*Question E4E06:
What type of electrical interference can be caused by computer network equipment?*  

*Correct Answer is  C: The appearance of unstable modulated or unmodulated signals at specific frequencies*  

### AI Response: (may contain errors)  

Computer network equipment can cause electrical interference that manifests as signals appearing at specific frequencies. This is due to the digital nature of network devices, which can emit radio frequency (RF) noise that affects certain parts of the radio spectrum.

### Explanation:

1. **Correct Answer: C**  
   - **Unstable Modulated or Unmodulated Signals:**  
     Computer network equipment, such as routers and switches, often use digital signals that can inadvertently radiate RF noise. This noise can appear as signals at specific frequencies, which may be modulated (varying in amplitude, frequency, or phase) or unmodulated (constant). These signals can interfere with radio communications by appearing as unwanted signals on certain frequencies.

2. **Why Other Choices Are Incorrect:**
   - **A: A loud AC hum in the audio output of your station’s receiver**  
     - An AC hum is typically caused by power supply issues or ground loops, not by computer network equipment. It is characterized by a steady 60 Hz (or 50 Hz in some regions) hum, which is different from the RF noise emitted by digital devices.
   
   - **B: A clicking noise at intervals of a few seconds**  
     - Clicking noises are often associated with mechanical relays or certain types of digital circuits, but they are not a typical symptom of interference from computer network equipment.
   
   - **D: A whining-type noise that continually pulses off and on**  
     - A whining noise is more characteristic of switching power supplies or other electronic devices with oscillating circuits, rather than computer network equipment.

### Useful Tips:
- **Digital Devices and RF Noise:**  
  Digital devices can emit RF noise due to their high-speed switching operations. This noise can couple into radio equipment, especially if the equipment is not well-shielded or if the antenna is in close proximity to the noise source.
  
- **Mitigation:**  
  To reduce interference from computer network equipment, consider using ferrite beads on cables, improving equipment shielding, and maintaining physical separation between network devices and radio equipment.