*Question E9F11:
What impedance does a 1/8-wavelength transmission line present to an RF generator when the line is open at the far end?*  

*Correct Answer is  C: A capacitive reactance*  

### AI Response: (may contain errors)  

When dealing with transmission lines, the impedance presented to an RF generator depends on the length of the line and the termination at the far end. For a 1/8-wavelength transmission line that is open at the far end, the impedance transformation can be understood as follows:

1. **Correct Answer: A capacitive reactance (C)**

   - A 1/8-wavelength transmission line transforms the open circuit at the far end into a capacitive reactance at the input. This is because the line is less than a quarter wavelength, and the open end causes the line to behave like a capacitor.
   - The impedance transformation for a line that is less than a quarter wavelength and open at the end results in a capacitive reactance. This is due to the phase shift introduced by the line length, which is less than 90 degrees (a quarter wavelength).

2. **Why the other choices are incorrect:**

   - **A: The same as the characteristic impedance of the line**  
     This would be true if the line were terminated in its characteristic impedance, but an open circuit does not match the characteristic impedance.

   - **B: An inductive reactance**  
     An inductive reactance would occur if the line were shorted at the far end and less than a quarter wavelength. Since the line is open, it presents a capacitive reactance instead.

   - **D: Infinite**  
     An infinite impedance would be seen if the line were exactly a half-wavelength long and open at the end. At 1/8-wavelength, the impedance is not infinite.

3. **Useful Rule of Thumb:**

   - For a transmission line that is open at the far end:
     - If the line is less than a quarter wavelength, it presents a capacitive reactance.
     - If the line is more than a quarter wavelength but less than a half wavelength, it presents an inductive reactance.

Understanding these transformations helps in predicting how transmission lines will behave in different configurations, which is crucial for designing and troubleshooting RF systems.