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?
- Higher gain and directivity, concentrating radiated power in a specific direction.
- How does antenna gain relate to directivity and radiation efficiency?
- 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?
- 50-ohm coaxial cable.
- Which antenna characteristic is primarily responsible for the antenna's ability to receive weak signals?
- 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?
- 2.15 dBi (or 0 dBd by definition).
- How does radiation resistance affect the efficiency of a small loop antenna?
- 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?
- Vertical polarization.
- Which modulation technique is most resistant to ionospheric distortion on HF?
- 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?
- 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?
- SSTV (slow-scan television) or SSTV.
- What causes the Doppler shift in a satellite communication signal?
- The relative motion between the satellite and Earth station changes the transmitted frequency.
- How does atmospheric absorption affect microwave propagation above 1 GHz?
- 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?
- Circular polarization reduces the effect of Faraday rotation through the ionosphere.
- Which atmospheric layer primarily reflects HF radio waves?
- The F layer (ionosphere).
- What is transequatorial propagation in HF communications?
- Radio wave reflection from the ionosphere at the magnetic equator, allowing long-distance communication across the equator.