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General comments… There are dozens of licensed AM broadcast stations operating on 1600 kHz just in the eastern US. Their skywave signals at night can extend for hundreds of miles. At distant receive sites normally they combine to make none of them intelligible/usable. But their combined field strength there would still interfere with the signal of a Part 15 AM setup, except close to its antenna.
An AM signal needs to be quite a bit stronger than whatever else is on the channel in order to be heard without a lot of interference. So at 1.8 miles, where your Part 15 signal is very weak, it won’t take much nighttime skywave from other stations to interfere with it.