Eurobalise
In response to "telepowering" by means of a 27 MHz, CW-modulated magnetic field transmitted by a Balise Transmission Module [de] (BTM and its associated antenna) mounted under a passing train, the balise transmits information to the train (uplink) by means of a 4.234 MHz FSK-modulated magnetic field.
The BTM may be integrated into the on-board antenna or a separate electronic module, according to the preference of the system vendor.
Thus a fixed balise can notify a train of its exact location, and the distance to the next signal, and can warn of any permanent speed restrictions.
ETCS and other applications using Eurobalise technology typically include protection against failure and theft of balises.
Alternatively, in ETCS application levels 2 and 3, the "link list" may be transmitted to the trainborne equipment from the Radio Block Centre (RBC).
The reaction that the trainborne equipment shall apply in case of a missing or failed balise is itself defined by data transmitted with the link list and could typically be to make an enforced brake application or to display a message to the train driver.
Balises also provide a set of fixed position references to the ETCS onboard equipment, allowing the latter to correct its odometry system for cumulative errors accrued during travel from one balise group to the next and maintain accurate tracking of its position relative to the end point of the current movement authority.
These errors typically result from slippage and sliding of the train wheels on damp rails, or from controlled-creep traction.
Balise designs usually include multiple redundant electronic circuitry, allowing them to continue providing normal service for many years despite partial failure.
It may also contain track information such as route suitability data for different train types and axle load restrictions.
Almost all packet types contain a parameter flagging whether its information is relevant for the "nominal" or "reverse" direction (or both).
Similarly the international static speed profile is given in a variable count of section parts with each part denoting the section length (number in meters - the scale is only given once at the start of the packet for all sections), the maximum speed (number * 5 km/h - allowed numbers are 0-120 i.e. some spare values are left over) and a flag if the speed restriction applies to the front or rear end of the train (possibly allowing for a delay).
[5] The history of ETCS has seen the formation of UNISIG (Union of Signalling Industry) in 1998 to promote the development of the system.
The group has ensured that Eurobalises may be made by several different companies; while the balises may vary in the details, they are manufactured to meet the same standards.
The principal manufacturers of Eurobalises belong to a group[6] of seven firms (Alstom, Ansaldo STS, Bombardier, Invensys, Siemens, Sigma-Digitek, Thales) within the UNIFE federation of railway suppliers.
There are alternative implementations that pick up on the telegram structure to encode only some packet types and adding additional specific information.
The additional telegram packet types for tilting trains have been added to the Baseline 3 series of ETCS.
This allowed for the first drafts of the new technology and since 1996 the elements were tested by six railway operators which had joined the ERTMS user group.
[2] Another source for the technology comes from the Siemens ZUB 100 family where they used coupling coils at the side of the tracks to augment the existing train protection system with additional signalling.
So 1998 saw the formation of UNISIG (Union of Signalling Industry), including Alstom, Ansaldo, Siemens, Bombardier,[a] Invensys and Thales which were to take over the finalisation of the standard.
[13] The first baseline specification has been tested by six railways since 1999 as part of the European Rail Traffic Management System[14] The railway companies defined some extended requirements that were added to ETCS including telegram packet types for RBC-Handover and track profile information - the resulting Class 1 Version 2.0.0 specification of ETCS was then published in April 2000.
