*Question E1D04:
[97.119(a)] Which of the following is required in the identification transmissions from a balloon-borne telemetry station?*  

*Correct Answer is  A: Call sign*  

### AI Response: (may contain errors)  

In the context of amateur radio, identification is crucial for ensuring that transmissions can be traced back to the responsible operator. According to FCC regulations, specifically [97.119(a)], the primary requirement for identification is the transmission of the station's call sign.

### Explanation:

1. **Correct Answer: Call sign (A)**
   - **Why it's correct:** The FCC mandates that all amateur radio stations, including balloon-borne telemetry stations, must identify themselves by transmitting their call sign. This is the primary method of identification and is required to ensure accountability and traceability of transmissions.

2. **Why the other choices are incorrect:**
   - **B: The output power of the balloon transmitter**
     - While knowing the output power might be useful for operational purposes, it is not required for identification purposes. The FCC does not mandate the transmission of power levels as part of the identification process.
   - **C: The station's six-character Maidenhead grid locator**
     - The Maidenhead grid locator is a system used to specify locations, but it is not required for identification. It is often used in contests and for logging purposes, but not for regulatory identification.
   - **D: All these choices are correct**
     - Since only the call sign is required for identification, this option is incorrect. The other elements (output power and grid locator) are not mandated by the FCC for identification purposes.

### Key Rule:
- **FCC Rule [97.119(a)]:** This rule specifies that the call sign must be transmitted to identify the station. It is the only required element for identification in this context.

By focusing on the call sign, operators ensure compliance with FCC regulations and maintain proper identification of their transmissions.