Inspired by this question:

https://electronics.stackexchange.com/questions/39423/what-is-the-basic-difference-between-am-and-fm-radio

I got to wondering: If I put my FM radio on some radio channel (Let's just say 100 MHz to pick some number), shouldn't it just pick up whatever is transmitted at 100 MHz? If you modulate the frequency you are transmitting with, why do I not only pick up, essentially, the equivalent of an AM signal at 100 MHz, instead of picking up on frequencies that are not 100 MHz (Since they've been Frequency Modulated, they're not 100 MHz, which is what my radio is on).

Now obviously FM radio WORKS, so I must be misunderstanding something - but what?

> Is this question "why does it pick up a band (100MHz to eg. 100MHz+20kHz) rather than a single point frequency?" – pjc50 5 mins ago

Yes, that is a fair rephrasing. In my head, an antenna is built + filtered for one frequency. If it's picking up stuff at other frequencies, that's unpredictable and definitely not a way to transfer a signal - yet clearly I'm wrong. How?