Home Page > Section 19; pages: 1, 2

Section 19: Signs associated with Radio Systems

(Page 1 of 2)


Radio communication became an established feature on Britain's railways from the 1980s and spread rapidly until the whole network came to be covered by at least one variety of radio system. The original analogue systems are gradually being supplanted by newer digital systems.


Radio systems were installed on some lines in the north of Scotland in the early 1980s in preparation for the eventual introduction of Radio Electronic Token Block (RETB) signalling. Some rather basic signs were installed at the places where the channel had to be changed [19.1 & 19.2]. When the Regional Operations Manager travelled over the Inverness - Aberdeen line in 1985, he saw what he referred to as "painted bits of wood with radio channel change information on them". He demanded that they be changed to circular or octagonal boards with yellow letters on a blue background, but they never were.

[19.1] Channel Change Board (Dingwall - Kyle of Lochalsh line). Status: Obsolete [19.2] Channel Change Board (Inverness - Aberdeen line). Status: Obsolete Click Here for Photo

An in-cab radio system was a safety requirement for the introduction of "Driver Only Operation" (DOO), meaning the working of trains without a guard. The radio allows the driver to remain in the cab and communicate with the signalman when stopped at a signal, rather than using the signal post telephone. The system is secure, in that the driver and signalman can communicate on a one to one basis and not be heard by anyone else. The signalman has the facility to transmit a general message to all drivers in a particular area. The system was first applied in the Glasgow area in 1986, being referred to originally as the "Strathclyde Manning Arrangement" (SMA). Subsequently, the same system was put in place in the Liverpool and London areas, and the general term "Cab Secure Radio" (CSR) was used.


A separate radio channel is used for each area under the control of a particular signalman. Channel changes are normally performed automatically, but lineside signs displaying the channel code are provided at the boundary from one radio zone to the next, and at places where the 'set up' procedure is usually carried out [19.3].

[19.3] Radio Channel Indicator. Status: Obsolescent

The National Radio Network (NRN) originated around 1979. Originally used only by engineering staff on the lineside, by the mid 1980s it was in widespread use in driving cabs. The train driver may use the system to access the railway telephone network from inside the cab. NRN is not a 'secure' system like CSR. The need for lineside electrification telephones ended with the coming of NRN, apart from in tunnels where the NRN will not work. The NRN may be used by the driver to contact the signalman when detained at a signal without a signal post telephone, or where the telephone is not located in a position of safety. At these signals, a sign will be provided stating the telephone number for the signal box concerned (see [9.43 - 9.46]).


Drivers are required to manually set the NRN radio to the correct channel for the area that the train is in and to change channels as the train moves from one radio zone to another. As with CSR, signs are provided at places where the channel needs to be changed, and they show the channel code that applies in the area ahead. A later design of radio channel indicator (in use by 1985), had the diamond shape set against a black background [19.4]. This was also used in relation to CSR.

[19.4] Radio Channel Indicator. Status: Obsolescent

The Radio Electronic Token Block (RETB) signalling system uses a radio network for the transmission of electronic tokens and for verbal communication between train and signalman. The first application was between Dingwall and Kyle of Lochalsh in 1984. Radio channel indicators of the standard design (see [19.4]) were installed on lines with RETB signalling.


For a period, two radio systems were in use over the lines controlled from Inverness (RETB) Signalling Centre. Locomotives were fitted with the original Band 2 radio equipment, while the Class 156 'Sprinter' DMUs, introduced from 1989, used Band 3 equipment. Two different channel codes thus applied over any given section of line. The signs showing the original Band 2 codes were altered to have a yellow background [19.5] to distinguish them from the new Band 3 signs, which had the usual white background. The Band 2 signs were removed c.1992.

[19.5] Band 2 Radio Channel Indicator (RETB). Status: Obsolete

Where CSR is in use, drivers are required to go through a 'set up' procedure, which involves entering a four-digit radio identification number into the system. In most cases, the number shown on the signal identification plate (see Section 9) is used for this purpose, leading zeros being added as necessary to make up the four digits. At some locations, however, a distinct radio identification number needs to be used (because two or more signals in the vicinity may share the same number, albeit with different prefix letters). Where such circumstances apply, the radio identification number is shown on a separate plate termed an 'alias' plate. The alias plate, introduced in 1992, has white figures on a blue background [19.6]. An alias plate may also be provided at a location where no signal exists.

[19.6] Alias Plate. Status: Current Click Here for Photo

In 1996, new radio channel indicators were introduced for each of the three radio systems then in use. The new signs, rectangular in shape, bear the initials of the radio system to which they apply [19.7 - 19.9]. Additionally, the channel indicator for the secure CSR system [19.7] has a different background from signs for the other two non-secure systems.

[19.7] Radio Channel Indicator for CSR. Status: Current Click Here for Photo [19.8] Radio Channel Indicator for NRN. Status: Current [19.9] Radio Channel Indicator for RETB. Status: Current

Although no sign was usually provided at the point where radio coverage ends, a CSR termination board [19.10] was installed on the Grain branch and an NRN termination board [19.11] was installed at Barking. Note that the NRN termination board at Barking has the wrong style of background.

[19.10] CSR Termination Board. Status Uncertain [19.11] NRN Termination Board. Status Uncertain Click Here for Photo

In North Kent, a non-standard form of alias plate with a white background and the letters "CSR" [19.12] was used instead of the standard type with a blue background (see [19.6]).

[19.12] Non-standard Alias Plate. Status Uncertain