As radio prospered throughout the 1920s and 1930s, experimental television stations, which broadcast both an audio and a video signal, began sporadic broadcasts. Licenses for these experimental stations were often granted to experienced radio broadcasters, and thus advances in television technology closely followed breakthroughs in radio technology. As interest in television grew, and as early television stations began regular broadcasts, the idea of networking television signals (sending one station's video and audio signal to outlying stations) was born. However, the signal from an electronic television system, containing much more information than a radio signal, required a broadband transmission medium. Transmission by a nationwide series of radio relay towers would be possible but extremely expensive.