VLF/ELF Multichannel Receiver

A new multichannel receiver - VELOX (VLF/ELF Logger Experiment) - deployed at Halley in January 1992, superseded both the multichannel system described by Smith and Yearby (1987), which formed part of the Mk-1 AVDAS, and the VLF/ELF channels of the Real-time Antarctic Logger Facility (RALF) system (Gough et al., 1987). The frequency bands covered by the VELOX are shown in the Table. The selections have been designed to be as similar as possible to the multichannel receivers previously operated at Halley, and with certain other receivers which operate or are planned to operate in Antarctica. The latter include the Stanford University ULF/ELF/VLF Radiometer (Fraser-Smith and Helliwell, 1985) and the US AGO (`PENGUIN') VLF receiver (Inan, private communication, 1989).

For channels 1-9, each of the broadband preamplifier outputs is anti-alias filtered, and digitised to 12 bits at a 512 kHz rate. Filtering into the selected bands is achieved digitally. For channel 10, a separate tunable receiver is provided (not implemented at the time of writing). Automatic gain control is used to achieve an overall dynamic range of 90 dB.

Scalar power (P) and vector power (Px, Py, Pz), averaged over each of the frequency bands, are computed at intervals of 10 ms, using the complex Fourier transforms of the signals received by the loop aerials (proportional to the east-west and north-south components respectively, of the horizontal wave magnetic field).

In each recording interval (programmable in the range 1-60 s, but normally 1 s), the parameters defined below are computed.

More information and data.

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