Here's why:

* Baud Rate: Baud rate represents the number of symbol changes per second in a digital communication system. A symbol can be a bit (0 or 1), or a more complex combination of bits.

* Square Wave Frequency: The frequency of a square wave represents the number of cycles per second. A cycle is one complete transition from high to low and back to high.

Relationship:

* Simple Case: In some simple systems where each bit is represented by one square wave cycle (high for a bit 1, low for a bit 0), then the baud rate and frequency are equal.

* Complex Cases: However, many communication systems use more complex encoding schemes:

* Multi-level Encoding: A single symbol can represent multiple bits, requiring more than one square wave cycle. In this case, baud rate is lower than the frequency.

* Line Coding: The square wave shape might be modified to represent data. For example, Manchester encoding uses a transition at the middle of each bit period. The baud rate remains the same, but the frequency might be higher due to the additional transitions.

Example:

* A system transmits data at 100 baud. If each bit is represented by one square wave cycle, the frequency of the square wave is also 100 Hz.

* However, if the system uses a 4-level encoding (each symbol represents 2 bits), the frequency of the square wave could be 200 Hz (twice the baud rate) to accommodate the additional transitions.

Conclusion:

The frequency of the square wave used in digital communication is not always directly equal to the baud rate. It depends on the encoding scheme used to represent data.