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Instrument Information

  Instrument Overview
    Instrument Id                  : PWS
    Instrument Host Id             : VG2
    Principal Investigator         : DONALD A. GURNETT
    PI PDS User Id                 : DGURNETT
    Instrument Name                : PLASMA WAVE RECEIVER
    Instrument Type                : PLASMA WAVE SPECTROMETER
    Build Date                     : 1976-11-28
    Instrument Mass                : 1.400000
    Instrument Length              : 0.318000
    Instrument Width               : 0.185000
    Instrument Height              : 0.048000
    Instrument Serial Number       : SN003
    Instrument Manufacturer Name   : THE UNIVERSITY OF IOWA
    The Plasma Wave Receiver on Voyager consists of both a
    16-channel spectrum analyzer covering the range of 10 Hertz to
    56.2 kiloHertz and a wideband waveform receiver which returns
    the waveform of waves in the frequency range of 40 Hertz to 12
    kiloHertz.  The spectrum analyzer provides data on a continual
    basis with a maximum temporal resolution of one spectrum per 4
    seconds.  The waveform receiver returns 4-bit samples of the
    electric field measured at a rate of 28,800 samples per second.
    Because of the very high data rate, the waveform samples must
    be transmitted in the same manner as the Voyager imaging
    information.  At Jupiter, some 10,000 48-second waveform frames
    were obtained.  At Saturn, Uranus, and Neptune, the number of
    frames obtained was very small due to the lower telemetry rates
    available at the greater distances of those planets.
  Science Objectives
    The primary science objective of the Voyager plasma wave
    investigation is to make the first surveys of the plasma wave
    and low frequency radio wave spectra in the magnetospheres of
    the outer planets: Jupiter, Saturn, Uranus, and Neptune.
    Plasma waves participate in a fundamental manner in the
    dynamics of planetary magnetospheres and in the interactions of
    that magnetosphere with the external solar wind and internal
    perturbations such as those induced by satellites interior to
    the magnetosphere.  Plasma waves also provide diagnostic
    information about the plasma environment near the planets
    including such parameters as electron density and sometimes
    temperature.  The instrument is also sensitive to low frequency
    radio emissions and, therefore, acts as a low frequency
    extension to the Planetary Radio Astronomy investigation.
    Radio waves are often the only means of remotely observing
    regions of plasma not accessible to the spacecraft and also
    lead to remote diagnostics of plasma conditions.  The plasma
    wave receivers are also sensitive to the results of small dust
    particles impacting on various parts of the spacecraft at high
    velocities and, hence, provide a direct measure of the rate of
    impact, the density of the dust, and an estimate of the mass
    distribution of dust in the vicinity of the large planets,
    especially those with rings and otherwise dusty environments.
    Finally, the Plasma Wave Receiver will characterize the plasma
    wave and radio wave spectrum of the outer heliosphere and
    perhaps beyond, extending our understanding of solar wind
    plasma processes and wave-particle interactions to several tens
    of Astronomical Units.
  Operational Considerations
    The primary operational considerations of the PWS include
    maintaining the proper operating mode and obtaining waveform
    samples as often as the spacecraft tape recorder/downlink
    capabilities allow.  The standard instrument mode is with
    Waveform Power On and Input Gain State Hi.  For encounter
    periods, this corresponds to GS3GAINHI/WFMPWRON.  Since there
    has never been a period when the signal levels were so high as
    to require the Low input gain state, and it is highly unlikely
    that such levels will ever be encountered, Low Input Gain State
    should never be selected.  As long as there is power margin
    available, it is most straightforward to leave the Waveform
    Receiver Power on.  The power consumption is less than 0.5 Watt
    for this section, hence, the power savings afforded by turning
    it off is not large.  The most involved operational
    consideration is providing for the transmission of waveform
    data to the ground.  At Jupiter, the majority of the waveform
    data could be sent directly to the ground via the 115200 bps
    downlink.  This capability disappeared after Jupiter, however,
    because of the greater distance to the spacecraft, hence, lower
    telecon rates.  Since operating the A/D converter at a rate
    less than 28800 Hertz would result in aliasing, it is necessary
    to record the data at the 115200 bps rate on the spacecraft
    tape recorder using the appropriate data mode and playback the
    recorded data at a lower rate, commensurate with the link
    capabilities.  Again, a choice of the proper playback mode is
    required.  Since the data modes available on the spacecraft are
    highly dependent on mission phase, these modes are not
    described here.
