## Gain distortion – the channel

#### The channel itself can introduce gain distortion via a variety of mechanisms. Wired channels exhibit a general roll-off of amplitude with frequency due to the capacitive nature of long lengths of cable causing a low pass filtering effect. Also, poor termination of cables at the end-user equipment can itself introduce distortion. Some telephone lines in particular exhibit a very poor amplitude response. Wireless links do not suffer the capacitance problems of cables, but instead suffer from variable path loss due to the unpredictable nature of the communications path. This path loss can be either flat with frequency, or frequency dependent, depending on the bandwidth of the modulation signal, the operating frequency and the path distance. These issues are dealt with more fully in Section 4.5. |