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Section 19: Radio Signs

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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 form of radio system. The original analogue systems have been supplanted by newer digital systems.

The provision of an in-cab radio system was a specific safety requirement to enable 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 original "DOO Radio" was introduced c.1981 on the lines between London King's Cross and Welwyn Garden City / Hertford North (Eastern Region), and between London St. Pancras and Bedford (London Midland Region). A development of the DOO Radio system was implemented in the Glasgow area in 1986, this being referred to originally as the "Strathclyde Manning Arrangement" (SMA). Subsequently, the same system was established in the Liverpool and London areas, and it became known as "Cab Secure Radio" (CSR). The system was secure, in that the driver and signalman could communicate on a one-to-one basis and not be heard by anyone else. The signalman had the facility to transmit a general message to all drivers in a particular area.

A different radio channel applied to each area under the control of a particular signalman. Channel changes were normally performed automatically, although lineside signs were provided at the boundary from one radio zone to the next and at places where the 'set up' procedure was usually carried out. The original channel indicator signs comprised a white diamond-shaped board with the appropriate channel code in the centre [19.1].

[19.1] Radio Channel Indicator.
Area: All Areas   Usage: High   Status: Historical

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 [19.2 & 19.3]. When the Regional Operations Manager travelled over the Aberdeen to Inverness 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 this did not happen.

[19.2] Channel Change Board.
Area: Dingwall - Kyle of Lochalsh   Usage: Low   Status: Historical
[19.3] Channel Change Board. Click Here for Photo
Area: Aberdeen - Inverness   Usage: Low   Status: Historical

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. Train drivers could use the system to access the railway telephone network from inside the cab. NRN was 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 would not work. The NRN could be used by the driver to contact the signalman when detained at a signal without a signal post telephone or where the telephone was not located in a position of safety. At these signals, a sign was provided stating the telephone number for the signal box concerned (see [9.48 - 9.51]).

Drivers were required to manually set the NRN radio to the correct channel for the area that the train was in and to change channels as the train moved from one radio zone to another. As with CSR, signs were provided at places where the channel needed to be changed, and they showed the channel code that applied in the area ahead. A later design of radio channel indicator (in use by 1985) had the white diamond set against a black background with semicircular edges at the top and bottom [19.4]. This form of indicator was also used for displaying CSR channels.

[19.4] Radio Channel Indicator.
Area: All Areas   Usage: High   Status: Historical

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).
Area: Far North Lines   Usage: Medium   Status: Historical

Where CSR was in use, drivers were required to go through a 'set up' procedure, which involved entering a four-digit radio identification number into the system. In most cases, the number shown on the signal identification plate (see Section 9) was 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 had to be used (because two or more signals in the vicinity may share the same number, albeit with different prefix letters). Where such circumstances applied, the radio identification number was shown on a separate plate, termed an 'alias' plate. The alias plate, introduced in 1992, had 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. Click Here for Photo
Area: All Areas   Usage: High   Status: Historical

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

[19.7] Radio Channel Indicator for CSR. Click Here for Photo
Area: All Areas   Usage: High   Status: Historical
[19.8] Radio Channel Indicator for NRN.
Area: All Areas   Usage: High   Status: Historical
[19.9] Radio Channel Indicator for RETB.
Area: All Areas   Usage: Medium   Status: Historical

Although no sign was usually provided at the point where radio coverage ended, CSR termination boards [19.10] were installed on the Grain branch and at Bletchley, and an NRN termination board [19.11] was installed at Barking. The termination boards were similar in appearance to the ordinary radio channel indicators, with the addition of a red diagonal cross. Note that the NRN termination board at Barking had the wrong style of background.

[19.10] CSR Termination Board. Click Here for Photo
Area: Various   Usage: Low   Status: Historical
[19.11] NRN Termination Board. Click Here for Photo
Area: Barking   Usage: Low   Status: Historical

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.
Area: North Kent   Usage: Low   Status: Historical