The UKWMO Speech and Telegraph Network mid-1980's-1992
This topic describes the changes to the original communications network that took place during the mid-eighties. By this time the effects of Electro-Magnetic Pulse induced by atomic weapons were understood and reflected into the design.
The Final Speech and Telegraph Network of the UKWMO
Inter-ROC Group HQ Network
Reproduced from Ordnance Survey map data by permission of the Ordnance Survey © Crown Copyright 2001.
Reproduced from Ordnance Survey map data by permission of the Ordnance Survey © Crown Copyright 2001.
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 Directorate 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 E.C.N.
ECN Switch exhibited at Hack Green
The Government Emergency Communications Network (ECN) was introduced during the 1980ís. An extensive automatically switched network replaced the previous Government Control Network (GCN) 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 UKWMO part of the ECN started in July 1988 and was completed by March 1989. The ECN continued to be used after the closure of the RGHQ's, see the next topic on this page. The core network was based around switches located in the Regional Government Headquarters (RGHQ).
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 controls a TSX50 unit was used. The TSX50 has a capacity for up to 80 extensions, 24 exchange lines, 8 private circuits and has its own control console. The telephone instruments could be conventional desk or wall telephone (LD or MF4) as well as the 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 are allocated 100 four digit ECN extension numbers per Emergency Centre. The first digit being a 7, then within any one RGHQ zone, the second digit (x), starting from 0, is obtained by listing the counties alphabetically and assigning firstly the main and then the standby emergency 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.
District Councils are allocated 25 four digit ECN extension numbers per Emergency Centre. The first digit being a 4, then within any one RGHQ zone, the remaining three digits (xyz), starting from 000, are increment by 25 for each centre in an alphabetical list by County and District. e.g. 4000 - 24; 4025 - 49; 4050 - 74; 4075 - 99; 4100 - 24; etc. The lowest number at each emergency centre is the incoming number for the switchboard. Again a series of extension numbers were reserved for generic functions, but with a 25 number block 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 twenty five.
The paragraphs above describe the numbering plan, the actual number of extension telephones fitted per emergency centre would be dictated by local circumstances and most likely well short of the ultimate capacity of the telephone switch.
Click to Show - The Detailed ECN Numbering Plan for Region 3
Home Defence Region 3, ECN Number Ranges
RGHQ 31 Skendleby 531 100-299
Derbyshire Main Emergency Centre 531 7000-99
Derbyshire Standy Emergency Centre 531 7100-99
Lincolnshire Main Emergency Centre 531 7200-99
Lincolnshire Standy Emergency Centre 531 7300-99
Nottinghamshire Main Emergency Centre 531 7400-99
Nottinghamshire Standy Emergency Centre 531 7500-99
Amber Valley District Council 531 4000-24
Bolsover District Council 531 4025-49
Chesterfield District Council 531 4050-74
Dales District Council 531 4075-99
Derby City Council 531 4100-24
Erewash District Council 531 4125-49
High Peak District 531 4150-74
North East Derbyshire District Council 531 4175-99
South Derbyshire 531 4200-24
Boston District Council 531 4225-49
East Lindsey District Council 531 4250-74
Lincoln City District Council 531 4275-99
North Kesteven District Council 531 4300-24
South Holland District Council 531 4325-49
South Kesteven District Council 531 4350-74
West Lindsay District Council 531 4375-99
Ashfield District Council 531 4400-24
Bassetlaw District Council 531 4425-49
Broxtowe District Council 531 4450-74
Gedling District Council 531 4475-99
Mansfield District Council 531 4500-24
Newark + Sherwood District Council 531 4525-49
Nottingham City Council 531 4550-74
Rushcliffe District Council 531 4575-99
RGHQ 32 Loughborough 532 100-299
Leicestershire Main Emergency Centre 532 7000-99
Leicestershire Standy Emergency Centre 532 7100-99
Northamptonshire Main Emergency Centre 532 7200-99
Northamptonshire Standy Emergency Centre 532 7300-99
Blaby District Council 532 4000-24
Charnwood District Council 532 4025-49
Harborough District Council 532 4050-74
Hinkley + Bosworth District Council 532 4075-99
Leicester City 532 4100-24
Melton District Council 532 4125-49
North West Leicestershire DC 532 4150-74
Oadby & Wigston District Council 532 4175-99
Rutland District Council 532 4200-24
Corby District Council 532 4225-49
Daventry District Council 532 4250-74
East Northamptonshire District Council 532 4275-99
Kettering District Council 532 4300-24
Northampton District Council 532 4325-49
South Northamptonshire District Council 532 4350-74
Wellingborough District Council 532 4375-99
Post Cold War use of the ECN
Post RGHQ Network
At the end of the Cold War, the network continued to exist for another fifteen years or so. In 1999 it was made fully ready should the millennium bug hit, disrupting the public telephone network. A government letter dated 10 August 2006, advises of the decommissioning during the following 12-15 months. This would suggest final closure around the end of 2008. A Cabinet Office Freedom of Information request FOI320131 quotes an earlier decommissioning date of 2005.
