Transponder (for use with Trisponders). Top of object painted silver, bottom of object painted blue. At the side of the object top is a round plastic screw cap and square plastic socket cover which protects the rectangular entry of a 1 pin cable socket.

The basic trisponder system is composed of a distance measuring unit , a master station and two remote stations. Each station is a combined transmitter and receiver. The master station has an omnidirectional antenna, and each remote station has a directional antenna. With the remote unite places over stations of known geographic positions, ranges are observed at the distance measuring unit. These values may be plotted manually on a hydrographic survey sheet or converted by trilateration methods to position values.