A new system has been installed on the JET tokamak consisting of 6 independent fast-sweeping reflectometers, covering 4 bands between 44 and 150GHz and using orthogonal polarisations. It has been designed to measure density profiles from the plasma edge to the centre, launching microwaves through 40m of over-sized corrugated waveguides. It has routinely produced density profiles with a maximum repetition rate of one profile every 15s and up to 100,000 profiles per pulse.