| DESCRIPTION |
INSTRUMENT: PLASMA WAVE RECEIVER
SPACECRAFT: VOYAGER 1
Instrument Overview
===================
Instrument Id : PWS
Instrument Host Id : VG1
Principal Investigator : DONALD A. GURNETT
PI PDS User Id : DGURNETT
Instrument Name : PLASMA WAVE RECEIVER
Instrument Type : PLASMA WAVE SPECTROMETER
Build Date : UNK
Instrument Mass : 1.400000
Instrument Length : 0.318000
Instrument Width : 0.185000
Instrument Height : 0.048000
Instrument Serial Number : SN002
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, the number of frames obtained was
very small due to the lower telemetry rates available at the
greater distance of that planet.
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 and Saturn. 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.
'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.
Electronics
===========
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
digitization.
Section 'SA'
------------
Total Fovs : 1
Data Rate : 32.000000
Sample Bits : 8
'SA' Detectors
--------------
PWS ANTENNAS
'SA' Section FOV Shape 'DIPOLE'
-------------------------------
Section Id : SA
Fovs : 1
Horizontal Fov : 360.000000
Vertical Fov : 180.000000
'SA' Section Parameter 'WAVE ELECTRIC FIELD INTENSITY'
------------------------------------------------------
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
----------------
PWS ANTENNA
'WFRM' Section FOV Shape 'DIPOLE'
---------------------------------
Section Id : WFRM
Fovs : 1
Horizontal Fov : 360.000000
Vertical Fov : 180.000000
'WFRM' Section Parameter 'ELECTRIC FIELD COMPONENT'
---------------------------------------------------
A measured parameter equaling the electric field strength
(e.g. in milli-Volts per meter) along a particular axis
direction.
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.
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