We have developed a miniature radio receiver designed to operate as a relative ionospheric opacity meter (riometer). This project was funded by NASA as an enabling technology for future planetary radio science missions. We sought to reduce the instrument's size, mass, and power so that it would be practical for a Mars lander or rover mission. A recent study by our group indicates that a riometer might work well on Mars and offers a potentially rich science return. The technology also has immediate terrestrial applications. For example, the University of Maryland operates a chain of imaging riometers at the Automatic Geophysical Observatories (AGOs) in Antarctica. Our riometer includes features that are desirable for extended autonomous operation such as those with AGOs: low power consumption, wide dynamic range and linearity, computer command and data interface, and the ability to be remotely reconfigured. The receiver design provides significant improvements over previous implementations used in riometers. The high degree of system linearity, combined with a digital feedback loop (including a low-duty calibration cycle), allows more time for viewing the radio sky. We implemented several of the receiver subsystems in a field-programmable gate array, including the receiver detector, the control logic, and the data acquisition and processing blocks. Considerable efforts were made to eliminate or minimize RF noise and spurious emissions generated by the receiver's digital circuitry. Results of laboratory and field tests are presented and discussed.
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