After the 1992 closure of RGHQ's the network was rearranged, moving top tier switches to new locations around the UK and linking them together. The locations and the former RGHQ zones, were Easingwold , Durham , Ryton in Dunsmore [31, 32, 91, 92], Halesworth [41, 42] Queen Anne's Gate , Ashford , Bramshill / Basingstoke , Yeovil [71, 72], Cwmbran [81, 82], Bruche / Warrington [101, 102].
SubBrit states the Yeovil switch node site was located in the former ROC Group HQ which closed 31.12.1973 as part of the rationalisation plan.
Top tier nodes acted as tandems as only adjacent nodes were directly connected, shown by the black lines in this diagram. The numbering scheme for the counties remained unchanged from the cold war period.
For the first time, a bridge was introduced giving access to the ECN from the public fixed and mobile network. A national number allocated to each top tier switch could be dialled, when ringing tone changed to dialling tone, a pass code was entered, if this was correct, dial tone returned and the required full ECN number was keyed in. There was also a bridge from most top tier nodes into the Army Telephone Network (ATN).
ERA 2 - MSX Telegraph Switch, at UKWMO Groups and RGHQ's
Message Switch Process
MSX Message Switch Cabinets
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 as well as the text of the message, the header contains a routing code or addressing information that the switch recognises.
The data switch is programmed with a routing table that determines for any particular routing code which of it's outgoing ports to send the message. A port can be either local printer or a Visual Display Unit (VDU). Other ports connect to other message switches in the network via landline or radio link.
If the message is destined for a location without a direct link, the routing table contains a ports who's link goes to a tandem message switch. It may be necessary to pass the message through a number of tandem switches before it reaches the destination. In each switch, messages are stored in a queue and sent when the outgoing port becomes free. The importance of the message governs where it is in this queue. This replicates 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 UKWMO 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 ( VDU ) 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.
Outgoing messages were prepared using a VDU and sent to the destination, a local copy could be printed on the journal printer. The VDU operator could also perform management 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.
Each function within the RGHQ & UKWMO telegraph network was allocated a short address code used in the message header to indicate the desired recipient(s). The message switches examine the destination address code in the message header and route it to a port obtained by consulting a directory held within the switch's memory. As each node is connected to a limited number of nearby nodes it is often necessary to route messages via a number of tandem nodes to get to the desired destination. If the data link land line or radio circuit connected to a port becomes faulty or is destroyed by enemy action the system operator can divert all traffic from that port onto another working port and the messages will find a different path to find the destination.
One routing code can be used to broadcast a message to a number of destinations. It was clever stuff for 1980 and another 20 years would pass before EMAIL became commonplace - its what we know as an address list. One particular printer or VDU may be the destination for many routing codes. In EMAIL terms - having many email addresses drop into one Inbox.
