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Fine Frequency, Coarse Time Resolution Spectrum Analysis

NSSDCA ID: 1974-097A-05

Mission Name: Helios-A
Principal Investigator:Prof. Donald A. Gurnett


This experiment (E5b) shared the 32-m, tip-to-tip, electric dipole antenna with experiments -04 and -06. Instrumentation consisted of three tunable plasma wave receivers, a fixed-frequency wideband receiver, and a waveform sampler. The tunable receivers and wideband receiver provided data for direct telemetry to earth. Each of the tunable receivers covered a different frequency band in the range 1 Hz to 200 kHz. The high-frequency receiver had 96 frequency settings separated by about 4%, and covered the frequency range 6.4 kHz to 205 kHz. The mid-range receiver had 48 frequency settings separated by about 8%, and covered the range 208 Hz to 6.07 kHz. The low-frequency receiver had 24 settings with 15% separation, and covered the range 11 Hz to 309 Hz. The response time of the low-frequency receiver was approximately 1 s, necessitating the inclusion of the wideband receiver to obtain information about the angular distribution of waves appearing in the low-frequency band. This receiver covered the frequency range 1 Hz to 200 Hz. The time resolution depended in detail on the spacecraft telemetry format, bit rate, and experiment operational mode. When the shock alarm mode became activated, data from the waveform sampler were read into spacecraft memory for a period starting before and ending after the triggering event. In this mode, the instantaneous voltage across the antenna was passed through a low-pass filter with corner frequency dependent on the sampling rate, and measured at discrete intervals, the most rapid being 2.2 ms. One half of the electric dipole failed to deploy properly, and became short-circuited to the spacecraft ground. The resulting configuration was that of a monopole with an operational effective length of about 8 m. This resulted in a 6-dB loss in sensitivity, and an increased receiver noise level, particularly at low frequencies. In addition, the high-gain telemetry antenna produced additional interference. For a more detailed discussion, see p. 248 of Raumfahrtforschung, v. 19, n. 5, 1975.

Alternate Names

  • Helios-A/FineFrequency,CoarseTimeResolutionSpectrumAnalysis
  • Solar Wind Plasma and Radio Wave

Funding Agency

  • NASA-Office of Space Science Applications (United States)


  • Space Physics: Heliospheric Studies

Additional Information

Questions and comments about this experiment can be directed to: Dr. H. Kent Hills



NameRoleOriginal AffiliationE-mail
Dr. Robert G. StoneOther InvestigatorNASA Goddard Space Flight
Dr. Paul J. KelloggOther InvestigatorUniversity of
Dr. Siegfried J. BauerOther InvestigatorUniversitat Graz, Austria
Prof. Donald A. GurnettPrincipal InvestigatorUniversity of Iowa
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