<Li> The radio channel between an amateur radio repeater and a ham uses two frequencies often 600 kHz (0.6 MHz) apart . For example, a repeater that transmits on 146.94 MHz typically listens for a ham transmitting on 146.34 MHz . </Li> <P> All of these communications channels share the property that they transfer information . The information is carried through the channel by a signal . </P> <P> A channel can be modelled physically by trying to calculate the physical processes which modify the transmitted signal . For example, in wireless communications the channel can be modelled by calculating the reflection off every object in the environment . A sequence of random numbers might also be added in to simulate external interference and / or electronic noise in the receiver . </P> <P> Statistically a communication channel is usually modelled as a triple consisting of an input alphabet, an output alphabet, and for each pair (i, o) of input and output elements a transition probability p (i, o). Semantically, the transition probability is the probability that the symbol o is received given that i was transmitted over the channel . </P>

Which of the following is an example of a communication channel