Transponder (for use with Trisponders). Top of object painted grey, bottom of object painted blue. At the side of the object top is a rectangular entry of a 1 pin cable socket, with plastic screw cap missing and next to it is an additional round cable entry for a 1 pin plug. The other side of the transponder has a pin socket out.

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.