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

The correct answer indicates that either vertically or horizontally polarized antennas may be used for transmission or reception due to the elliptical polarization of signals propagated by the ionosphere.

When signals are elliptically polarized, they exhibit characteristics of both vertical and horizontal polarization. This means that the signal has components that can be received effectively by antennas designed for either orientation. As a result, operators are not limited to a specific antenna polarization, which gives them flexibility in choosing their equipment based on availability or other considerations. This adaptability is particularly useful in amateur radio, where diverse setups can be utilized to achieve reliable communication.

Other choices do not accurately represent the implications of elliptical polarization. For instance, the usability of digital modes or FM voice is not inherently affected by the polarization of the signal itself, and rules about antenna polarization do not require both antennas to be oriented identically when using elliptically polarized signals. Thus, the ability to utilize antennas of different polarizations enhances operational versatility in amateur radio communications.