We present experimental data on a one-dimensional superconducting metamaterial that is tunable over a broad frequency band. The basic building block of this magnetic thin-film medium is a single-junction (rf-) superconducting quantum interference device (SQUID). Due to the nonlinear inductance of such an element, its resonance frequency is tunable in situ by applying a dc magnetic field. We demonstrate that this results in tunable effective parameters of our metamaterial consisting of 54 SQUIDs. In order to obtain the effective magnetic permeability from the measured data, we employ a technique that uses only the complex transmission coefficient S21.