Today the tuning dial numbers are waves per second. Engineers call this number the frequency. Today's AM broadcast band has the frequencies between 535 kHz and 1610 kHz. The antenna wire picks up the radio wave electricity. A crystal radio needs a long antenna wire.
Big antennas pick up more radio wave electricity.
The antenna wire is just any electric wire that goes from the radio high up in the air. Longer than 80 feet is good. It works better outside and high up. Higher than 20 feet high is good. A good crystal radio antenna can be a small copper wire going out of a window and up high in a tree.