Like the test cards that used to be a familiar sight on TV screens when there was nothing to broadcast, radio interval signals used to fill the airways.

These short musical sequences, a global phenomenon of signals typically played before or during breaks in radio transmission, now fill the air once more – but this time above Oxford.

A sound work using 50 of these musical signatures specially commissioned by Modern Art Oxford from the Berlin-based Susan Philipsz, known for her evocative voice or sound installations, is being transmitted from the gallery’s rooftop across the city to the Radcliffe Observatory at Green Templeton College. This beautiful octagonal tower, built in the late 18th century for viewing the Transit of Venus and modelled on the Tower of the Winds in Athens, is now part surrounded by the rubble of the Radcliffe Infirmary building site. This suits Susan’s concept. She says it makes the tower “look as if it’s landed from outer space!” Asked to create an artwork that responded to the historical site, she thought of deep space, infinity, and the nature of the observatory itself as a metaphorical frontier to the stars. She found out that the radio technology pioneer Guglielmo Marconi suggested that sounds, once generated, never die. Taken with this idea, of sounds fading but continuing as sound waves across the universe, of tuning into the universe, she imagined that in the days when radio interval signals were commonplace “you could be anywhere, in the middle of nowhere, and still tune in”. Hence the title: You are not Alone.

An appealing idea. Standing in the observatory listening to the melodic sequences of chimes from four speakers, the recordings made more haunting by the use of a vibraphone, I imagined the lament making its physical journey as sound waves across the city – sounds with faraway origins filling the air above us.

It’s a wondrous experience – and more so after dark, I’m told. The first of three proposed commissions by MAO for the Radcliffe Observatory, it’s open Tuesday to Sunday between 2pm and 5pm until December 3. Free. No need to book.

Visit www.moder