*Question E1C10:
[97.307] What is the maximum mean power level for a spurious emission below 30 MHz with respect to the fundamental emission?*  

*Correct Answer is  A: - 43 dB*  

### AI Response: (may contain errors)  

In the context of amateur radio, spurious emissions are unwanted signals emitted by a transmitter outside of its intended frequency band. The Federal Communications Commission (FCC) sets limits on these emissions to minimize interference with other communications.

### Explanation:

1. **Correct Answer: -43 dB**

   - The FCC regulation [97.307] specifies that for frequencies below 30 MHz, the maximum mean power level of a spurious emission must be at least 43 dB below the power level of the fundamental emission. This means that the spurious emissions should be significantly weaker than the main signal to prevent interference.

2. **Why Other Choices Are Incorrect:**

   - **Choice B: -53 dB**
     - While a reduction of 53 dB would be even more stringent, the regulation specifically requires a minimum of 43 dB below the fundamental. Therefore, -53 dB is not the correct answer for the minimum requirement.

   - **Choice C: -63 dB**
     - Similar to choice B, -63 dB is more stringent than necessary. The regulation does not require spurious emissions to be this low relative to the fundamental emission.

   - **Choice D: -73 dB**
     - This is an even more stringent requirement than -63 dB. While lower spurious emissions are generally better, the regulation only mandates a minimum of 43 dB below the fundamental.

### Useful Rule of Thumb:

- **Spurious Emission Limit Below 30 MHz:**
  - The spurious emission must be at least 43 dB below the fundamental emission. This is a key point to remember for the exam.

By understanding these limits, amateur radio operators can ensure their equipment complies with FCC regulations, reducing the risk of interference with other communications.