Speech and Telegraph Network of the UKWMO in ERA 2

These two maps depict the two core networks but do not show the links between the two networks from the RGHQ to its UKWMO Group Control neither do they include links down to county controls or Armed Forces Headquarters ( AFHQ ). In the telegraph subsection further down this page, the extent of the network at County level will become apparent.

During this era, the two networks were carried on BT Landlines. The main land lines had radio backup provided by the Home Office Department of Telecommunications ( DTELS ). Both the RGHQ and the UKWMO network used the same radio bearer network known as Radio Network One ( RN1 ) for the backbone and Radio Network Two ( RN2 ) for the spurs to operational buildings.

 

ERA 2 Telephony

The Government Emergency Communications Network (ECN) was introduced during the 1980’s. An extensive automatically switched network replaced the previously fragmented structure which often relied on the public telephone network to connect between the fragments. For the first time Police, Fire, Councils, Royal Observer Corps, Regional Government Headquarters, Armed Forces and Government departments were all connected to the same emergency network. It was managed by British Telecom for the Home Office Telecommunications Branch and operated separately from the normal public telephone communications systems. This provided a trunk dial facility for ECN extensions to call any ECN telephone in any bunker across the whole of the UK.

Installation of the SX2000 switches for the ROC part of the ECN started in July 1988 and was completed by March 1989. The ECN was still in existence many years after the end of the UKWMO and was made ready in 1999, should the millennium bug hit the public telephone network. A letter found on the Internet (http://www.ukresilience.gov.uk/media/ukresilience/assets/060810ecn.pdf) dated 10 August 2006 advises of the decommissioning during the following 12-15 months.

The photograph shows a typical ECN exchange switch cabinet on display at the Hack Green Museum who have placed a guard fence around the unit and removed a door to show the inner cabinets. Two SX2000 exchange cabinets are installed within a strong sealed box hardened against electromagnetic impulse (EMP). The switching network is duplicated to improve fault resilience. The line EMP filters are visible on the outside of the cabinet facing the camera.

When fewer extensions were required such as a District Council control a TSX50 unit was used. The TSX50 has a capacity for up to 160 extensions, 32 exchange lines, 24 private circuits and has its own control console. The telephone instruments could be conventional pulse or loop dial but more often a TX14 featurephone.

The switch would be installed in the Telecoms apparatus room in the bunker. In the office accommodation there would be an operators console to control the extension phones. If the console was not fitted the extensions could operate in 'Night Service' mode. Any extension on the ECN could directly dial any other in the UK.

Details of the TSX50 as used in the public network may be found on this web site www.telephonesuk.co.uk/tsx50.htm. The SX2000 is still in production but has been enhanced since the model featured here was installed as part of the ECN. This seems to describe the ECN version www.britishtelephones.com/sx2000s.htm

ECN Numbering Plan

A uniform numbering plan was adopted across the whole of the UK, allowing any ECN extension to call any other on the system. This facilitated the following arrangement. RGHQ's and UKWMO Group HQ's had 3 digit extension numbers, all other extensions had 4 digit numbers. To call the switchboard operator in your own bunker, key 100.

• Internal Calls
  • To call any extension within your own RGHQ building, key the 3 digit extension number.
  • To call any extension within your own Group HQ building, key the 3 digit extension number.
  • To call any extension within your own Emergency Centre, key the 4 digit extension number.
• External Calls.
  • To call a UKWMO Group, key the 3 digit group code followed by the 3 digit extension number. The group code is created by adding a 6 in front of group number; 608 = Coventry No.8, 612 = Bristol No.12
  • To call a RGHQ, key the 3 digit regional code followed by the 3 digit extension number. The Regional code is created by adding 5 in front of the RGHQ number; 531 = Skendleby 3.1, 592 = Drakelow 9.2
  • To call any County Council or District Council Emergency centre, key the 3 digit regional code followed by the 4 digit extension number. This Regional code is the same one for the RGHQ it comes under.

County Councils were allocated 100 extensions maximum per Emergency Centre. The first digit for every council was a 7. Within any one RGHQ, the second digit (x), starting from 0, was obtained by listing the counties alphabetically and assigning two digits per county, first one for the main and the second the standby emergency centre. The last two digits identified one of 100 extensions within that centre. The switchboard would always be 7x00. To make it easy to contact generic functions in any council some numbers were predefined, so for example the County Controller would be 7x01. Scientific Advisers 7x04.

