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Part 1 of this story discussed the mechanical and phased-array features of the TracVision hybrid antenna.
Another major hurdle in designing the KVH Industries TracVision A7 was in acquiring and staying locked onto satellite signals while mounted on a moving vehicle that can rapidly change direction and speed. The solution to getting the optimum signal as the vehicle maneuvers involves nimble drive motors and smart software. The horizontal drive motor, for example, can spin the antenna up to 70°/second, allowing the unit to stay locked onto a satellite even when the vehicle is turning rapidly. A second motor precisely tilts the antenna via a two-piece, elevation drive link.
The TracVision A7 antenna remains pointed at the DIRECTV satellite regardless of what direction the vehicle turns.
Once the motors and the tracking software have acquired and locked on to the signals from a satellite, the question becomes what happens should the vehicle pass behind a large building or though an underpass? The loss of signal doesn't mean the A7 has to initiate a new search for the satellite; KVH engineers equipped the antenna with two rate gyros. These units provide directional stability and allow the antenna to maintain its aim on that point from which the signals were last received.
When the vehicle moves from behind the building or emerges from the underpass, the A7 antenna is still pointing at the satellite and quickly reacquires the signal.
The TracVision A7 measures vehicle motion so that when temporarily blocked, the antenna remains pointed at the satellite for resumption of reception once the blockage is cleared.
Multi-satellite capability
Another advantage of the A7 design is its multi-satellite capability. Unlike the earlier TracVision A5, which could only tune to the signals from the DIRECTV satellite positioned at 101° west longitude, the A7 can tune in to the signals from any of four DIRECTV satellites orbiting above the Equator at 72° west, 101° west, 110° west, and 119° west. Thanks to direct, digital communication between the antenna and the receiver, the A7 can smoothly transition from one satellite to either of the other three satellites should the user wish to access programming on a different DIRECTV satellite.
Integrated GPS receiver
A second major improvement in the TracVision A7 is the incorporation of a dedicated GPS receiver inside the antenna enclosure. The ready access to GPS-derived position, heading, and course-over-the-ground data boosts the effectiveness of the A7 and opens possibilities for new services from KVH and DIRECTV in the future.
A GPS receiver (center) is built into the TracVision A7 system next to the hybrid antenna array.
Local channels in designated market areas
DIRECTV broadcasts the majority of its national channels (e.g., CNN, ESPN, The Weather Channel, A&E, etc.) via a single satellite at 101° west. However, to support the growing number of local markets that receive local service and network TV (ABC, CBS, FOX, NBC, and PBS) via DIRECTV, the service provider uses the satellites at 72° west and 119° west to carry that specific, regional programming.
Local network programming in the DIRECTV system is broken down by individual cities and their corresponding geographic areas. These zones are known as designated market areas (DMAs). Local programming is tied to a DMA and is not available outside that DMA. Thus, Atlanta local programs are not available in Charleston and vice versa.
For home-based users of DIRECTV, this arrangement is not an issue, since their satellite receivers are set to receive the programs in their DMA only. Mobile users, however, present a problem as they can pass between DMAs. Local broadcasters within each DMA require that their programming only be available to mobile users with residences in that DMA. Once a DIRECTV user crosses the border of his or her DMA, the local programming is no longer available. Implementing this plan, however, requires that the satellite receiver in the vehicle "know" it has crossed the DMA boundary.
The ability to sense whether a mobile receiver is inside or outside a particular DMA is provided by the GPS unit in the A7. The A7 receiver has a detailed database of DMA boundaries. During initial setup, the user inputs his or her home address, which is correlated with the DMA database. The receiver knows the user's home DMA and it knows the latitude and longitude boundaries of that DMA. As long as the vehicle remains within the DMA, local programming remains available. Should the vehicle leave the DMA, local programming is automatically blocked by the A7 receiver. Full national programming always remains available to the mobile user.
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