This investigation provided continuous, sheath-independent measurements of the electron density profiles at Jupiter and Saturn and will provide similar measurements for Uranus and Neptune. It also gave basic information on local wave-particle interactions required to carry out comparative studies of the physics of the magnetospheres of these planets. The instrumentation consisted of a 16-channel step frequency receiver and a low-frequency waveform receiver with associated electronics. The frequency range for this instrument was from 10 Hz to 56 kHz. This instrument shared the 10-m antennas developed for the planetary radio astronomy investigation.