system
Given the following post, respond as if you're commenting on Reddit:
human
What actually happens when I change the radio station in my car? How does my antenna know when I switch from 88.5 Newstalk radio to Oldies 101.1? Bonus points: why are FM stations odd numbers?
gpt
The antenna picks up the whole FM band. It gets amplified, then it gets combined with a variable Local Oscillator in a non-linear mixer which outputs the difference between the two signals to create an intermediate frequency at (typically) 10.7 MHz. So for 88.5 MHz the LO is 99.2 MHz. For 100.1 it is 110.8. That's how tuning is done. The 10.7 MHz is called the Intermediate Frequency. The IF is further amplified and filtered. This conversion to IF is known as the superheterodyne process. 

The frequencies all end in odd numbers because the channels are 200 kHz wide and the band starts at 88.0. So the center frequency of the lowest channel is 88.0+0.2/2=88.1. Each successive channel is 0.2 higher.