It's an incredible feat to me that a single station can broadcast to the almost the entire US, Mexico, and even parts of South America at the right time of day [0]. (I believe this is why many clocks check for the signal overnight.) It's achieved by using an extremely low frequency, at 60 kHz. The antenna is enormous and suspended between 4 towers.

[0] https://tf.nist.gov/stations/wwvbcoverage.htm

[1] https://www.nist.gov/pml/time-and-frequency-division/time-di...