天文学百科 The Astronomy Book (Big Ideas Simply Explained)
In the high frequency radio, microwave band, this 1420 MHz radiation is emitted when protons and electrons within a hydrogen atom change their energy state.
However, since we want to get, for example, a 2.4 GHz signal, which is 150 times that of the 16 MHz crystal oscillator, We add a frequency divider into the feedback loop.