A practical look at antenna and propagation requirements in biotelemetry systems for fresh water fish

Propagation from a transmitter/antenna implanted in a fresh water fish is discussed. The choice of operating frequency based upon fish size, antenna efficiency and refraction effects is presented. The implanted linear antenna is placed laterally along the fish. It is shown that for parallel polarization (E in the plane of incidence) the wave, in air, has polarization dependent upon the elevation angle of the receiving antenna. For perpendicular polarization the polarization of the wave is always horizontal. Hence the polarization of the signal in the air depends upon the fishes position in the water. This leads to the conclusion that ground based receiving antennas should be circularly polarized so that either case can be handled. For air-borne tracking, the major cone of reception places the aircraft at higher elevation angles and hence requires a horizontally polarized antenna. Since the fish can be at various azimuthal angles, a circularly polarized antenna placed beneath the aircraft is dictated. The paper concludes with a discussion of an actual operating system as used by the U.S. Fish and Wildlife Service on the Truckee River.