How does the bandwidth of a transmitted signal affect selective fading?

Selective fading occurs when a radio signal arrives at a receiver via multiple paths, and the phase cancellation varies across the frequency spectrum of the signal. Because propagation conditions and multipath delays change even over a small frequency range, some frequencies within a signal may cancel out while others are reinforced. A wider bandwidth signal covers a broader range of frequencies. Therefore, it is much more likely that different parts of a wideband signal (like AM or SSB) will experience different fading conditions simultaneously, leading to severe distortion. Narrowband signals, such as CW (Morse code), occupy a very small slice of the spectrum. Because the frequency range is so small, the entire signal tends to fade in and out together rather than experiencing selective cancellation, making the effect much less pronounced.