1680 is at the far upper end of the AM band called The Expanded Band. The propagation characteristics of the higher end of the MW band essentially doesn't carry as far, where the lower end (570kHz) is much more conducive to receiving a signal farther away from the transmission point. The way a signal at a certain wavelength interacts with the ionosphere determines how far the signal propagates. Lower frequencies are longer wavelengths and are preferable to shorter wavelengths at higher frequencies.How so? How could it be any different anywhere else on the band? Their 1680 signal is pretty strong throughout the metro, day and night, especially in South King County, where probably the majority of Latinos live.
The FCC added the expanded band in 1983, so radios manufactured prior to then didn't even have that end of the band available.
The high end of the band is also plagued with more terrestrial noise than lower.
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