the lineside railway signal or to the signalling control tower. Euroloop A balise transmits telegrams at a specific site. To allow a continuous transmission the telegrams may be sent along leaky feeder cable being up to 1000 metres long. The Euroloop cable is always connected with a balise at its end which serves as the End of Loop Marker (EOLM). The telegram structure is the same as for the balise it is connected to. Originally the Euroloop used the same frequency as the Eurobalises but that was changed for specification 2.0.1 in September 2004. Euroloops had been used in Switzerland which completed the change in July 2010. Modulation The downlink uses an amplitude modulation on the 27.095 MHz frequency. This frequency is used to power the passive balises (it is the intermediate channel 11A in CB radio). The uplink uses frequency-shift keying with 3.951 MHz for a logical '0' and 4.516 MHz for a logical '1'. The data rate of 564.48 kBit/s is enough to transmit 3 copies of a telegram to a train passing at 500 km/h. The Euroloop frequency was moved to a centre of 13.54750 MHz (exactly half of the Eurobalise power frequency). In a practical setup the BTM requires 65 Watt to power the Eurobalises and to receive the telegrams with the BTM mounted above top of rail on a bogie. Encoding Each pair of balises usually consists of a switchable balise and a fixed balise. A balise transmits a 'telegram' of either 1023 bits (93*11) or 341 bits (31*11) in the channel encoding with 11 bit per symbol. The user data block is cut into 10-bit user symbols before the scrambling and shaping operation - the effective payload of signalling information is 830 bit (83*10) for the long telegram and 210 bit (21*10) for the short telegram. The final telegram consists of shaped data (913 bit or 231 bit) containing the payload (830 or 210 bit) control bits (Cb, 3 bit) scrambling bits (Sb, 12 bit) extra shaping bits (Esb, 10 bit) checksum (CheckBits, 85 bit) The telegram is broadcast in a cyclic manner as the train passes over the balise. To avoid transmission errors the payload is scrambled (avoiding burst errors), substituted with a symbol code of different Hamming distance, and a checksum is added for validity checks. Since the checksum is computed after the symbol substitution the telegram contains extra shaping bits to