What is a primary cause of bit errors in digital modulation channels?

The primary cause of bit errors in digital modulation channels is often attributed to hum and impulse noise. This type of noise can disrupt the integrity of the signal being transmitted. Hum typically arises from electromagnetic interference from power lines or other electronic equipment, while impulse noise can be caused by sudden disturbances, such as electrical surges or lightning strikes.

When these forms of noise are present in a digital communication channel, they can distort the signals and lead to incorrect interpretation of the data at the receiver, resulting in bit errors. These errors can compromise the reliability of communication systems and degrade overall performance.

On the other hand, overwhelming signal strength, poor quality cables, and improperly calibrated modems can contribute to issues in transmission but are not as direct a cause of bit errors as noise is. For instance, overwhelming signal strength can lead to signal distortion or clipping, which may introduce errors, but it is not as universally impactful as the presence of hum and impulse noise. Similarly, poor quality cables can affect signal quality but typically do not directly create bit errors independent of other factors such as noise. Lastly, improperly calibrated modems may result in poor modulation or demodulation performance, but these issues often stem from noise interference as well.