Example of Address Codes
|| ||Commandant||ROCWM |
|RGHQ Sites||RGHQ 2.1|
| ||RGHQ 2.2|
STBY: Kings Lynn
| ||RGHQ 9.2|
||District Council||Milton Keynes|
||Emergency Svce||Kent Police|
The table shows a few examples of the Telegraph Network destination routing codes. A list of MSX codes are itemised in the Royal Observer Corp, Standard Operating Procedures, Annex AM. 'Identification Codes (Address of Units) including Multi-Address Codes'. Below is a breakdown of the format of codes used
Regional headquarters destination codes in England and Wales were three numbers made by padding the RGHQ number with zeros. Scotland and Northern Ireland had a longer code.
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. The Admin group's address is 'ROC' and the group number e.g. 'ROC07' for Bedford. The operational five Sector Headquarters an abbreviation of the Sector name, the METropolitan Sector at Horsham 'METWM'.
In addition to direct point to point codes, special broadcast codes were allocated to allow a single message to be sent at once to all recipients. For example, addressing a message to MAMT2 would deliver it to all Groups, NRC and Local Authority Emergency Centres in the Metropolitan sector area.
Example of Broadcast Codes
| ||Sector Control to all Groups in their sector |
|MACL1||Caledonian Sector |
|MAMT1||Metropolitan Sector |
|MAMD1||Midland Sector |
|MASU1||Southern Sector |
|MAWS1||Western Sector |
| ||Sector Control to all Groups, NRC's and Customers |
in their sector
|MACL2||Caledonian Sector |
|MAMT2||Metropolitan Sector |
|MAMD2||Midland Sector |
|MASU2||Southern Sector |
|MAWS2||Western Sector |
| ||Sector Control to all other Sector controls |
|MACL3||From CAL (Caledonian) to MET MID SOU WES |
|MAMT3||From MET (Metropolitan) to CAL MID SOU WES |
|MAMD3||From MID (Midland) to CAL MET SOU WES |
|MASU3||From SOU (Southern) to CAL MET MID WES |
|MAWS3||From WES (Western) to CAL MET MID SOU |
| ||Broadcast BB (Bomb Burst) Messages, BBxxx |
one per Group
|BBCOV||From Coventry |
|BBEXE||From Exeter |
| ||Broadcast TT (Fallout Threat) Messages, TTyyy |
one per Sector
|TTSOU||From Southern Sector |
|TTWES||From Western Sector |
During the attack and post-attack period, Group and Sector controls would originate many routine messages in a fixed format. Some message formats being copies of ROC's paper forms containing vital information. To facilitate sending these routine messages, broadcast codes in the format xxYYY were created, where xx was the form code and YYY the originating group or sector. For example BB (bomb burst) messages originate from Groups while TT (fallout threat) messages originate from Sectors. Two examples are shown in the Broadcast Code table.
Local Authority Emergency 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, addressed as 'GWEMN' and GWESB' respectively. 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'. County Police Headquarters routing codes followed a similar convention with a 'PO' suffix following the county code, 'GWEPO' for Gwent Police. County Fire Brigade Headquarters used a 'FB' suffix, 'GWEFB' for Gwent Fire.
The U.K Armed Forces were linked into the UKWMO / RGHQ network, all their routing codes begin 'RBD' these are a sub-set of military routing codes used by all three services and our allies, all those based in the UK are in the format RBDxxx. This is further explained in the topic Communications / To Military linked from further reading or the tabs at the top of this age.
Within each Home Defence Region, one Armed Forces Headquarters (AFHQ) served the Region and was linked into both the RGHQ and UKWMO telegraph networks and possessed its own routing code. In the case of Region 2 the code for its AFHQ is RBDAPM. The two RGHQs in each Region each contained a co-located Military liaison office, as this military were tasked in supporting the counties in a post-strike recovery phase. Each Military Liaison office having its own separate routing code from that used by the Civilian part of the RGHQ. At Shipton the Civilian routing address is 021 and its military counterpart RBDPAP.
ERA 2 County Telegraph Network
The 'Case MSX' telegraph switches were used in the RGHQ and UKWMO Control bunkers, but in Local Authority Emergency Controls (LAEC) a smaller switch, the 'Autex 1600 Telex Manager' with a maximum of 24 ports were used instead. The installation consisted of three Siemens PT85 printers and two Zentec ADM3E Visual Display Unit (VDU).
