*Question T7A07:
What is the function of a transceiver’s PTT input?*  

*Correct Answer is  B: Switches transceiver from receive to transmit when grounded*  

### AI Response: (may contain errors)  

The correct answer to the question about the function of a transceiver’s PTT (Push-To-Talk) input is:

**B: Switches transceiver from receive to transmit when grounded.**

### Explanation of the Correct Answer:
- The PTT input is designed to control the operation of the transceiver. When the PTT input is grounded (typically by pressing a button), it signals the transceiver to switch from receive mode to transmit mode. This allows the operator to transmit their voice or data over the airwaves.

### Why the Other Choices are Incorrect:
- **A: Input for a key used to send CW**  
  This is incorrect because while a key can be used to send CW (Continuous Wave) signals, the PTT input specifically controls the transition between receive and transmit modes, not just for CW operation.

- **C: Provides a transmit tuning tone when grounded**  
  This is incorrect as the PTT input does not generate a tuning tone. Instead, it simply activates the transmit function of the transceiver. Tuning tones are typically generated by other means, such as a separate tone generator.

- **D: Input for a preamplifier tuning tone**  
  This is also incorrect. The PTT input is not used for tuning tones related to preamplifiers. Preamplifiers may have their own tuning mechanisms, but they do not utilize the PTT input for this purpose.

### Summary:
- The PTT input is essential for controlling the transmit function of a transceiver, allowing operators to switch between receiving and transmitting by grounding the input. Understanding this function is crucial for effective operation in amateur radio.