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<title>Adjacent-Channel Interference</title> Adjacent-Channel Interference
There isn't a distance requirement, there's a population impacted requirement, which makes it hard to generalize.
Essentially, a typical receiver looking for station A can decode that signal even if station B is about 30 dB (give or take, depending on the specific receiver) stronger on the adjacent channel. So the analysis the FCC does checks how many people who can receive station A would end up with a signal from station B that is 26 or 28 dB (depending on lower or upper adjacent) stronger than station A. If that number is more than 0.5% of the existing interference-free population (or 2% for an LPTV), then the application is not acceptable. Of course, stations can negotiate to accept interference beyond those thresholds, but they can also decline to do so and the 0.5% limit holds.