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EXAMPLES OF TRANSMISSION SYSTEMS 25Support structures. The remote station equipment other thon sensors andantennae is enclosed in weatherproof metal boxes, which are presently mounted at thebases of the most resilient, unguyed, ground-rooted towers we were able to supply athand-toPPed-and unlimbed trees. The above snow sensors and the radio antenna aremounted above the maximum expected snow level.Two coi1CejJf:s here are 'worthy of note. _. 'Firstly, the- placing of equipment onor even in the ground reduces tower loading and the snow cover provides good protectionfrom the environment. Secondly, while our use of trees os towers is notnecessarily advocated for long-term application, we feel that permonent structuresshould be designed with parollel characteristics and performance.Sensors and encoders. While the raingauge and snow pillow have been retoin~ed from earlier models, the thermistor and its onalogue-to-digital encoder, and thepressure detector and encoder for the snow pillow are new designs and show greatpromise.The temperature encoder is a simple electronic device. for digitizing ofresistance and appears to be reliable. Accuracy and linearity of this unit will beimproved before inclusion in the final system.The snow pillow pressure digitizing encoder in this model is very good. Thedesign is essentially based on that of an open mercury manometer, employing a servodrivenmicrometer lead screw to detect mercury level.Programmer control. The readout of sensors, digitizing and scanning of dataand format of sequential transmission of information is directly controlled or accomplishedby a solid state programmer, the design of which is based on digital computerlogic functions.Power supply. Alkaline "dry" electrolyte primary cells make up the batteryused to supply the remote station. These batteries are efficient at low temperatures,and are capable of operating the system for up to two years, depending on the frequencyof reports and the number of batteries used.Recording. An automatic electric typewriter equipped for computer-typedata input is employed at the base station to record both telemetered data and date/time information provided locally. The design of the telemetry link/recorder interfaceequipment is based on the same logic functions as the remote station programmer,and effectively reverses the role of that equipment by converting the sequentialbinary-coded-decimal transmission of data into parallel output for the typewriter.Results. Outside of one period when records were interrupted by failure ofthe printer input power supply at the base station, operation of the system has beenvery satisfactory. The remote station did fail to transmit data for one two-dayperiod, but it was found that the ambient temperature had dropped below the designoperating minimum of _30 0 Fahrenheit. As soon as the temperature rose above thatpoint, normal operation was resumed automatically.From our point of view, however, the most encouraging feature of theis the proving of the inherent reliability of the remote station equipment.systemAt the