Question E9H06:
What indicates the correct value of terminating resistance for a Beverage antenna?  

Choices:  
A: Maximum feed point DC resistance at the center of the desired frequency range  
B: Minimum low-angle front-to-back ratio at the design frequency  
C: Maximum DC current in the terminating resistor  
D: Minimum variation in SWR over the desired frequency range    

Correct Answer is  D: Minimum variation in SWR over the desired frequency range  

Correct answer: D — Minimum variation in SWR over the desired frequency range

1) Why D is correct
- A Beverage is a terminated traveling-wave antenna. The far-end terminating resistor should equal the antenna’s characteristic impedance, $Z_0$, so the wave is absorbed with minimal reflection.
- When $R_T \approx Z_0$, the reflection coefficient is near zero and the feed system looks broadband and “flat,” so the SWR changes very little with frequency (even if it isn’t exactly 1:1).
- In terms of transmission-line behavior:
  $$\Gamma = \frac{Z_L - Z_0}{Z_L + Z_0}, \quad SWR = \frac{1 + |\Gamma|}{1 - |\Gamma|}$$
  Setting $Z_L = R_T = Z_0$ gives $\Gamma \approx 0$, minimizing standing waves and making SWR vs. frequency as flat as possible.

2) Why the other choices are incorrect
- A: “Maximum feed point DC resistance...”  
  DC measurements don’t indicate the correct RF terminating value. The Beverage’s performance depends on RF impedance and reflections, not DC resistance.
- B: “Minimum low-angle front-to-back ratio...”  
  You want maximum front-to-back (good directivity), not minimum. A wrong termination increases reflections and degrades F/B.
- C: “Maximum DC current in the terminating resistor”  
  The termination dissipates RF, not DC. There’s no meaningful DC current in the resistor during normal receive operation.

3) Useful formulas and rules of thumb
- Use the reflection/SWR relations:
  $$\Gamma = \frac{Z_L - Z_0}{Z_L + Z_0}, \quad SWR = \frac{1 + |\Gamma|}{1 - |\Gamma|}$$
- For best performance, choose $R_T \approx Z_0$ of the Beverage. Typical $Z_0$ values are a few hundred ohms (often 400–800 Ω depending on height and ground). A common starting point is 470–560 Ω, then tweak for the flattest SWR across the band.
- Proper termination yields:
  - Broad bandwidth and stable SWR vs. frequency
  - Best unidirectional pattern (highest front-to-back)
  - Minimal reflections and ripple in response across the band