The Three councils under the control of Hertford RGHQ 4.2 would number their extensions as follows: Bedfordshire Main 7000 - 7099; Bedfordshire Standby 7100 - 7199; Essex Main 7200-7299; Essex Standby 7300 - 7399; Hertfordshire Main 7400 - 7499; Hertfordshire Standby 7500 - 7599; This numbering scheme created the full national number on the ECN for Essex Standby Centre's switchboard as 542 7300

District Councils Emergency centre ECN numbers started with a 4. Each was only allocated 25 ECN extension numbers. The lowest number at each control was the incoming number for the switchboard. The numbering increments down the list of centres listed in Alphabetical order by County, District. 4000 - 24; 4025 - 49; 4050 - 74; 4075 - 99; 4100 - 24; 4125 - 49; 4150 - 74; etc for as many District centres as there were in each RGHQ Zone. Again a series of extension numbers were reserved for generic functions, but with 25 extensions it became a little more complicated, Scientific Advisers would be one of 4x04, 4x29, 4x54, 4x79 according to the first number in the block of 25. The national ECN number for the Dacorum District Council (Hemel Hempstead, Hertfordshire) emergency centre switchboard would have been 542 4475, as this being in the third county in the RGHQ 42 list there were 19 other centres before it, in total taking up the 4000 - 4474 range.

 

ERA 2 Telegraph Switch

Modern store and forward automatic switches similar to those in the civilian world replaced the old torn tape telegraph centres. All messages have a header that the switch recognises, the header contains addressing information. The data switch is programmed with a routing table that determines for any particular destination which outgoing link should be used for the message. It could be the message is destined for a location where this switch doesn't have a direct link in this case the routing table contains a link to an tandem point. Messages are stored in the switch in a queue and sent when the link becomes free. The importance of the message governs where it is in the queue. This was exactly what happened in a torn tape centre except now there is no human intervention other than to pre-program the routing table.

After an initial trial in Dundee ROC Group Headquarters the rollout of the 'Case MSX' message switch started at Maidstone and was completed with Belfast in June 1985. I have no detailed information about the RGHQ switch rollout. The MSX switch worked with Visual display units and modern electronic teleprinters similar to the Puma shown here. These were much quicker and easier to use than the old mechanical teleprinters, paper tape perforators and torn tape centres used in the previous era.

Outing messages were prepared using a Visual Display Unit (VDU) and sent to the destination, a local copy could be printed on the journal printer. The VDU could also perform commands on the switching system too such as redirecting failed messages, adding and deleting routing codes. Incoming messages were printed onto paper using an electronic printer.

The 'Case MSX' telegraph switch was used in the RGHQ and UKWMO Control bunkers. In County Council Controls a smaller switch was installed, the 'Autex 1600 Telex Manager' with a maximum of 24 ports. As a backup to this was a 'Autex 100 Telex Manager' with only 5 ports and 128 Kilobyte of memory that allowed a very minimum service to be maintained in the event of a failure of the main switch. At District Council controls the 'Autex 100 Telex Manager' had only 4 ports and 64 Kilobytes of memory. County Police headquarters also had an Autex 100 connected into the Civil Defence network via the County Main or Standby control.

Each node within the RGHQ & UKWMO telegraph network was allocated a short code used in the message header to indicate the desired recipient(s). The message switches examine the destination code in the message and routed it to a port obtained by consulting a directory held within the switch's memory. As each node is only connected to a limited number of nearby nodes it is necessary to route the message via a number of switches to send it to a node that is not directly connected. If the data link land line or radio circuit connected to a port became faulty or was destroyed by enemy action the system operator could divert all traffic from that port onto another working port and the messages would now route over a different path to find the destination.

The table shows a few examples of the Telegraph Network destination codes. All the UKWMO Group Controls had a suffix of 'WM' added to their Royal Observer Corp location three character character code, e.g. 'BEDWM' for Bedford or for the five Sector Headquarters an abbreviation of the Sector name, the METropolitan Sector at Horsham 'METWM'.

