Which of the following is a disadvantage of FM compared with single sideband?

Single sideband (SSB) modulation offers several advantages over frequency modulation (FM), particularly in the context of amateur radio communications. One significant disadvantage of FM compared to SSB is the ability to receive signals. SSB can be more selective in the way it receives signals, allowing for better rejection of adjacent channel interference. This can often mean multiple SSB signals can be received and distinguished even when they're close in frequency.

In contrast, FM tends to require a stronger signal to be clearly heard due to its wider bandwidth. As a result, FM can be less effective at picking out weaker signals or those closely spaced together, leading to the inability to receive multiple signals simultaneously. This is particularly relevant in crowded frequency bands where numerous voices are transmitting at once.

The other options mention poorer voice quality, tuning difficulties, and the generality of all previous choices being correct. However, FM typically offers good audio quality compared to SSB and is generally easier to tune into. The abilities and characteristics of SSB make it particularly favorable in certain operational contexts, which underscores why the ability to receive only one signal at a time is highlighted as a disadvantage of FM.