U.S. Department of Agriculture: Animal and Plant Health Inspection Service


Date of this Version

August 2006




We evaluated the effectiveness of receiver/data loggers for monitoring the presence/absence of radiocollared animals in discrete areas. Our primary objective was to determine how variation in transmitter signal strength affected the size of area being monitored. This information will help researchers better manage the uncertainty related to determining an animal’s location relative to a discrete boundary. We used an adjustable attenuator to measure signal strength to determine the minimum number of decibels (dB) required to eliminate detection of a radio signal by receiver/data loggers. We quantified how dB varied depending upon orientation of the transmitter on the animal and distance from receiver/data logger (radius of detection). Based upon this signal strength variation, we then calculated a zone of uncertainty (i.e., the area in which detection of a radio signal was uncertain at a particular radius of detection). The zone of uncertainty increased exponentially with a linear increase in radius of detection. We do not recommend using receiver/data loggers to monitor radiocollared animals in discrete areas unless uncertainty is acceptable.