In PCM if the transmission path is very long

Options

A. pulse spacing is reduced
B. pulse amplitude is increased
C. pulse width is increased
D. repeater stations are used

Answer

To solve the question regarding the effects of long transmission paths in Pulse Code Modulation (PCM), we will analyze the options provided and determine the correct answer step by step.

### Step-by-Step Solution:

1. **Understanding PCM**:
- PCM stands for Pulse Code Modulation. It is a method used to digitally represent analog signals. In PCM, the amplitude of the analog signal is sampled at regular intervals and then quantized into a series of coded pulses.

2. **Long Transmission Path**:
- When dealing with long transmission paths, the signal can degrade due to various factors such as attenuation, noise, and distortion. This degradation can affect the quality of the transmitted signal.

3. **Options Analysis**:
- **A. Pulse spacing is reduced**: Reducing pulse spacing would mean that the pulses are closer together, which could lead to overlapping and interference, especially over long distances. This is not a typical solution for long-distance transmission.
- **B. Pulse amplitude is increased**: Increasing the pulse amplitude could help in overcoming some attenuation, but it does not address the fundamental issue of long-distance transmission.
- **C. Pulse width is increased**: Increasing pulse width can help in reducing the effects of noise and interference, but it may not be the most effective method for long-distance transmission.
- **D. Repeated stations are used**: This option suggests using repeaters or relay stations to regenerate the signal. This is a common practice in long-distance communication systems to amplify and restore the signal, ensuring it travels the required distance without significant degradation.

4. **Conclusion**:
- The most effective solution for long transmission paths in PCM is to use repeated stations. This method allows the signal to be amplified and retransmitted, maintaining its integrity over long distances.

### Final Answer:
**D. Repeated stations are used**