  Calibration Description
    The Voyager plasma wave receiver spectrum analyzers were
    calibrated by first establishing a relationship between input
    voltage (of a sine wave at the filter center frequency) and
    output voltage and second by measuring the effective bandwidth
    of the filter.  The bandwidth is measured by applying a random
    noise signal of known spectral density and by measuring the
    output voltage which, by the first part of the calibration, is
    related to the rms voltage of a sine wave.  Dividing the
    equivalent sine wave voltage squared by the input spectral
    density gives a bandwidth.  This procedure is repeated for each
    of the frequency channels.  A special calibration problem
    exists for the upper 8 frequency channels (1 kiloHertz and
    above) due to a failure of a 'tree switch' in the Flight Data
    System.  An in-flight recalibration was attempted by using a
    Solar type III radio burst observed by both Voyager 1 and 2.
    The recalibration has known deficiencies, but it has been
    impossible to date to improve on them.  The deficiencies
    include 'flat-topped' emissions where the emission appears to
    grow in amplitude up to some plateau level and then stay
    artificially flat for long periods of time.  The background
    level for each of the channels can vary in step-level fashion
    based on a number of engineering parameters which utilize the
    same failed circuitry.  Other results of the tree-switch
    recalibration is that the instrument sensitivity is decreased
    by some amount which is not well known and the absolute
    calibration could be off as well.  The calibration validity
    could be a function of frequency since some channels' (mostly
    the upper 3 channels, 17.8 kHz and above) calibration has been
    verified with the PRA, but others have not and seem internally
    inconsistent with the lower frequency, unaffected channels.
  'PWS ANTENNA' Detector
    Detector Type                  : DIPOLE ANTENNA
    Nominal Operating Temperature  : 298.000000
    The PWS uses a pair of 10 meter antenna elements as a balanced
    dipole antenna.  The two elements are extended from the
    spacecraft at right angles to each other.  (The elements are
    shared with the Planetary Radio Astronomy instrument, which
    uses them as a pair of monopoles so that measurements of the
    degree of right and left hand circular polarization can be
    made.) The PWS measures the voltage difference between the two
    elements which, when coupled with the effective length of the
    antenna system (7.07 m) yields an electric field strength in
    units of volt/meter.  The antenna system has the usual dipole
    antenna pattern which yields nearly 4*pi steradians in its
    field of view, although there is a range of fields of view
    where the detector response drops dramatically as one expects
    from a dipole pattern.
    The PWS antenna, used as a balanced dipole with an effective
    length of 7.07 meters gives a sensitivity to fluctuating (wave)
    electric fields down to the range of 5.E-6 volt/meter.  Even
    though the antenna elements are extended orthogonally to each
    other, the antenna pattern is still a dipole since the elements
    are short with respect to the wavelengths of the waves.  The
    presence of the various parts of the spacecraft in close
    proximity to the antenna can result in a distorted pattern, but
    this has not been studied in the frequency range of the PWS.
    The PWS electronics system consists of three basic sections.