As the Autex 1600 has only a single processor, a backup 'Autex 100 Telex Manager' with just 5 ports and 128 Kilobyte of memory, allowed a very minimum service to be maintained in the event of a failure of the main Autex 1600 switch. Only two external links are provided to the backup Autex 100, one to the RGHQ and the other linking the Main LAEC to the Standby LAEC. One VDU and two printers are supported by the backup switch.
At District Council controls and County Police headquarters were fitted with a 'Autex 100 Telex Manager' having only 4 ports and 64 Kilobytes of memory, like the one shown in the gallery. These small units connected into the national telegraph network via the switches in the Council Main and Standby controls. The unit has two Single Channel Voice Frequency Telegraph (SCVFT) modem cards for the external line connections to the Main and Standby LAEC, the rear panel houses D-Type connectors for a single MT80 printer and a dual purpose Zentec ADM3E. This VDU would be used to prepare outgoing messages as well as manage the switch's supervisory functions.
Mannesman Tally MT80
Standardised Autex 1600
|00 ||Journal Printer |
|01 ||Incoming Message Printer A |
|02 ||Incoming Message Printer B |
|03 ||VDU A |
|04 ||VDU B (spare) |
|05 ||Line data link to UKWMO Group Control |
|06 ||Line data link to RGHQ/ZONE |
|07 ||Radio data link to RGHQ/ZONE |
|08 ||Line data link between Main & Standby |
|09 ||Line data link to Police HQ |
|Line data links to Districts |
as required by the Local Authority
to a maximum of 13 District controls
|Input from a |
portable Disk Drive
A standardised configuration of ports on the Autex 1600 switches at County Main and County Standby control was adopted as shown in the table. Flexibility 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.
Similarly, the AUTEX 100 switches used at District level and Police HQ's also had a standardised port allocation for their four ports to ease with network administration.
Civil Defence Telegraph Network at County Level
This drawing centred 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.
ERA 2 Radio Networks RN1, RN2 and RN4
During the later part of the 1980ís the emergency services were required to change their main operating frequencies to comply new World Administrative Radio Council ( WARC ) rules. This heralded the introduction of a new radio scheme for the UKWMO and RGHQ network. This network moved away from the older single circuit per carrier at VHF and UHF frequencies towards a Microwave backbone where a higher bandwidth enabled many circuits to be carried on the same radio carrier.
Radio Frequency Allocations
The WARC changes removed the Home Office frequency allocations for Emergency Services at 97.6-102.2MHz and these moved into the existing 146-148MHz and 154-156MHz frequency assignment, which was increased by the addition of 143.000-144.000MHz and 152.000-153.000MHz. The sub-bands 147.000-147.300MHz paired with 155.000-155.300MHz previously used for the ROC Network were withdrawn and reassigned for Emergency Service use. The exclusive Civil Defence band 168.325-168.800MHz paired with 174.025-174.500MHz was retained for use by RN4. At the same time the Emergency Services UHF allocations were expanded in size by adding the 450-451MHz to the 451-453MHz band and adding 464-465MHz to the 465-467MHz band. The UHF frequencies used for RGHQ links within the Emergency Service allocation 452.000-452.225MHz paired with 466.000-466.225MHz remained in use and the exclusive 455.875-456.000MHz paired with 469.875-470.000MHz continued to be used.
Click to Show - The Detailed UHF Channel Plan
UHF Frequencies allocated for UKWMO and RGHQ Network
LOWER CHANNELS UPPER CHANNELS
452.000 466.000 455.8875 469.8875
452.025 466.025 455.9125 469.9125
452.050 466.050 455.9375 469.9375
452.075 466.075 455.9625 469.9625
452.100 466.100 455.9875 469.9875
Two frequency assignments, 30 Megahertz apart and 2 Megahertz wide at 1668-1670 MHz and 1698-1700 MHz were allocated for RN1 and RN2 high capacity links as they needed a greater bandwidth than was available on the UHF channels.
