Which of the following results from the fact that signals propagated by the ionosphere are elliptically polarized?
The correct answer is B: Either vertically or horizontally polarized antennas may be used for transmission or reception. Because signals propagated by the ionosphere are elliptically polarized (their polarization rotates as they travel), either vertical or horizontal antennas can be used effectively for both transmission and reception.
When signals travel through the ionosphere, Faraday rotation causes the polarization to become elliptical and to rotate. This means the signal doesn't maintain a single linear polarization. As a result, whether you use a vertical or horizontal antenna, you'll receive some component of the signal. This is different from line-of-sight VHF/UHF communications where polarization matching is critical. On HF, polarization mismatch is less critical because of this ionospheric effect.
Exam Tip
Ionospheric signals = Either polarization works. Remember: Because ionospherically propagated signals are elliptically polarized, you can use either vertical or horizontal antennas - polarization matching is less critical than on VHF/UHF line-of-sight.
Memory Aid
"**I**onospheric **P**olarization = **I**ndependent **P**olarization (think 'IP = IP' = Independent Polarization, either works)"
Real-World Application
You're operating on 20 meters with a vertical antenna, and you make a contact with a station using a horizontal antenna. Even though your polarizations don't match, you both receive each other well because the ionosphere has rotated the signal polarization. The elliptical polarization from ionospheric propagation means both antenna types can work effectively.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. Digital modes work fine with ionospherically propagated signals. The elliptical polarization doesn't prevent digital operation.
Option C: Incorrect. FM voice works with ionospherically propagated signals. The polarization effect doesn't prevent FM operation.
Option D: Incorrect. Antennas don't need to match polarization for ionospherically propagated signals. The elliptical polarization allows either vertical or horizontal to work.
题目解析
The correct answer is B: Either vertically or horizontally polarized antennas may be used for transmission or reception. Because signals propagated by the ionosphere are elliptically polarized (their polarization rotates as they travel), either vertical or horizontal antennas can be used effectively for both transmission and reception. When signals travel through the ionosphere, Faraday rotation causes the polarization to become elliptical and to rotate. This means the signal doesn't maintain a single linear polarization. As a result, whether you use a vertical or horizontal antenna, you'll receive some component of the signal. This is different from line-of-sight VHF/UHF communications where polarization matching is critical. On HF, polarization mismatch is less critical because of this ionospheric effect.
考试技巧
Ionospheric signals = Either polarization works. Remember: Because ionospherically propagated signals are elliptically polarized, you can use either vertical or horizontal antennas - polarization matching is less critical than on VHF/UHF line-of-sight.
记忆口诀
**I**onospheric **P**olarization = **I**ndependent **P**olarization (think 'IP = IP' = Independent Polarization, either works)
实际应用示例
You're operating on 20 meters with a vertical antenna, and you make a contact with a station using a horizontal antenna. Even though your polarizations don't match, you both receive each other well because the ionosphere has rotated the signal polarization. The elliptical polarization from ionospheric propagation means both antenna types can work effectively.
错误选项分析
Option A: Incorrect. Digital modes work fine with ionospherically propagated signals. The elliptical polarization doesn't prevent digital operation. Option C: Incorrect. FM voice works with ionospherically propagated signals. The polarization effect doesn't prevent FM operation. Option D: Incorrect. Antennas don't need to match polarization for ionospherically propagated signals. The elliptical polarization allows either vertical or horizontal to work.
知识点
Ionospheric propagation, Elliptical polarization, Faraday rotation, Antenna polarization
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.