Dating back to the early days of radio in the 1920’s, broadcasters would begin transmissions with a short and distinctive melodic passage followed by an announcement of the station’s name and frequency. These melodic passages came to be known as interval signals and would be played at the top of the hour (and sometimes at half-past the hour). National broadcasters typically excerpted rousing musical phrases from marches, anthems of works of a favorite-son composer.
Through the 1930’s and 40’s, many national broadcasters used shortwave transmitters to reach listeners around the world. As with its domestic service, the national broadcaster would use the interval signal at the beginning of transmissions on its international service. In addition to identifying the broadcaster, the interval signal aided a listener in tuning in to the program.