The Design and Use of an FM / AM Radiotelemetry System for Multichannel Recording of Biological Data

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Abstract
A multichannel telemetry system for EEG recording has been constructed for study of animal or human behavior correlates under natural, unrestrained conditions. To be useful in research of this kind, the transmitted radio signal must be independent of the environment, so that changes in antenna loading and in signal level cause no artifact. Standard IRIG proportional-bandwidth FM subcarrier channels are used. These subcarriers are generated by twin-T oscillators, modulated in turn by the amplified data signals. The FM subcarriers are then linearly summed and impressed upon a crystal-controlled AM transmitter. The system is also relatively insensitive to major shifts in supply voltage. Wherever possible, fabrication was by means of integrated circuits, thus reducing the bulk of the modules.