Which of the following is required in the identification transmissions from a balloon-borne telemetry station?

Per FCC Part 97 rules for amateur radio, all stations must transmit their assigned call sign for identification purposes. This applies equally to balloon-borne telemetry stations, which are not exempt from basic station identification requirements. While additional information like grid locators, altitude, or transmitter power might be incredibly useful for telemetry tracking and is often transmitted voluntarily by balloon operators, only the call sign is legally required by the FCC for station identification.