*Question E4E09:
What undesirable effect can occur when using a noise blanker?*  

*Correct Answer is  C: Strong signals may be distorted and appear to cause spurious emissions*  

### AI Response: (may contain errors)  

When using a noise blanker, the correct answer is:

**C: Strong signals may be distorted and appear to cause spurious emissions**

### Explanation:

1. **Why the correct answer is correct:**
   - A noise blanker is designed to reduce impulsive noise, such as ignition noise from engines. It works by momentarily muting the receiver during noise pulses. However, when a strong signal is present, the noise blanker can mistakenly interpret parts of the strong signal as noise. This can lead to distortion of the strong signal, causing it to appear as if it is generating spurious emissions.

2. **Why the other choices are incorrect:**
   - **A: Received audio in the speech range might have an echo effect**
     - Noise blankers do not introduce echo effects. Echoes are typically related to multipath propagation or digital signal processing issues, not noise blanking.
   
   - **B: The audio frequency bandwidth of the received signal might be compressed**
     - Noise blankers do not compress the audio frequency bandwidth. They are designed to eliminate noise pulses, not alter the bandwidth of the received signal.
   
   - **D: FM signals can no longer be demodulated**
     - Noise blankers are generally used in AM and SSB modes, where impulsive noise is more problematic. FM signals are less affected by impulsive noise due to their constant amplitude nature, and noise blankers do not typically affect FM demodulation.

### Useful Rule of Thumb:

- **Noise Blanker Effect:** While effective at reducing impulsive noise, noise blankers can cause distortion in the presence of strong signals, leading to apparent spurious emissions. This is a trade-off to be aware of when using this feature.