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| Titel |
Interpretation of Cluster WBD frequency conversion mode data |
| VerfasserIn |
J. S. Pickett, I. W. Christopher, D. L. Kirchner |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
2193-0856
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Instrumentation, Methods and Data Systems ; 3, no. 1 ; Nr. 3, no. 1 (2014-02-13), S.21-27 |
| Datensatznummer |
250115209
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| Publikation (Nr.) |
 copernicus.org/gi-3-21-2014.pdf |
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| Zusammenfassung |
| The Cluster wide-band data (WBD) plasma wave receiver mounted on each of the
four Cluster spacecraft obtains high time resolution waveform data in the
frequency range of ~70 Hz to 577 kHz. In order to make measurements
above 77 kHz, it uses frequency conversion to sample the higher frequency
waves at one of three different conversion frequencies (~125, 250 and
500 kHz, these frequencies being the possible options for setting the base
frequency of the frequency range being sampled) in one of three different
filter bandwidths (9.5, 19 and 77 kHz). Within the WBD instrument, a
down-conversion technique, built around quadrature mixing, is used to convert
these data to baseband (0 kHz) in order to reduce the sample rate for
telemetry to the ground. We describe this down-conversion technique and
illustrate it through data obtained in space. Because these down-converted
data sometimes contain pulses, which can be indicative of nonlinear physical
structures (e.g., electron phase-space holes and electron density
enhancements and depletions), it is necessary to understand what effects
mixing and down conversion have on them. We present simulations using
constructed signals containing pulses, nonlinear wave packets, sinusoids and
noise. We show that the pulses and impulsive wave packets, if of sufficient
amplitude and of appropriate width, survive the down-conversion process,
sometimes with the same pulse shape but usually with reduced amplitude, and
have timescales consistent with the filter bandwidth at the base frequency.
Although we cannot infer the actual timescale of the pulses and impulsive
wave packets as originally recorded by the WBD instrument before mixing and
down conversion, their presence indicates nonlinear processes occurring at or
somewhat near the location of the measurement. Sinusoidal waves are
represented in the down-conversion timescale as sinusoids of nearly the same
amplitude and at frequencies adjusted down by the conversion frequency. The
original input waveforms, regardless of their shape, whether pulses or
sinusoids, can never be recovered from the down-converted waveforms. |
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