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VLF Noise and Propagation

NSSDCA ID: 1967-073A-02

Mission Name: OGO 4
Principal Investigator:Prof. Robert A. Helliwell


This experiment consisted of six VLF radio receivers that studied natural and man-made VLF noise occurrences at orbital altitudes. The receiver systems consisted of an inflatable 2.9-m loop antenna, a preamplifier stage at the end of a long boom, and a receiver electronics package in the main body of the satellite. Three step-frequency receivers covering frequency ranges from 0.2 to 1.6, 1.6 to 12.5, and 12.5 to 100 kHz each observed a complete spectrum of 256 signal strength values once every 4.6, 18.4, or 73.7 s, depending on the selected mode of operation. Observations from these receivers were tape recorded at 1 kbs or observed in real time at 4, 16, or 64 kbs. The tape was read out at 64 kbs upon command. These three sweeping receivers could be tuned, on command, to any fixed frequency in their range. The fourth (phase-tracking) receiver operated between 14.4 and 26.3 kHz and was tuned on command to receive signals from any VLF station transmitting in this range. Signal phase and amplitude were observed twice in each commutator frame, making available 512 observations of phase and amplitude every 4.6, 18.4, or 73.7 s, depending on the mode of operation. These data were recorded and transmitted in the same way as the step-frequency receiver data. The fifth and sixth receivers were broadband, operating from 0.015 to 0.30 kHz (ELF) and from 0.30 to 12.5 kHz (VLF). These data were not tape recorded, but were observed only in real time on the special purpose telemetry channel. A matching transformer connected on command to the antenna allowed either electric field or magnetic field observations. This experiment was the same as that for OGO 2, except for the addition of the ELF receiver and the ability to make electric field observations. The experiment operated nominally through February 1968, when the electric field observing mode failed. Subsequent operation continued until spacecraft shutdown in November 1969. The experiment was reactivated in 1970 (February 1 to March 9), and twice in 1971 (January 27 to February 2, and August 17 to September 27). It was turned on once in 1971 for Apollo support, and once to obtain correlative data for USAF Cannonball (71-067C) observations.

Alternate Names

  • OGO4/VLFNoiseandPropagation


  • Space Physics: Ionospheric Studies
  • Space Physics: Magnetospheric Studies

Additional Information

Questions and comments about this experiment can be directed to: Coordinated Request and User Support Office



NameRoleOriginal AffiliationE-mail
Mr. L. H. RordenOther InvestigatorDEVLCO Incorporated
Prof. Robert A. HelliwellPrincipal InvestigatorStanford
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