Automation

Automation has entered the broadcast process in all areas to varying degrees, and SNG is no exception. This may sound a little odd, considering the unpredictable way in which SNG systems are set up and used – after all, it is not like automating a process in a broadcast centre. But in these days of constant downward pressure of costs, combined with the element of multi-skilling that has increased in many areas, there is a natural attraction towards the use of automated processes if it saves money.

So some automation is possible, and there are two principal types of process which can be automated – acquisition of the satellite and remote operation of the system.

Automated acquisition of the satellite

The most difficult task in the operation of any SNG system, which by its very nature is never in one place for very long, is acquiring the bird. The satellite can be an elusive object to identify at times for even the most experienced operators, but the process can, surprisingly, be relatively easily automated for most operations which are based on a vehicle.

A satellite occupies a position in space that is defined by two parameters in relation to a particular location – its azimuth and elevation. By the co-ordinated usage of two devices, an automated system can be devised to find a satellite. It has to be said that this type of automated system is only suited for a vehicle-mounted rather than a flyaway system.

The two devices are a GPS unit, and a flux-gate compass. They are used in conjunction with a microprocessor control system that has satellite orbital positions programmed. This control system can then drive the antenna to the correct azimuth and elevation for the required satellite.

GPS

The Global Positioning System (GPS) was developed in the 1970s by the US Department of Defense to provide highly accurate location data, and using a constant stream of timing information generated from a highly accurate atomic clock on each satellite, GPS receivers fitted with clocks read this information. By comparing the signal from each satellite with the time in its own clock, the GPS receiver calculates the distance to each satellite and adjusts its own clock, then uses triangulation techniques to calculate its location, providing positional information accurate to less than one metre for military use. It is the technology behind the ability to provide the military with the exact positional information required for modern warfare, including the precise information required by ‘smart’ bombs and missiles.

The service is available to be used by commercial manufacturers of GPS equipment, albeit at a ‘degraded’ quality that still allows positioning to be accurate to less than 10 m. The satellites send out signals which a GPS receiver can lock onto and determine its position. The GPS unit needs to receive signals from at least three different satellites in the system to be able to accurately determine its position, and a signal from a fourth to determine its altitude. These receivers are available in many countries at very economical prices (under 200 US dollars).

GPS technology is widely used for all forms of navigation. It is also used in automated satellite acquisition systems to provide the longitude and latitude information to determine the look angle of the required satellite for antenna positioning.

The flux-gate compass is a very accurate electromagnetic compass which provides an accurate bearing (heading), and this is referenced to a nominal reference direction – usually the direction the vehicle is pointing or the antenna is normally sitting at after deployment.