The coupler/Antenna tuner has a bunch of high voltage capacitors and inductors (coils of wire) and s couple of stepper motors. The magic internals get the motors to move wiper arms around until the apparent impedance of the antenna measures up correctly..
I once found the feed wire on a huey had broken off inside the tail boom and had a length of about 8 inches, but the HF worked perfectly. The break was repaired, and the HF went back to its usual crap performance....
