Yeah but neither is optimized. FM goes all the way from 88-108mhz so this encompasses a large change in antenna length. AM is incredibly low in frequency by comparison, but it is nearly a 3:1 frequency multiplication-------about 500khz to about 1500 khz. A quarter wave whip on 1500khz, more or less, would be about 160 feet!!! (This is more or less depending on radiator construction). A 500khz whip would be 3X that height!!!!
By the same reasoning, an 88 -108 mhz FM whip would be around 33-27 inches
