Proceedings 2002/2003 - IRSE

EUROBALISE TRANSMISSION SYSTEM, A TECHNICAL OVERVIEW 27
In general, the detailed specification of the balise
is very rigid leaving a minimum of flexibility, whilst
the specification of the on-board transmission
equipment is fairly flexible in order to allow various
alternatives for on-board optimisation.
4.2 EUROBALISE
A Eurobalise is interrogated and tele-powered by
an inductively coupled tele-powering signal. The
response of the Eurobalise is also an inductively
coupled up-link signal. Source and sink of the
tele-powering signal and the up-link signal respectively
is the vehicle mounted antenna unit.
Figure 3 – Eurobalise and its Main Interfaces
The origin of the data carried by the up-link signal
is a non-volatile memory in a fixed Eurobalise, or a
serial data-link (the balise control interface) in a
controlled Eurobalise. The data in the non-volatile
memory is programmed on installation of the
Eurobalise. If the Balise Controlling Interface is
disturbed or interrupted, a controlled Eurobalise
automatically switches over to transmitting the
telegram in its internal non-volatile memory (which is
also fitted in controlled Eurobalises).
The Lineside Electronic Unit (LEU) receives
messages from the wayside signalling or the interlocking.
They are converted into Eurobalise
telegrams (fulfilling the requirements of the telegram
format), and are passed through the balise control
interface to the Eurobalise, which transmits them to
the on-board transmission equipment on passing
trains.
The Eurobalise generates a field that is picked up
by the on-board antenna unit. Current flowing in the
transmitting loop in the Eurobalise induces a voltage
in the reception loop in the antenna unit.
Two frequencies are used for frequency shift
keying (FSK) of the up-link data, approximately 3.9
MHz for a logical 0 and 4.5 MHz for a logical 1. In a
shift between the two frequencies the carrier has a
continuous phase (ie the modulation is continuousphase
FSK). The centre frequency is approximately
4.2 MHz and the frequency deviation is approximately
282 kHz. The mean data rate is approximately
565 kbit/s. Figure 4 below shows an
example.
Two sizes of Eurobalise are defined, Standard size
and Reduced size. The Reduced size Eurobalise can
be installed transversely (ie with its longer side at
right angles to the track) or longitudinally as
required.
Standard and Reduced size Eurobalises have the
following reference areas for defining the field
strength from an antenna unit as well as their own
output field strength:
• Standard size Eurobalise – active reference area
358mm by 488mm;
• Reduced size Eurobalise – active reference area
200mm by 390mm.
The physical size of the actual Eurobalise is
somewhat larger in each case because of the need
for encapsulation, and the thickness is a few
centimetres.
Obviously, Eurobalises will be used in a large
variety of environmental conditions. In particular
they will be subjected to various kinds of débris (eg
water, salt water, snow, ice, iron ore, etc). In order to
provide some flexibility in this specific respect
Eurobalises are subdivided into two classes, Class A
and Class B. Class A Eurobalises are intended to be
used in a more demanding environment than Class
B Eurobalises.
Eurobalises can be mounted within an overall
range from 93mm to 210mm below the top of the
rail. This applies to the entire family of Eurobalises.
Each separate type (Standard size, Reduced size,
Class A, Class B, etc) has limitations and does
not necessarily cover the full range. In some cases
the range is also limited if the balise is installed
where certain defined types of metallic structures
exist.
Eurobalises are mounted in the middle of the track
Figure 4 – FSK Up-link Signal from Eurobalise