Question E1B08:
[97.121] What limitations may the FCC place on an amateur station if its signal causes interference to domestic broadcast reception, assuming that the receivers involved are of good engineering design?  

Choices:  
A: The amateur station must cease operation  
B: The amateur station must cease operation on all frequencies below 30 MHz  
C: The amateur station must cease operation on all frequencies above 30 MHz  
D: The amateur station must avoid transmitting during certain hours on frequencies that cause the interference    

Correct Answer is  D: The amateur station must avoid transmitting during certain hours on frequencies that cause the interference  

To calculate what the FCC can require under 47 CFR §97.121 (Restricted operation):

1) Why the correct answer is correct
- The FCC may restrict an amateur station’s operation “as necessary” to eliminate interference to domestic broadcast reception when the affected receivers are of good engineering design.
- Those restrictions can include limiting the station to avoid transmitting during certain hours on the specific frequencies causing the problem. This matches choice D.

2) Why the other choices are incorrect
- A: “The amateur station must cease operation” — Too broad. §97.121 allows the FCC to restrict hours and/or frequencies, not necessarily shut down the station entirely.
- B: “Cease operation on all frequencies below 30 MHz” — The 30 MHz breakpoint is irrelevant. Restrictions target the interfering frequencies, not an entire spectrum range.
- C: “Cease operation on all frequencies above 30 MHz” — Same issue as B; the FCC focuses on the specific frequencies causing interference, not a blanket cutoff.

3) Useful rules of thumb
- If receivers are of good engineering design and there’s interference, the FCC may:
  - Restrict the amateur’s operating hours on the offending frequencies.
  - Require changes to frequency, power, antenna, or other technical parameters.
- If receivers are poorly designed (e.g., lack front-end selectivity), the amateur is generally not required to cease operation; mitigation is still encouraged.
- Definition reminder: “Harmful interference” is that which seriously degrades, obstructs, or repeatedly interrupts a radiocommunication service.