Question E9A11:
Which of the following determines ground losses for a ground-mounted vertical antenna operating on HF?  

Choices:  
A: The standing wave ratio  
B: Distance from the transmitter  
C: Soil conductivity  
D: Take-off angle    

Correct Answer is  C: Soil conductivity  

Correct answer: C — Soil conductivity

Why C is correct:
- A ground-mounted HF vertical uses the earth (and/or a radial system) as its return path. Loss occurs where RF current flows in the soil. The magnitude of that loss is set primarily by the soil’s conductivity, $\sigma$ (S/m). Higher $\sigma$ (e.g., wet, salty soil) means lower loss; lower $\sigma$ (dry, rocky soil) means higher loss.
- Equivalently, soil resistivity $\rho = 1/\sigma$; higher $\rho$ means more loss.

Why the others are incorrect:
- A: Standing Wave Ratio (SWR) only indicates feedline/load mismatch. You can have a perfect SWR while wasting power in ground losses, because matching does not eliminate loss resistance.
- B: Distance from the transmitter is irrelevant. Ground loss is determined in the antenna’s near field at the ground interface, not by how far the rig is from the antenna.
- D: Take-off angle is an outcome influenced by antenna height, pattern, and ground properties, but it does not determine loss. Ground loss is about return-current dissipation in the soil.

Useful formulas and rules of thumb:
- Antenna efficiency:
  $$\eta = \frac{R_r}{R_r + R_g + R_{\text{ohmic}}}$$
  where:
  - $R_r$ = radiation resistance (for a 1/4-wave vertical over a perfect ground, $R_r \approx 36.5\,\Omega$),
  - $R_g$ = ground-loss (return-path) resistance, which increases as soil conductivity decreases,
  - $R_{\text{ohmic}}$ = other losses (e.g., coil/connection resistance).

- Conductivity/resistivity relation:
  $$\rho = \frac{1}{\sigma}$$
  Lower $\rho$ (higher $\sigma$) yields lower $R_g$.

- Skin depth in soil (affects how RF current spreads in the ground):
  $$\delta = \sqrt{\frac{2}{\omega \mu \sigma}}$$
  Larger $\delta$ (from low $\sigma$) implies more lossy volume involved.

- Practical rule of thumb:
  - Better soil (wet/loamy, near salt water) and more/longer radials both reduce $R_g$ and improve efficiency.
  - A dense radial system (e.g., 30–60 radials of roughly $0.2$–$0.25\,\lambda$) can make ground loss only a few ohms; sparse/short radials on poor soil can make $R_g$ tens of ohms.