*Question G9C11:
What is a beta or hairpin match?*  

*Correct Answer is  A: A shorted transmission line stub placed at the feed point of a Yagi antenna to provide impedance matching*  

### AI Response: (may contain errors)  

A beta or hairpin match is a method used to match the impedance of a Yagi antenna to the transmission line, ensuring maximum power transfer. Here's why the correct answer is A:

1. **Correct Answer (A):**  
   - A beta or hairpin match involves using a shorted transmission line stub at the feed point of a Yagi antenna. This stub is typically a short piece of wire or rod that is parallel to the driven element and is shorted at one end. It acts as an inductive reactance that cancels out the capacitive reactance of the antenna, thus providing impedance matching.

2. **Why Other Choices Are Incorrect:**
   - **Choice B:** A 1/4 wavelength section of 75-ohm coax is a different type of matching technique known as a quarter-wave transformer. It is not a beta or hairpin match.
   - **Choice C:** A series capacitor is used to cancel inductive reactance, not capacitive reactance, and is not part of a beta or hairpin match.
   - **Choice D:** A section of 300-ohm twin-lead is used for matching folded dipole antennas, but it is not related to the beta or hairpin match used in Yagi antennas.

3. **Useful Concepts:**
   - The beta or hairpin match is effective because it transforms the impedance at the feed point to match the transmission line, typically 50 ohms.
   - The length and position of the hairpin stub are critical for achieving the desired impedance transformation.

Understanding these concepts will help you recognize the correct matching techniques for different antenna setups on the exam.