*Question G4B04:
What signal source is connected to the vertical input of an oscilloscope when checking the RF envelope pattern of a transmitted signal?*  

*Correct Answer is  D: The attenuated RF output of the transmitter*  

### AI Response: (may contain errors)  

To check the RF envelope pattern of a transmitted signal using an oscilloscope, you connect the vertical input to the attenuated RF output of the transmitter. Here's why this is the correct choice and why the others are not:

### Correct Answer: D - The attenuated RF output of the transmitter
- **Explanation**: The RF envelope pattern represents the modulation of the transmitted signal over time. By connecting to the attenuated RF output, you can observe the actual signal being transmitted, including its amplitude variations that correspond to the modulation. Attenuation is necessary to prevent damage to the oscilloscope and to ensure accurate readings.

### Why the Other Choices are Incorrect:
- **A: The local oscillator of the transmitter**
  - **Explanation**: The local oscillator generates a stable frequency used for mixing but does not represent the transmitted signal's envelope. It is not modulated and therefore does not provide the information needed to analyze the RF envelope pattern.

- **B: An external RF oscillator**
  - **Explanation**: An external RF oscillator produces a continuous wave (CW) signal that is not modulated in the same way as the transmitted signal. It cannot provide the envelope pattern of the actual transmission, which is what you need to analyze.

- **C: The transmitter balanced mixer output**
  - **Explanation**: The balanced mixer output is used to combine signals and create the desired frequency for transmission. However, it does not directly represent the RF envelope of the transmitted signal, as it may contain unwanted frequencies and does not reflect the modulation characteristics.

### Summary
To analyze the RF envelope pattern, always connect to the attenuated RF output of the transmitter. This allows you to see the modulation and amplitude variations that are critical for understanding the transmitted signal's characteristics.