Regional headquarters destination codes were three characters made up from the the RGHQ number. Armed Forces Headquarters in each Region used a five character code starting with 'RBD', for example Region 4 'RBDPKT'. County controls had an identity made up of a three letter County code e.g. Gwent 'GWE' suffixed with 'MN' for the County Main Control and 'SB' for the County Standby Control. In counties with District controls, these controls used the county code with a two letter suffix in the form of an abbreviation of the District Council name. Districts in Gwent, Monmouth 'GWEMO'; Newport 'GWENO'. Police HQ routing codes followed a similar convention with a 'PO' suffix or 'FB' for Fire Brigade.

 

ERA 2 County Telegraph Network

This drawing centered on Oxfordshire, shows the connections between the various controls and two adjacent Counties. The message routing codes are shown (in Green) for each node. The RGHQ at Basingstoke (RGHQ 6.2) also had many links omitted for clarity to the main and standby controls in Hampshire and the Isle of White, also to Winchester UKWMO Group Headquarters and AFHQ in for Region 6.

RGHQ 62 at Basingstoke was connected into the RGHQ core network with links to RGHQ's at Hertford: 4.2, Kelvedon Hatch: 5.1, Crowborough: 6.1, Chilmark 7.1, Swynnerton: 9.1

The UKWMO Oxford Group Headquarters at the ROC No 3 Group at Cowley had links into the UKWMO core network with connections to Bedford, Bristol, Coventry, Horsham, Shrewsbury, Winchester and Yeovil.

Using this example of a small area it can be seen that the Civil Defence telegraph network in the UK was very extensive. Telegraph messages could be passed between any node throughout the countrywide network. Should links within the network be broken due to enemy action the messages could be rerouted via working sections.

A standardised configuration of ports on the Autex 1600 switches at County Main and County Standby control was adopted as shown in the table. Flexibilty in the use of ports 10 to 22 allowed for Counties with a number of District controls. Note the connection to the RGHQ or Scottish Zone, has two data links, one by landline and the other over the radio circuit. Both these links employed S+DX on the telephony circuit between the two bunkers.

 

ERA 2 Radio backup to landlines

During the later part of the 1980’s changes to the radio frequencies used for emergency services heralded the introduction of a new radio scheme for the UKWMO. The new Radio Network moved away from the older single channel per carrier at VHF and UHF frequencies towards the Microwaves where a higher bandwidth was available to enable lots of circuits to be carried on the same radio channel.

Radio Frequency Allocations

During the 1980's there were lots of changes to the Home Office frequency allocations for Emergency Services. The 146-148MHz and 154-156MHz frequency assignment was increased by the addition of 143.000-144.000MHz paired with 152.000-153.000MHz. The 147.000-147.300MHz paired with 155.000-155.300MHz sub band previously used for the ROC was withdrawn and reassigned for Emergency Service use. The exclusive Civil Defence band 168.325-168.800MHz paired with 174.025-174.500MHz was retained. The UHF frequencies 452.000-452.300MHz paired with 466.000-466.300MHz and 455.825-456.000MHz paired with 469.875-470MHz continued to be used.

According to the tables supplied by the Dept. of Trade and Industry in 1985, the following microwave bands are available for use by the emergency services including the UKWMO. ‡ This band was replaced and is now part of the GSM allocation. Two additional 8 MHz bands have been added sometime before 2002 at 1677-1685MHz and 1790-1798MHz.

Extract from 'UK Table of Frequency Allocations' 1985

Band Limits MHz	Bandwidth MHz	Allocation
1668-1670	2	HO/SE (for the fixed service)
1698-1700	2	HO/SE (for the fixed service)
1807.5–1815.5	8	HO/SE (fixed service)‡
2302–2310	8	HO/SE (for the fixed service)
10250-10270	20	HO/SE (for the fixed and mobile services)
10360-10400	20	HO/SE (for the fixed and mobile services)

'Home Office' or 'Scottish Executive' abbreviated HO/SE

DoTI frequency allocation table 1985 shows 862-864MHz and 889-890MHz bands, I have no information about their use. The Radio Authority, document RA365 dated Feb 2000 also shows an allocations at 460.500-460.750 MHz, 462.500-462.750 MHz, these too may have been used for Civil Defence UHF multiplexes but confirmation is required.

