The decision to sell frequencies as close as 220 MHz away from lower end of radar altimeter band came only in 2019, and aviation world already been working on p

The decision to sell frequencies as close as 220 MHz away from lower end of radar altimeter band came only in 2019, and aviation world already been working on possible interference at the time - which led to much higher guard bands everywhere else and/or extra requirements on use of 3.8-4.0GHz allocations, especially in terms of usage near airports. The issue is that the FCC sale of frequency spectrum up to 3.98GHz doesn't have such limitations, so essentially in 2019 aviation got an unique problem of extra heavy interference in USA