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

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

### AI Response: (may contain errors)  

The terms "L band" and "S band" refer to specific frequency ranges used in radio communications, particularly in satellite and radar systems.

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

1. **Why the correct answer is correct:**
   - The "L band" typically refers to frequencies in the range of 1 to 2 GHz, which corresponds to the 23-centimeter band in amateur radio.
   - The "S band" refers to frequencies in the range of 2 to 4 GHz, which corresponds to the 13-centimeter band in amateur radio.
   - These designations are part of the IEEE frequency band nomenclature, which is widely used in various communication fields.

### Why the other choices are incorrect:

- **B: The 2-meter and 70-centimeter bands**
  - The 2-meter band is in the VHF range (144-148 MHz), and the 70-centimeter band is in the UHF range (420-450 MHz). These do not correspond to the L and S bands.

- **C: FM and digital store-and-forward systems**
  - These terms refer to types of communication systems and methods, not specific frequency bands.

- **D: Which sideband to use**
  - Sidebands (upper or lower) are related to amplitude modulation techniques and do not specify frequency bands like L and S bands do.

### Useful Information:

- **Frequency to Wavelength Conversion:**
  - Wavelength ($\lambda$) in meters can be calculated from frequency ($f$) in GHz using the formula:
    $$ \lambda = \frac{300}{f} $$
  - For example, a frequency of 1.3 GHz (L band) corresponds to approximately 23 centimeters, and 2.4 GHz (S band) corresponds to approximately 13 centimeters.

Understanding these frequency designations helps in identifying the appropriate bands for specific applications, especially in satellite communications.