RN1 and RN2 Structure

The new national radio network consisted of a backbone designated RN1 and spurs to users bunkers designated as RN2. RN1 was a high capacity radio network where lots of individual circuits could be combined on to one radio system operating at microwave frequencies. RN2 was similar but with lower capacities and operated at both UHF and microwave frequencies. Both RN1 and RN2 used speech multiplex a technique also used on landlines to cram a number of speech circuits onto one bearer. Speech Multiplex is described in a separate topic.

This diagram show the extent of the RN1 spine network passing between hilltop radio sites and including six RGHQ bunkers and two UKWMO Group HQ's too. All the other locations such RGHQ's and Group Headquarter and Council bunkers were connected into the spine with the RN2 network. The individual circuits are cross connected between multiplexes at the hilltop sites in order to achieve a point to point link spanning between bunkers. To allow circuits to take a diverse routing, some of the multiplexed links in RN1 were formed into a ring allowing some circuits to route in one direction around the ring and others in the opposite direction. Multiplexes with 8, 12 and 24 channels were be used, depending on the capacity needed in that part of the network.

The RN1 network diagram is only a small part of the story and doesn't show which circuits were carried on individual RN1 links. The RN2 network must have been quite extensive considering how many locations had to be connected but I don't have any detailed information. Probably the majority of Home Office hilltop sites ( Green spots on the diagram) were used to convey RN2 links to bunkers. The Green spots are masts identified from various web based sources and HO Circular 155 of 1963.

It has been suggested that the RN1 / RN2 radio backup to line circuits never actually carried traffic. Apparently the interconnection of multiplex channels at hilltop sites was never completed. I would be interested in feedback to know whether this was a local problem or the national picture.

Aerial Systems

The spine of the UKWMO Radio Network RN1 was carried on microwave shrouded yagi aerials as they were thought to be more resilient to the effects of a nuclear blast pressure wave than the much larger dish aerials. They operated on frequencies in the 1-2GHz bands allocated to the Home Office where a fairly sizable dish would have been necessary to achieve the same aerial gain.

The RN2 access spurs to the control bunkers from the RN1 spine used either single channel per carrier or multiplexed UHF links according to the capacity needed. Local Council bunker were candidates for single channel per carrier links at UHF or 1+1 carrier systems. The UKWMO Group Controls and RGHQ, where there were more circuits terminating, would be served by a multiplexed link. Whether they be for single channel or multiplexed systems a UHF link would use a 12 element yagi similar to the one shown on the right fixed to my Local Council premises.

The Microwave Dish aerial sometimes called a Microwave Drum Antenna, contain a circular parabolic reflector with a centre mounted feed, similar to a Satellite TV aerial encased in a protective drum with a plastic or fabric front to allow the radio signal to pass while keeping the weather out.

Sizes of dishes can vary from a few tens of centimetres for the 38GHz bands, often used on mobile phone masts to 4 metres that were common on the BT national network at one time, operating in the 2-5GHz region. The larger sizes that would have been required for RN1 frequencies would have presented quite a wind loading, yet alone a blast wave.

Radio Link Equipment

This photograph shows a Plessey PRD1100 with the Orange front panels on the left serving one RN2 link. The slightly taller racks on the right house two Pye L700 microwave links and their associated analogue speech multiplex cards. Most sites like this had two L700 assemblies providing a link in each direction on the RN1 backbone. Many of the black L700 front panels have been removed for commissioning.

The Pye L700 formed the backbone RN1 links functioning in the 1.6GHz band it delivered a baseband signal to a separate multiplex which could provide 8, 12 or 24 Multiplexed speech channels.

The Plessey PRD 1100 Multiplex for the RN2 network worked in the UHF bands and used mainly the 8 channel variant but some 12 channel units existed too. This MUX used UHF frequencies of 452.000-452.300MHz paired with 466.000-466.300MHz and 455.825-456.000MHz paired with 469.875-470MHz for the RN2 network.

The regulations only allowed 500KHz bandwidth for the 8 Channel systems on UHF and 800KHz for the 12 and 24 channel systems in the low microwave bands. So to accommodate this the deviation of the transmitter had to be altered which is why 12 channel voice channels sounded far better than the 8 and 24 Channel systems. However to complicate matters even further for the technician some 12 channel systems had to be compressed to use 500KHz deviation.