Instrument Overview
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      Fluctuating electric fields are detected in three
      pairs of orthogonal antennas, one aligned with the
      spacecraft spin axis and the other two in the
      equatorial plane (Fig. 6).  The antenna voltages
      are preamplified and then analyzed by a radiometer
      consisting of four superheterodyne receivers, which
      step through the frequency range from 30 kHz to 2
      MHz.  Two channels are narrow-band with a filter
      bandwidth of 3 kHz, and two have a filter bandwidth
      of 10 kHz.  The narrow-band filters sweep between
      30 kHz and 1 MHz in 12 steps, while the broadband
      filters cover frequencies between 40 kHz and 2 MHz,
      also in 12 steps.  The frequencies are scanned in a
      nonlinear manner so that the highest frequencies
      are sampled 12 times as often as the low
      frequencies.  The complete scan sequence consists
      of 72 steps; 56 s are required to read out all
      channels at 1024 bit/s.