*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 need to visualize the actual RF signal being transmitted. Here's why the correct answer is D: The attenuated RF output of the transmitter.

1. **Correct Answer: D - The attenuated RF output of the transmitter**
   - The RF envelope pattern represents the modulation characteristics of the transmitted signal. By connecting the attenuated RF output to the vertical input of the oscilloscope, you can directly observe the amplitude variations over time, which is the envelope of the RF signal.
   - Attenuation is necessary to ensure the signal level is within the safe input range of the oscilloscope, preventing damage to the equipment.

2. **Why the other choices are incorrect:**
   - **A: The local oscillator of the transmitter**
     - The local oscillator signal is not modulated with the information being transmitted. It is used for frequency conversion and does not represent the RF envelope.
   - **B: An external RF oscillator**
     - An external RF oscillator would provide a continuous wave (CW) signal, which does not contain the modulation information needed to observe the RF envelope pattern.
   - **C: The transmitter balanced mixer output**
     - The balanced mixer output is typically an intermediate frequency (IF) signal, not the final RF output. It does not represent the final modulated RF envelope.

In summary, to observe the RF envelope pattern, you need the actual modulated RF signal, which is available at the attenuated RF output of the transmitter. This allows you to see how the signal's amplitude changes over time, reflecting the modulation applied to the carrier.