Radio uses electromagnetic waves to transmit signals by modulating properties like amplitude, frequency, or phase. When radio waves interact with an electrical conductor, it induces an alternating current that can be transformed into sounds or signals carrying information. Home recording of radio programs became more common in the 1950s as affordable reel-to-reel tape recorders were introduced, allowing people to record broadcasts. In the early days of radio, most programs were presented live since networks originally prohibited recorded content until the late 1940s, requiring some shows to be performed multiple times for different time zones.