Which of the following is normally used when sending automatic location reports via amateur radio?

The correct choice is a Global Positioning System (GPS) receiver, as it is specifically designed to determine precise geographical locations using signals from satellites. In the context of amateur radio, GPS receivers can be connected to radios to automatically send location reports, which is especially useful for mobile operators or in situations where tracking the position of a vehicle or portable station is necessary. This automated process enhances communication by providing real-time location data to others who are monitoring the transmission.

The other options may relate to various technologies but do not directly facilitate automatic location reporting in the same way. For instance, connecting to a vehicle speedometer is more about monitoring speed rather than geographic location, which is not relevant for broadcasting location. A WWV receiver is used for timekeeping and frequency standard transmissions but does not provide locational data. Similarly, a broadcast FM sub-carrier receiver has applications in broadcasting but lacks the capability to indicate a geographical location. Thus, the GPS receiver is uniquely suited for this task, making it the appropriate choice for sending automatic location reports via amateur radio.