Question E2A09:
What do the terms “L band” and “S band” specify?  

Choices:  
A: The 23- and 13-centimeter bands  
B: The 2-meter and 70-centimeter bands  
C: FM and digital store-and-forward systems  
D: Which sideband to use    

Correct Answer is  A: The 23- and 13-centimeter bands  

L band and S band are letter designations for microwave frequency ranges. In amateur radio use:
- L band ≈ 1–2 GHz, which includes the 23 cm band (around 1.24–1.30 GHz).
- S band ≈ 2–4 GHz, which includes the 13 cm band (around 2.30–2.45 GHz).

Why A is correct:
- The 23 cm band (~1.3 GHz) lies in L band.
- The 13 cm band (~2.3–2.45 GHz) lies in S band.

Why the others are incorrect:
- B: 2 meters (144–148 MHz) and 70 cm (420–450 MHz) are VHF/UHF, below L/S microwave ranges.
- C: FM and digital store-and-forward are modes/systems, not frequency bands.
- D: Sideband choice (USB/LSB) is unrelated to L/S band designations.

Useful formulas and rules of thumb:
- Wavelength–frequency relation: $$\lambda(\text{m}) = \frac{300}{f(\text{MHz})}$$
- In cm/GHz: $$f(\text{GHz}) \approx \frac{30}{\lambda(\text{cm})}$$
  - 23 cm: $f \approx 30/23 \approx 1.30$ GHz → L band.
  - 13 cm: $f \approx 30/13 \approx 2.31$ GHz → S band.