English: An early mechanical-scan television display device, the Jenkins Radiovisor, from an advertisement in a radio magazine by Jenkins Television Corp., Passaic, New Jersey, in 1931. It was used in experimental television receivers during the 1930s. During the 1920s and 30s dozens of experimental stations broadcast television using this mechanical-scan technology. The radiovisor consists of a metal disk pierced with a spiral pattern of holes, called a Nipkow disk, turned by a synchronous motor. Behind the disk is a neon glow lamp. When the disk is spun by the motor, each hole passing in front of the neon lamp creates a scan line in the image. The radio signal from the television station is picked up by an antenna attached to a vacuum tube receiver unit, producing a video signal which is applied to the neon lamp. The varying signal causes varying light intensity from the lamp, representing the different brightness values of the image. The result is a dim fuzzy monochrome orange picture about 1 1/2 inches (3 cm) square. The viewer looks into the lens (left) which magnifies the image. The most common standard was a 60- line image at a frame rate of 20 frames per second. For this standard there were 60 holes around the disk, each one producing a scan line. The disk made one rotation for each video frame, so it turned at a rate of 1200 RPM. It was sold as a kit for $42.50 with the lens extra.