Speech and Telegraph Networks of the UKWMO in ERA 1

Within the UKWMO there were two distinct networks of similar design one for the ROC and the other for the Government. Both networks carried both speech and telegraph messages. At each node the speech circuit would terminate on a telephone switchboard and the telegraph circuit in the message centre. Both networks used British Telecom (BT) landlines and Home Office radio links.

The Royal Observer Corp Network

The Royal Observer Corp (ROC) network connected all the adjacent Group Headquarter. By the use of message centres it was possible to send messages between any two locations even though they were not directly connected.

During the late 1970’s the five Sector Headquarters had sufficient traffic the warrant direct links. Before these additional circuit were added only Preston and Lincoln Sectors were directly connected as they are adjacent so all other inter-sector traffic had to be relayed via another Group.

As far as I know these inter sector links were landlines only without radio standby links.

Regional Government Headquarters Network

The Regional Government Headquarters (RGHQ) had a similar network connecting their adjacent sites together. This network extended upwards to the Central Government Headquarters (CGHQ) in Corsham and downwards to local government. Local council main controls were linked to their RGHQ. Later on council standby controls were included in the RGHQ network. Each RGHQ had a network link to its associated ROC headquarters too.

 

ERA 1 Telephony

From the 1960’s until the communications upgrade in the 1980’s the ROC and RGHQ bunkers had manual switchboards with a mixture of public telephone lines and private circuits for use by the extension telephones in the building.

The small Private Manual Branch Exchange shown here has the capacity of 10 exchange lines and 50 extensions, is of the type used at small control centres, such as those operated by County Councils. The PMBX10+50 was a standard item used on the public network. An extension would have to ask the switchboard operator to ring another extension. For outside calls the operator connected the extension to an exchange line may have dialled the external number too.

The larger multiple position switchboard may have been used on its own as a manually operated switchboard or in conjunction with an automatic switch. The automatic switches of this era were of the electromechanical type. The operator would connect incoming calls. Extensions could usually dial an external number by prefixing it with a nine but some establishments required to operator to connect the call. Calls to other bunkers over private circuits were usually connected by the operator.

The ROC and the RGHQ had their own private networks of landlines and radio links. An extension wishing to call another elsewhere in the network would ask the switchboard operator to connect them. The operator would place the cord into the jack on the switchboard face and operate the 'ring' key. This would call the attention of the distant operator who would ring the distant extension. This could be quite a protracted process as each operator may be dealing other calls. There may be only one or two lines between switchboards so extensions may have to queue to get connected.

Post Office Emergency Network

During the nineteen sixties and the early seventies, long distance calls over 25 miles, were connected by the public telephone operator. In wartime that service would be compromised so the Post Office set up a small network of special switchboards in protected areas of telephone exchanges to maintain a long distance connection for emergency services. This network was known as the Emergency Manual Switchboard Service (EMSS). The EMSS is described in its own topic if you wish to read more.

Although automatic dialling of long distance calls became universal by the end of the seventies the EMSS network was retained throughout the Cold War period. Before the digitalisation of the UK network in the late eighties the automatic long distance dialling network provided no alternative routing of calls should part of the network fail. Therefore it was important to retain a manual network which could adapt to a wartime situation.

ROC Group Headquarters and Regional Government Headquarters had connections into this EMSS network to allow them to speak to people outside their own network. The EMSS could be used should part of their own private network fail.

ERA 1 Torn Tape Telegraph Message Centre

This describes the functioning of a torn tape message switching centre like those used in the UKWMO at Royal Observer Corp (ROC) Headquarters and Regional Government Headquarters (RGHQ) prior to their communications upgrade in the mid 1980's.

Their use was widespread beyond the UKWMO, as a child I recall a conducted tour at the USAF base at Croughton, Oxon. (Possibly 1967) Being shown the tape centre and the new 80-hole punch card system that had just been installed. They gave us a punched card that I kept for many years saying something like 'Welcome to RAF Croughton from the officers and servicemen of Autodin.' Some large companies had their own tape message centre too.

Each ROC Group HQ and each RGHQ had its own message centre. They were connected to a small number of adjacent centres in their own network with a link at each node between the ROC HQ and its RGHQ. The links normally worked over the landline but could be switched to an alternative radio link and would send messages in either direction. Each link had a paper tape reader connected to the 'send' and a paper tape perforator connected to the 'receive'. A teleprinter connected to a tape reader would convert paper tape messages to printed copies. A Teleprinter with a paper tape perforator or a punch unit created outgoing message tapes.

Message Tape

The telegraph network used a 5-bit baudot code sent at 50 baud, which is very slow by today’s standards but suited the mechanical devices it was designed for. The five hole code for each character was punched in a row across the width of a paper tape.

