Question E1B01:
[97.3] Which of the following constitutes a spurious emission?  

Choices:  
A: An amateur station transmission made without the proper call sign identification  
B: A signal transmitted to prevent its detection by any station other than the intended recipient  
C: Any transmitted signal that unintentionally interferes with another licensed radio station and whose levels exceed 40 dB below the fundamental power level  
D: An emission outside the signal’s necessary bandwidth that can be reduced or eliminated without affecting the information transmitted    

Correct Answer is  D: An emission outside the signal’s necessary bandwidth that can be reduced or eliminated without affecting the information transmitted  

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Why the correct answer is correct

- Spurious emissions are unwanted emissions outside the necessary bandwidth that can be reduced or eliminated without affecting the information being sent. This includes harmonics, parasitic oscillations, intermodulation, and mixer products.  
- That matches choice D exactly.

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Why the other choices are incorrect

- A: Missing proper call sign ID is a rules violation, not an emission type. It says nothing about the spectral content of the signal.  
- B: A transmission intended to avoid detection (e.g., encryption/obscuration) is about content/intent, not whether the energy is an unwanted byproduct. Not a definition of spurious emission.  
- C: This confuses “interference” with the definition. Interference is not required for an emission to be spurious, and “40 dB below” is not the standard amateur spurious limit. The typical FCC limit is stricter and depends on power.

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Useful formulas and rules of thumb

- Spurious emissions: unwanted emissions unrelated to modulation and reducible without affecting the message; examples include harmonics at $2f_0, 3f_0,\dots$ and mixer products $mf_1 \pm nf_2$.  
- Unwanted emissions = out-of-band emissions + spurious emissions.  
  - Out-of-band emissions arise from the modulation process and are within/near the necessary bandwidth “skirts.”  
  - Spurious emissions are outside the necessary bandwidth and reducible without affecting information.

- Typical amateur spurious emission limit (FCC Part 97.307):  
  $$\text{Spurious level} \le -(43 + 10\log_{10} P)\ \text{dBc}$$  
  where $P$ is transmitter power in watts. Examples:  
  - $P=100\ \text{W}$: $-(43+20) = -63\ \text{dBc}$  
  - $P=10\ \text{W}$: $-(43+10) = -53\ \text{dBc}$  
  - $P=1\ \text{W}$: $-43\ \text{dBc}$

This clarifies that “spurious emission” is about unwanted, reducible spectral components outside necessary bandwidth—not operating practices or the occurrence of interference.