I take the point on abbreviations;
ES = extended squitter
ADS-B = Automatic Dependent Surveillance Broadcast
When the CAA decided not to implement the original idea that everything that flew had to have mode s, it embarked on a three-point plan. Phase 2 will complete in March 2012. Phase three, which did not have a fixed timeframe, was the addition of ADS-B (Automatic Dependent Surveillance Broadcast ) using the ES (extended squitter) feature of mode s transponders. This allows for the transmission of additional data, including position, heading and speed.
In order for the Mode s transponder to transmit this data it needs to get it. The source is a GPS. Just about any aviation GPS can do this, but I imagine it will not be as simple as that in Europe.
When the avionic shops were advertising the Mode S was coming fit it quick, Garmin were rubbing their hands together with glee. Unfortunately a number of companies launched fully approved units at significantly lower cost. In response Garmin launched a low cost unit called the 328. This unit is the only mode S unit I know of which does not support ES so cannot be used for ADS-B. The avionic shops pushed this unit for all they were worth. The CAA warned against fitting it at various consultation meetings. The unit is the most popular Mode S unit in the UK by some way. When ADS-B comes in there are going to be some very unhappy pilots, and some very happy avionic shops.
In a sensible world the CAA would have encouraged people to enable ADS-B on installation of an appropriate transponder (assuming a suitable GPS was available). Far from it! To enable it they decide it was a major mod costing £1000’s.
Hope that helps!
Rod1