Antennas and Feed Lines Flashcards
7 cards from real HAM practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Antennas and Feed Lines flashcards as text
What is the radiation pattern of an isotropic antenna?
Answer: A perfect sphere — equal radiation in all directions
An isotropic antenna is a theoretical point source that radiates equally in all directions, forming a perfect sphere.
What is the significance of the 1:1 SWR condition on a transmission line?
Answer: Maximum power transfer occurs with no reflected wave
A 1:1 SWR means the line is perfectly matched — all forward power is absorbed by the load with no reflection.
A log-periodic dipole array (LPDA) antenna is best described as:
Answer: A broadband directional antenna with moderate gain across a wide frequency range
An LPDA is a broadband directional antenna providing consistent moderate gain across a wide frequency range, widely used for HF communication.
What is the effect of ground conductivity on the performance of a quarter-wave vertical antenna with radials?
Answer: Higher conductivity reduces ground losses and improves radiation efficiency
Higher ground conductivity reduces the resistive loss in the ground return current path, improving the efficiency and gain of a vertical antenna.
What is the advantage of using a terminated folded dipole (T2FD) antenna?
Answer: Broadband operation with low SWR across a wide frequency range due to the terminating resistor
The T2FD uses a terminating resistor to achieve a broad, low-SWR frequency range at the expense of efficiency, making it useful for wideband receive or transmit applications.
What is the main advantage of a rhombic antenna over a Yagi for long-distance HF communication?
Answer: Much broader bandwidth covering multiple HF bands
A rhombic antenna is inherently broadband, covering many HF frequencies with useful gain, unlike the narrowband Yagi.
What occurs when a transmission line is exactly one half-wavelength long, regardless of its characteristic impedance?
Answer: The input impedance equals the load impedance (the line is transparent)
A half-wavelength transmission line repeats the load impedance at its input, making it electrically transparent — the input impedance equals the load impedance.