    The first is the power supply system which regulates and
    filters the 28 volt, 2400 Hertz spacecraft power supply and
    provides DC voltages to the remainder of the instrument
    electronics.  The second section is the spectrum analyzer which
    consists of two banks of 8 narrowband filters, and two
    logarithmic detectors, each of which provides an analog voltage
    proportional to the log of the signal strength delivered to the
    detector from any of the eight filters it services.  The analog
    outputs from these two compressors, as they are called, are
    sent to the Flight Data System of the spacecraft for conversion
    to an 8-bit digital value.  The spacecraft steps the inputs to
    the two compressors periodically (once per 0.5 seconds in GS3
    or encounter mode) so that signal strengths in each of the 16
    channels is measured over a 4-second interval.  The third
    section consists of a single broadband filter of 40 Hertz to 12
    kiloHertz, an automatic gain controlled amplifier, and a 4-bit
    A/D converter.  This section digitizes the electric field
    waveform at a 28800 Hertz rate.  The output amplitude is
    controlled by the automatic gain control in order to keep the
    signals within the useful range provided by the 4-bit
    Section 'SA'
      Total Fovs                     : 1
      Data Rate                      : 32.000000
      Sample Bits                    : 8
    'SA' Detectors
    'SA' Section FOV Shape 'DIPOLE'
      Section Id                     : SA
      Fovs                           : 1
      Horizontal Fov                 : 360.000000
      Vertical Fov                   : 180.000000
      A measured parameter equaling the electric field strength in
      a specific frequency passband (in MKS unit: VOLTS/METER)
      measured in a single sensor or antenna.
      Instrument Parameter Name    : WAVE ELECTRIC FIELD INTENSITY
      Sampling Parameter Name      : TIME
      Instrument Parameter Unit    : VOLT/METER
      Minimum Instrument Parameter : 0.000005
      Maximum Instrument Parameter : 0.500000
      Noise Level                  : 0.000005
      Sampling Parameter Interval  : 4.000000
      Sampling Parameter Resolution: 4.000000
      Sampling Parameter Unit      : SECOND
    Section 'WFRM'
      Total Fovs                     : 1
      Data Rate                      : 115200.000000
      Sample Bits                    : 4
    'WFRM' Detectors
    'WFRM' Section FOV Shape 'DIPOLE'
      Section Id                     : WFRM
      Fovs                           : 1
      Horizontal Fov                 : 360.000000
      Vertical Fov                   : 180.000000
      A measured parameter equaling the electric field strength
      (e.g.  in milli-Volts per meter) along a particular axis
      Instrument Parameter Name    : ELECTRIC FIELD COMPONENT
      Sampling Parameter Name      : TIME
      Instrument Parameter Unit    : VOLT/METER
      Minimum Instrument Parameter : 0.000005
      Maximum Instrument Parameter : 0.500000
      Noise Level                  : 0.000005
      Sampling Parameter Interval  : 0.000035
      Sampling Parameter Resolution: 0.000035
      Sampling Parameter Unit      : SECOND
  Operating Modes 'GS3GAINHI/WFMPWRON'
    Data Path Type                 : REALTIME
    Gain Mode Id                   : HIGH
    Instrument Power Consumption   : 1.600000
    The PWS instrument gain is high and the waveform receiver power
    is on.  This is the normal encounter operating mode of the
    instrument and places it in its most sensitive input gain state
    with the waveform receiver section turned on.  The fact that
    the waveform receiver power is on does not guarantee that
    waveform data is available.  The spacecraft is in the GS-3 data
    mode which cycles the plasma wave spectrum analyzer so that a
    complete spectrum is obtained every 4 seconds.
  Mounted On Platform 'SPACECRAFT BUS'
    Cone Offset Angle              : UNK
    Cross Cone Offset Angle        : UNK
    Twist Offset Angle             : UNK
    The PWS is mounted on top of the Planetary Radio Astronomy
    experiment on top of spacecraft bus bays 8 and 9.  The two
    orthogonal antenna elements are attached to the Planetary radio
    astronomy package.
REFERENCE_DESCRIPTION Scarf, F.L., and D.A. Gurnett, A Plasma Wave Investigation for the VoyagerMission, Space Sci. Rev., Vol. 21, p. 289, 1977.
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