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\~ ,/ <br />______=_~=__<x_, _____ ______ <br />Figure 1. Radio signals from a transmitter, passing through the air water <br />interface. <br />with the apparent sicnal source being a circie on the surface of the water <br />(Priede 1980). The size of the signal source could be calculated by <br />trigonometry, but is obviously small, particularly in shallow water. It is <br />this small circle that is located by radiotrackers and provides the location <br />for taking habitat measurements. As indicated in Figure 1, only a small <br />portion of this radiated power actually crosses the air-water interface and is <br />available to the receiving system. however, if any "significant" energy <br />breaks through the interface, radio reception can occur at long ranges because <br />of the rapid propagation of radio waves in air (Stasko and Pincock 1977). <br />Radiotelemetry in high conductivity waters of 400 ymho or more is marginal <br />(Sinning 1979; Winters 1983), and efforts must be taken to maximize the <br />139 <br />