TLDR; The wave file contains APRS data in AX.25 protocol. Decode using DireWolf and plot the resulting GPS coordinates to get the flag.
https://meashiri.github.io/ctf-writeups/posts/202306-dantectf/#almost-perfect-remote-signing

Original writeup (https://meashiri.github.io/ctf-writeups/posts/202306-dantectf/#almost-perfect-remote-signing).