*Question T4A06:
What signals are used in a computer-radio interface for digital mode operation?*  

*Correct Answer is  C: Receive audio, transmit audio, and transmitter keying*  

### AI Response: (may contain errors)  

The correct answer to the question about signals used in a computer-radio interface for digital mode operation is:

**C: Receive audio, transmit audio, and transmitter keying.**

### Explanation of the Correct Answer:
- **Receive audio**: This is the audio signal received from the radio, which is processed by the computer to decode digital signals.
- **Transmit audio**: This is the audio signal generated by the computer to be sent to the radio for transmission in digital modes.
- **Transmitter keying**: This signal controls the radio's transmitter, turning it on and off as needed for digital communication.

These three components are essential for effective digital mode operation, allowing the computer and radio to communicate properly.

### Why the Other Choices are Incorrect:
- **A: Receive and transmit mode, status, and location**: 
  - This option mentions modes and status, which are not specific signals used in the interface. It lacks the necessary audio signals and keying control.
  
- **B: Antenna and RF power**: 
  - This choice refers to hardware components rather than signals. Antenna and RF power are related to the physical transmission of signals but do not represent the signals exchanged in a computer-radio interface.
  
- **D: NMEA GPS location and DC power**: 
  - NMEA GPS location data is used for navigation and location services, not for digital mode operation. DC power is necessary for operation but is not a signal exchanged in the interface.

### Summary:
In digital mode operation, the key signals exchanged between the computer and the radio are focused on audio input/output and control for transmission. Understanding these components is crucial for effective digital communication in amateur radio.