Which of the following results from the fact that signals propagated by the ionosphere are elliptically polarized?

• A. Only vertically polarized antennas may be used
• B. Only horizontally polarized antennas may be used
• C. Either vertically or horizontally polarized antennas may be used for transmission or reception
• D. All antennas must be circularly polarized for optimal transmission

Answer: (C)

The correct answer indicates that either vertically or horizontally polarized antennas may be used for transmission or reception because signals propagated by the ionosphere are elliptically polarized, which means that the polarization of the signal can vary in orientation.

Elliptical polarization encompasses both vertical and horizontal polarization, meaning that a variety of antennas can effectively receive the signal. This flexibility allows for the use of different types of antennas without significant degradation in performance. As a result, operators are not restricted to using only one type of polarization, making the system more versatile and accommodating for various communications scenarios.

The other options propose limitations on antenna types that are not warranted by the characteristics of elliptically polarized signals. Notably, stating that only certain types of polarized antennas may be used would not take into account the adaptability and performance of antennas capable of handling both vertical and horizontal polarizations.