RN1 and RN2 Structure
RN1 Network Spine
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 capacity links to RGHQ or UKWMO ROC Group HQ operating at either UHF and microwave frequencies. Smaller bunkers, such as Local Authority Emergency Centres had one or more RN2 single channel links. Both RN1 and RN2 high capacity links used Frequency Division 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 have very little specific information on the RN2 part of the network. 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 spine 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.
RN2 Network Examples
The RN2 extension from RN1 sites consisted of a minority of high capacity links to the ROC UKWMO headquarters and a few RGHQ that weren't RN1 sites in their own right, and a majority of single channel links backing up emergency centre's landlines to their RGHQ. In municipal counties and London, RN2 radio links backed up the landlines between the county and borough emergency centres. The gallery shows part of the London area RN2 and RN2 radiating out of Brown Clee in the Midlands.
More information or examples of the RN2 network would be most welcome.
RN4 Group to Master Post Radio
The network designated as RN4 comprised of the ROC Post radios and the radio at the group control centre operating in the 80 MHz band. Due to the large geographical area covered by a Group HQ the more distant posts may not be able communicate directly with the HQ. The RN4 network also included hilltop sites linked at VHF to the headquarters.
The RN4 radio scheme is described in detail in a more appropriate topic Communications / ROC Post ERA 2
Shrouded Yagi Aerial for RN1
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 1.2 metre dish would have been necessary to achieve a similar aerial gain. Dishes of this size or larger would have been likely to suffer blast damage from a nuclear blast therefore the shrouded yagi offering less wind resistance was the option chosen for this frequency range.
UHF 12 Element Yagi ( 450-470MHz )
Most RN2 access spurs from the RN1 spine to the control bunkers used either single channel per carrier or multiplexed UHF links according to the quantity of circuits needed. UKWMO Group Controls and RGHQ, warranted a UHF multiplexed link due to the number of circuits terminating there.
Some higher capacity RN2 links, such as the one to Hack Green RGHQ from Old Pale used the same frequency band as their RN1 counterparts.
Local Council bunkers were candidates for single channel per UHF carrier links. A UHF link whether it be for single channel or a multiplexed system would use a 12 element yagi similar to the one shown on the right fixed to my local council premises.
Radio Link Equipment
Typical RN1 site with RN2 Spur
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. Looking at the network spine drawing further up this page it can be seen that most sites like this one 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, 24 or 36 Multiplexed speech channels. To fit the signal bandwidth into the channel spacing in these bands the peak deviation on RN1 was adjusted to 28.3, 49.5, 70.7 and 35.4 kHz respectively
Pye F496 for RN2
The Plessey PRD 1100 Multiplex for the RN2 network worked in the UHF bands and carried 8 or 12 multiplexed speech channels. The RN2 network used UHF frequencies of 452.000-452.275MHz paired with 466.000-466.275MHz and an exclusive band at 455.875-456.000MHz paired with 469.875-470.000 MHz. The first band pair was shared with emergency services communications having channels spaced 25kHz apart. To fit in with this spacing, the PRD1100 capability for 12 channel was reduced to 8 channels, and still required two channels bandwidth when operating with 14.2kHz peak deviation.
When a single RN2 radio channel is required, to link to a hilltop to pick up the RN1 network or to another bunker. One or more Pye F496 wall mounted radios were used. The F496 is normally mains powered but has the ability to have a standby battery supply too.
These radios are most likely to be found at county emergency centres, perhaps backing up the landline to RGHQ or to its district council bunkers.
RN3 Onsite Security
The onsite security at Belfast UKWMO Group Headquarters, consisted of a pair of Pye PF9 Pocketfones working into a Storno CQM 5662 Basestation, running 5 watts into a Jaybeam UHF folder dipole. These worked on Home Office Channel 13 (451.475 Tx / Rx) allowing all three units to communicate with one another.
As well as Belfast No.31 Group, RN3 was installed at Maidstone No.1 Group, Shrewsbury No.16 Group, Preston No.21 Sector, Carlisle No.22 Group. Many others had it fitted too, although it is confirmed that Coventry No.8 didn't have RN3.
It would be interesting to know if a similar arrangements were used at Regional Government Headquarters too ?