A radio station has two channels. One is AM at 1020 kHz and the other FM at 89.5 MHz. For good results you will use
Shorter antenna for the AM channel and longer for the FM.
For AM channel of 1020 kHz, ground wave propagation is used for which antenna need not be very tall.
For high frequency FM of 89.5 MHz, space wave communication is used for which very tall antennas are needed.