Jenkins Mechanical Scanning Tabletop Radiovisor Television Receiver RK-1 Kit, circa 1931

Television innovator Charles Frances Jenkins developed mechanical television projectors and receivers like this one as early as the 1920s. Mechanical television works by scanning images with a spinning disk and sending the data via radio waves; the spinning disks of the projectors and receivers must be synchronized. This kit receiver was marketed to radio amateurs; at its height, Jenkins' station in Washington DC broadcasted to several hundred "radiovisor" owners.