i:0:"i/8.in"
p:,/{+x@&~=#x}'x@=i./:x:+&"."<i  / all pairs of antennae with the same frequency
t:{-1_(~^i.)+[x-y;]\x}.'p        / list of antinodes produced by each pair
+/~^*'?*'1_'t                    / part 1: number of unique "first" antinodes
#?,/t                            / part 2: number of unique antinodes

Today, part 1 was a bit annoying: I have to get the second element of each antinode list. If the list only has one element, nulls start showing up, and the code to handle them gets clumsy. Though, I should be thankful that all antennae of the same frequency are coprime!

~/aoc24k/8.html