Quantifying reception strength and omnidirectionality of underwater radio telemetry antennas: Advances and applications for fisheries research

Radio telemetry is used in many freshwater fisheries applications as a tool to study fish behavior; however, the limited ability of radio signals to travel through the water (up to 15 m) limits the ability to detect fish located in deep-water habitats with conventional aerial antennas. Underwater radio antennas are seldom used in aquatic research relative to aerial applications, but are very useful in detecting organisms at depth. To add to this knowledge base, we report on the reception characteristics of two types of underwater radio antennas relatively new to the fisheries field, the turnstile and balanced loop-vee antennas, and compare these to an underwater dipole antenna, which has been more commonly used for fisheries research compared to the formerly mentioned antennas. Reception strength and omnidirectionality of the three antenna types were tested in the laboratory. Maximum detection range of antennas was also quantified in the field using a commonly employed radio telemetry system. Results indicate that the balanced loop-vee antenna had stronger overall reception strength (-36.84 dBm) than either the turnstile (-43.72 dBm) or dipole (-43.72 dBm) antennas; the balanced loop-vee was also the most omnidirectional (i.e., lowest variance, SD=0.42) of the three armored underwater antenna types. Further, the XY plane of the balanced loop-vee had stronger reception strength (-32.71 dBm) than all other plane/antenna combinations. Field testing results confirmed that the balanced loop-vee antenna had the strongest reception strength of all antenna types and detected radio transmitters as far as 15 m through water. The dipole and turnstile antennas were able to detect transmitters as far as 9 m and 12 m through water, respectively. The reception characteristics of the balanced loop-vee antenna demonstrate its usefulness as a tool for aquatic telemetry research. (C) 2012 Elsevier B.V. All rights reserved.