UNCLASSIFIED/UNLIMITED A Digital Radio Receiver for Ionospheric Research

Compared with the experience of the past few decades, ionospheric research in the near future will depend less on new science-dedicated orbital platforms and more on networks of ground facilities. An important role of scientific spacecraft in this context will be to provide space perspectives, as part of space-ground coordinated studies. The enhanced Polar Outflow Probe (ePOP) instrument suite will be launched on the Canadian CASSIOPE spacecraft in early 2008 for space-ground coordinated research. This low-earth-orbit payload will include three instruments for radio-scientific investigation of the ionosphere. One of the radio instruments is a four-channel digital Radio Receiver Instrument (RRI). RRI will be fed by four 3-metre monopoles, arranged in a crossed configuration, each connected to a high-input impedance preamplifier. The RRI bandwidth will extend from 10 Hz to 18 MHz. RRI will measure the electric fields of either spontaneous waves or waves created by ground transmitters, such as ionosondes, high-frequency radars and ionospheric heaters. A review of the design features of the RRI reflects the observational requirements. Accurate measurements of the intensity, frequency, direction of propagation, and signal delay of such fields over the broad frequency range will be accomplished using modern digital receiver techniques. The amplified signals from the monopoles will be digitized at a rate of 40 megasamples per second, and from there, the signal will be down-converted, filtered, time-stamped, and communicated purely in digital form. The major features of the RRI are described in the light of the measurement goals that inspired them. Results of recent end-to-end tests of the RRI protoflight model are followed by an outline of the operating modes of the instrument. 1