*Question E9F07:
How does parallel conductor transmission line compare to coaxial cable with a plastic dielectric?*  

*Correct Answer is  A: Lower loss*  

### AI Response: (may contain errors)  

To understand the comparison between parallel conductor transmission lines and coaxial cables with a plastic dielectric, let's break down the correct answer and the other choices.

### Correct Answer: Lower loss

- **Explanation**: Parallel conductor transmission lines, such as open wire lines, typically have lower loss compared to coaxial cables. This is because:
  - They have less dielectric material, which can introduce losses.
  - The air gap between the conductors reduces dielectric losses, making them more efficient for RF transmission, especially at higher frequencies.

### Why the Other Choices are Incorrect:

- **B: Higher SWR**  
  - **Explanation**: Standing Wave Ratio (SWR) is a measure of impedance matching. A parallel conductor line can have a lower SWR if properly matched to the load. Coaxial cables can also have high SWR if not matched, but this is not a characteristic of the transmission line type itself.

- **C: Smaller reflection coefficient**  
  - **Explanation**: The reflection coefficient is related to how well the transmission line is matched to the load. Both parallel lines and coaxial cables can have similar reflection coefficients depending on their design and matching. Thus, this statement does not hold true universally.

- **D: Lower velocity factor**  
  - **Explanation**: The velocity factor is determined by the dielectric material and the geometry of the transmission line. Coaxial cables typically have a velocity factor around 0.66 to 0.95, depending on the dielectric. Parallel lines can have a similar or even higher velocity factor due to the air dielectric, making this statement incorrect.

### Summary

- **Key Takeaway**: Parallel conductor lines generally exhibit lower losses than coaxial cables due to reduced dielectric effects and better efficiency at RF frequencies.
- **Useful Rule of Thumb**: For RF applications, open wire lines are often preferred for long-distance transmission due to their lower loss characteristics compared to coaxial cables.