You can purchase in many radio and electronic hobby shops antenna kits which include the antenna, insulators, lead wire, and lightning arrestor. The ground wire can be attached to a metal cold water pipe, or to a metal rod stuck a couple of feet into the earth. Do not attach it to a line carrying gas or electricity. They are still available through electronics suppliers and some hobby shops. The capacitor The capacitor, or condenser, though not essential for operation of these sets, does help to refine their use when it is added.
More complicated sets have a variable capacitor.
For the simplest sets, however, a fixed capacitor of around .002 mF or so is sufficient. A capacitor is also very simple to build. The Cub Scouts, being the great caretakers of crystal radio lore that they are, included this picture in the 1954 edition of the Wolf Cub Book. It lacked annotation of any kind other than what is here. The most important thing to know is that all of the tinfoil pieces need to be completely insulated from one another.