Which statement is true regarding AM compared to FM in terms of power and length of reach?

Which statement is true regarding AM compared to FM in terms of power and length of reach?

• A. AM generally requires less power and can reach farther
• B. AM requires more power and reaches farther
• C. AM uses more spectrum and reaches shorter distances
• D. AM uses less spectrum and reaches shorter distances

Answer: (A)

The main idea is how propagation works for AM versus FM. AM signals sit in much lower frequencies, which lets them travel as ground waves along the surface and, after dark, bounce off the ionosphere (skywave). Those propagation paths let AM reach faraway locations with relatively modest transmitter power. FM, on the other hand, operates at higher frequencies where signals travel mainly by line of sight and are more quickly attenuated with distance and obstacles, so achieving the same coverage generally needs more power and is limited to shorter ranges. So AM’s ability to cover larger distances at lower power comes from its propagation characteristics at lower frequencies, not from using more spectrum. The other statements conflict with these propagation facts: FM uses significantly more bandwidth than AM, and the reach is not inherently longer for FM under typical conditions.

The main idea is how propagation works for AM versus FM. AM signals sit in much lower frequencies, which lets them travel as ground waves along the surface and, after dark, bounce off the ionosphere (skywave). Those propagation paths let AM reach faraway locations with relatively modest transmitter power. FM, on the other hand, operates at higher frequencies where signals travel mainly by line of sight and are more quickly attenuated with distance and obstacles, so achieving the same coverage generally needs more power and is limited to shorter ranges.

So AM’s ability to cover larger distances at lower power comes from its propagation characteristics at lower frequencies, not from using more spectrum. The other statements conflict with these propagation facts: FM uses significantly more bandwidth than AM, and the reach is not inherently longer for FM under typical conditions.