect the efficiency of a small loop antenna?
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Low radiation resistance increases loss resistance as a proportion of total resistance, reducing efficiency significantly.- What is the polarization of a vertical antenna mounted perpendicular to Earth?
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Vertical polarization.- Which modulation technique is most resistant to ionospheric distortion on HF?
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SSB (single-sideband), as it maintains phase coherence and uses narrow bandwidth.- What is the primary limitation of PSK31 compared to CW at low signal levels?
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PSK31 requires better signal-to-noise ratio because it uses phase information, whereas CW only requires envelope detection.- Which digital mode can transmit images and is commonly used for amateur radio via satellite?
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SSTV (slow-scan television) or SSTV.- What causes the Doppler shift in a satellite communication signal?
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The relative motion between the satellite and Earth station changes the transmitted frequency.- How does atmospheric absorption affect microwave propagation above 1 GHz?
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Atmospheric oxygen and water vapor absorption increase significantly, limiting range at higher frequencies.- What is the primary advantage of using circular polarization in satellite communications?
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Circular polarization reduces the effect of Faraday rotation through the ionosphere.- Which atmospheric layer primarily reflects HF radio waves?
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The F layer (ionosphere).- What is transequatorial propagation in HF communications?
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Radio wave reflection from the ionosphere at the magnetic equator, allowing long-distance communication across the equator.
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