Halesworth. Section entry board and Radio Electronic Token Block RETB radio repeater mast on 10th September 2010. On approaching the board a driver would call up the control centre at Saxmundham by radio and request entry into the advanced section. A token would be delivered by sending data over the analogue radio system, this was displayed in the cab. Once received the driver could proceed. The board was equivalent to a conventional red stop signal. The system was electronically interlocked so that no other train could enter the section at the same time. The RETB control is no longer operational as the system used signals in the 200Mhz band III. The OFCOM operating licence for this frequency band would not have been renewed after the end of 2012 and consequently the RETB system closed on 19th October 2012 and was replaced by conventional signalling, but still locally controlled from Saxmundham. The RETB system was originally introduced on 16th February 1986.