Editing Communications system (section)

=== Communication channel ===
A communication channel is simply referring to the medium by which a signal travels.  There are two types of media by which electrical signals travel, i.e. '''guided''' and '''unguided'''. Guided media refers to any medium that can be directed from transmitter to receiver by means of connecting cables.  In optical fiber communication, the medium is an optical (glass-like) fiber.  Other guided media might include coaxial cables, telephone wire, twisted-pairs, etc... The other type of media, unguided media, refers to any communication channel that creates space between the transmitter and receiver.  For radio or RF communication, the medium is air.  Air is the only thing between the transmitter and receiver for RF communication while in other cases, like sonar, the medium is usually water because sound waves travel efficiently through certain liquid media. Both types of media are considered unguided because there are no connecting cables between the transmitter and receiver.  Communication channels include almost everything from the vacuum of space to solid pieces of metal; however, some mediums are preferred more than others.  That is because differing sources travel through subjective mediums with fluctuating efficiencies.