This type of paper tape was used by business telex and small scale use. For message centres it was desirable to have the message printed down the side of the tape to assist the operators in handling the messages. The small piece of paper punched out of the hole known as a chad is undesirable in a message centre. They create disposal problems and tend ingress into mechanisms causing faults. To overcome the problems a chadless tape was used which had a square hole cut on three sides and attached on the other.

Sending a Message

A typist would prepare a message by typing on a punch producing a paper tape or a teleprinter with a tape perforator. The message would start with a header indicating the destination(s) of the message, the message itself and a run out of blank tape. This was torn from the perforator and carried to the tape reader on the link to the desired recipient.

The tape was placed in the reader and the start button pressed. The teleprinter signals would be sent to the distant end, if that were a teleprinter the message would be printed on the paper roll. If it were another message centre, the signals would cause the associated tape perforator to reproduce the sent message tape. If the message were a broadcast it would be transferred to the next reader and sent again to that destination.

Receiving a message

An incoming message would be perforated onto paper tape and a lamp illuminated to indicate the arrival of the message. The operator would tear the tape from the punch and visually inspect the header. The tape would be transferred to a reader associated with a local teleprinter. This would print the message on a paper roll. The paper was torn from the machine and placed in the out-tray to be taken to the recipient.

Indirect and through messages

If the originating message was destined for recipient at a location without a direct link, or the direct link was faulty or destroyed by enemy action the tape would be sent to another message centre. On receipt the operator would inspect the header and see that it was not for their centre. If the message were for a destination which centre had a working direct link the tape would be placed on the reader of that link and sent. Otherwise it would be sent to another centre with a possible link. The choice of alternative centres is known as the 'routing'.

Flexibility and Economy

A torn tape message centre was a very efficient way to achieve full message routing throughout a network of locations without having to connect every one to the others. It is very flexible too as the operators can use their intelligence to work around a fault or non functioning centre.

When the ROC telegraph network was introduced in 1968 it was piggy backed on the existing speech network using Speech plus Duplex technology. The actual network connecting the 25 Group Headquarters in the UK had 53 links. Whereas a fully interconnected system would have needed 300 links many of which may never have carried a message.

 

The Teleprinter for the ERA 1 Telegraph Network

A teleprinter of the cold war era was a large Electro-mechanical device resembling an electric typewriter. There was a large public network of machines in the UK, which due to the high cost was almost exclusively for business use. The UK public network was dial up in a similar way to the telephone network but the two networks were not connected. Some large companies had the own independent network which more than likely used Post Office leased private circuits. The Post Office Telegrams division had its own 'TASS' private network up until the 1970's, used for sending public telegrams. This used Creed 47 designated as British Post Office No.11 machines that printed on a thin strip of gummed paper for sticking onto the telegram document.

Before the FAX machine became popular with businesses during the late 1980's, Teleprinters were favoured as an 'instant' communications medium as they produced a hard copy. The data rate, which was considered fast at the time, was 50 baud, with a 5-bit code plus 2.5 start and stop bits. The signalling was by sending 80 Volts Positive and 80 Volts Negative along the two wires. A good typist could type faster than the machine could send the characters, to prevent this happening the keyboard was mechanically locked to prevent a second key being pressed until the previous character had been sent.

Teleprinter No 7

The original Creed 7B here on the right is shown in a configuration for the British Post Office TELEX network. The 7B could be used on point to point links and terminal points on the network but as it had no paper tape facilities. Separate tape perforators and tape readers were required. The large box under the desk but normally located in a more convenient place is the power unit providing the 80 volts DC signalling.

The No.7 designed in 1931 is ingenious consisting of hundreds of moving parts. This was the mechanical equivalent of the UART found in computer modems and decoded the 5-bit code and printed the character on the paper. Only capital letters, numbers and a limited number of special symbols were available.

An improved version of the No.7 the 7E used a different clutch arrangement overcame the problem where the 7B printed one character behind the one being received. In the photograph below this version of the 7E is the 7ERP as it includes a tape perforator. The electric drive motor and speed governor (the black a white round box) which powered both the printing mechanism and keyboard can be seen at the front left.

Teleprinter No 15

The Creed 444 introduced in 1966 and designated the British Post Office No.15 replaced the old noisy No.7 printers for business use. The new machines had two colour printing, a built in paper tape perforator and reader. They were much easier to use as they had an improved keyboard and could store keystrokes. Later on screen based telex machines were introduced, but the No.15 gave good service until the closure of the telex network.

Although the Teleprinter No15 became well established in the public network during the seventies I have little evidence it was adopted for the UKWMO networks by 1980. The reliance on a good mains supply may have made it unsuitable for use with standby generators.

