Systems that use licensed, private microwave frequencies for video transmission have been in existence for over 50 years and have supported many live broadcasts. There are three main deployment scenarios in common use for this technology, including fixed links, central antenna systems, and fully portable versions. The equipment and antenna configurations differ among these applications:
Fixed link systems can be used to provide one-way and two-way connections between a pair of fixed locations, such as between a television studio and a transmitter site. Typically, these links use parabolic antennas that are located on towers to permit clear line-of-sight paths.
Central Antenna systems use antenna(s) located at a convenient location for the broadcaster, potentially on top of a tall building in a downtown environment or on the television transmitter tower. These systems can either use multiple fixed antennas pointed in different directions or a movable antenna that can be focused on different locations such as a news helicopter.
Fully Portable systems can be packaged into shipping cases and transported to the location of a shoot. Typically, these systems consist of a combination of camera-back units with omnidirectional antennas and rack-mount electronics packages that are connected to directional antennas that are mounted on portable towers or brackets.
From a technology standpoint, equipment to support these different applications is fairly similar. There are a number of different frequency bands in common usage (2 GHz, 6-7 GHz, 12-13 GHz and some others above 20 GHz). In general, these systems require licensing and frequency coordination, to make sure that each user has a dedicated RF channel to use in a defined area. As a result, the channel bandwidths are limited, forcing the use of video compression and advanced modulation techniques to squeeze as many bits as possible into a narrow frequency band. In addition, there is significant competition for some of these frequencies (particularly those that are desirable for other applications such as mobile telephones and satellite earth stations) which can make obtaining new channel licenses difficult or impossible in some circumstances.