About one mile away is a 5 kw AM tower, daytime only, at 850 KHz. Unlike all other local daytimers, it goes off 1-hour after local sundown, which is sundown Denver time, where the station being protected is 50 kw KOA.
By chance this one station at 850 KHz produces “interference which must be acctepted,” according to the rules, by putting an intense RFI (radio frequency interference) on the phone line, also the DSL line, and a buzzing second harmonic at 1700 KHz. Except for that, 1700 KHz is very clear here, so I use it at night starting one hour after sundown. During the day I use 1680 KHz, the next closest clear spot.
This frequency jumping is a reminder of the way international shortwave stations switch frequencies at different times, but there reason is to reach certain land masses during particular hours.