 

Telegraph and Speech over the same Landline

At this time, the rental of landlines was very expensive, so to avoid having separate landline for Speech and Telegraph a very clever system known as Speech plus Duplex Teleprinter, S+D or S+DX was used in the UK Civil Defence network to carry duplex teleprinter signals over the same wires as duplex verbal communication. This system was not exclusive to Civil Defence, but was used in the public network too.

This drawing shows the principle of the arrangement. At each end of the Private Circuit (Landline) a box of electronics combines the inter-switchboard speech line with a bothway link to a teleprinter or torn tape message centre. A more detailed explanation is given in the topic S+DX in the tabs at the top of this page.

In the ROC Group control network, the S+DX could be switched to the radio circuit should the common landline fail. A special jack panel was provided to switch from landline to radio. During a weekend exercise a test of switching to radio was usually undertaken for about an hour.

 

ERA 1 Radio Backup to Landlines

Within both the ROC and RGHQ networks radio systems were provided to act as a standby for the landline network.

The ROC network utilised single channel radio links in the VHF band. The more extensive RGHQ network radio links operated on UHF with both single channel per carrier and multiplexed links. The UKWMO radio links used Home Office Hilltop wireless stations equipped with standby generators already used for Police and Fire Brigade radio schemes. All three groups of users were Home Office departments so it made sense using the same hilltop sites. The radio equipment was supplied and maintained by the Home Office Department of Telecommunications (DTELS)

ROC Radio Links

VHF radio links were provided to supplement the landlines. These provided a duplicate speech circuit between switchboards and additionally the telegraph S+DX could be switched over to use this reserve path. The range of a VHF radio link is limited to 30-40 miles, so a number of tandem links were required to connect the long distances between Groups. At the Group HQ bunker, a windup mast carried a number of VHF 3 or 6 element yagi aerials, pointing at the nearby DTELS hilltop sites. The chain of hilltop sites had 6 element Yagi aerials carrying the links, one aerial was used for both transmitter and receiver. Some Hilltop sites would have more than one link between Group Headquarters passing through them.

Here is a mast with a number of Six element yagi aerials exactly like those used on ROC links. The aerials are either mounted with their elements horizontal or vertical. Aerials at each end of the link will have the same element polarisation. An aerial of the opposite polarisation only receives a weak signal. This can be exploited to allow the same radio frequency to be used in the order of fifty miles away if the polarisation is different.

In this first era 1960-s - 1970's the bands were 147.000-147.300MHz paired with 155.000-155.300MHz which were a sub band of the larger 146-148MHz and 154-156MHz frequency assignment for Emergency Service use. An exclusive Civil Defence band 168.325-168.800MHz paired with 174.025-174.500MHz was used for the ROC in accordance with notes N27 N29 in UK Table of Radio Frequency Allocations 1985, ISBN 0-11-513819-6

The enlarged map shows all the individual radio links emanating from Wrexham, Shrewsbury, Coventry, Bedford, Lincoln and Norwich. Other group controls do not show their full compliment of links as I only have the full details for a few sites. Oxford for example, would have had links to Bristol, Yeovil, Winchester and Horsham additionally to the three shown here from Bedford, Coventry and Shrewsbury.

It has been suggested that not all the inter group radio links actually worked and some worked but where not formally commissioned. All the links were switched off as part of the W.A.R.C. project which changed the emergency service radio frequencies during the mid to late 1980's. The ROC link frequencies were allocated to the emergency services when they migrated from 100 MHz, it was the intension to use the RN1 and RN2 networks described on the next page for the links.

RGHQ Radio Links

In this first era the bands used were 452.000-452.300MHz paired with 466.000-466.300MHz and some additional channels in the larger 451-453MHz and 465-467MHz Emergency Services band which was mainly used for Police personal radios. There were two other bands 455.850-456.000MHz and 468.875-470.000MHz exclusively used for RGHQ links.

UHF link yagi aerials were of this design used on this link between the council control centre and the RGHQ. The shorter UHF wavelength means 12 elements can be used instead of 6 used in the VHF spectrum.

Compared with a ROC HQ, there were a large number of circuits radiating out from a typical RGHQ, which dictated a different linking arrangement. If they operated a single channel per carrier as did the ROC there would be problems due to the large number of individual transmitters, receivers and aerials required at the RGHQ as well as the hilltop sites. A technique known as multiplexing allows a single radio channel to carry seven circuits. One circuit is carried at normal speech frequencies and six are translated to higher frequencies, the resulting combined output is used to modulate the radio transmitter. The radio receiver output is fed into a demultiplexer to separate the individual speech circuits. A pair of multiplexer / demultiplexer equipment is needed at each end of the radio system.

A more detailed description of the speech multiplex process may be found on the further reading link at the foot of this page.