A new type of radio spectrograph is described here which has been used to observe the interplanetary scintillation of a radio source over a two-to-one frequency range. Simultaneous observations over this range provide a direct insight into the time variations of intensity and the physical form of the interplanetary irregularities producing them. A specific example shows the direct way in which the spectral record can indicate the physical details of the electron density variations of the interplanetary medium.