Telemetering data from electronic devices that sense ground tilt, temperature, strain, gas concentration, and other phenomena can provide valuable information regarding current or impending volcanic activity. To facilitate such monitoring, I developed a low-data-rate digital telemetry system that transmits data at 10-minute intervals over VHF/UHF radio links to a central receiving site. Analog voltages are digitized with a 12-bit-plus-sign analog-to-digital converter in the field. The data are transmitted in Bell 103 format so that most computers with a Bell 103 compatible modem attached to their serial port can receive, process, and store the data. A 9-gallon steel drum houses the entire transmitter including radio, antenna, and sufficient batteries to power the unit for a year. Design considerations imposed by Mount St. Helens resulted in a robust, low-cost, low-power system with wide applicability at other volcanoes.
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