Increasing the length of the optical fiber cable _____ the modal bandwidth.

Increasing the length of the optical fiber cable decreases the modal bandwidth. Modal bandwidth is defined as the capacity of a multimode fiber to transmit multiple modes of light simultaneously over a given length.

As the length of the fiber increases, the signal experiences more dispersion, which can lead to a greater overlap of the modes. This overlap causes signals to spread out over time, leading to a degradation in the clarity of the received signal. In simple terms, longer fibers can cause different signals to arrive at different times due to this modal dispersion, which ultimately reduces the fiber's ability to carry data effectively, hence decreasing the modal bandwidth.

While it is clear that modulation schemes, fiber core size, and light source play roles in bandwidth performance, the key relationship established by fiber length is primarily concerned with how increased distance affects signal integrity and the ability to differentiate between modes at the receiving end.