ROC Communications
Post to Group Communications
Teletalk Landline
Each cluster of posts were connected by a landline to the Group HQ plotters. The Teletalk arrangement has been described in an earlier topic describing the ROC Post.
Radio
The master post within each cluster was equipped with a VHF radio allowing it to communicate back to Group, independently of the TeleTalk landline. If the landline became disconnected from Group, the master post would gather readings from the other posts in the cluster (assuming this part was still working) and relay them to Group.
Before the change of equipment and frequency to 80Mhz in the mid-1980's the post radios used dual frequency simplex. This meant the posts would listen on one frequency and transmit on another. Due to the frequency split, posts could not speak to one another. Whilst it meant Group was always in control of the radio waves, there would be no post to post intercommunication if Group was destroyed. During the time of my involvement, Bedford Group usually operated their radio scheme with talkthrough (they called it 'Bounce Back') turned on, allowing posts to hear both sides of the conversation.
The frequencies used for the Post to Group HQ radio schemes were in the same bands used for Inter-Group circuits described below.
Due to the limited range of VHF radios, Hilltop radio sites relayed the signals via VHF radio links back to the Group. Group HQ's were fitted with a wind up mast, carrying a number of VHF yagi aerials pointing at the hilltop sites. These also carried the inter-Group radio circuits, described further on.
Inter-Group Speech and Teleprinter Circuits
Group Communications
This section refers to the period from setting up the UKWMO, to the modernisation of communications during the early 1980's.
Each Group HQ had a Communications Centre for transferring messages to and from other Group HQ's. Each Group HQ bunker had a manual telephone switchboard with lines into the public telephone network and many extensions. In addition, there were two dedicated connections to each adjacent Group HQ. One was a landline and the other a radio link. These allowed officers at one Group to speak to their counterparts in an adjacent Group. Group also had a landline and radio link to the Sub-Regional Government HQ (SRHQ) A Warning Broadcast Receiver was provided too. As explained on another topic page, the Group HQ had lines to the Carrier Control Points (CCP) located in police stations so they could issue fallout warnings to the public.
Bomb detonation reports and fallout readings, would be sent by teleprinter to adjacent Groups. This transfer allowed each Group to build its own charts predicting the onset of fallout. For example, with the prevailing West wind in the UK, a bomb in the Coventry patch could produce fallout in the Bedford Warning Districts.
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This diagram shows the links in Red between Bedford and the other Group HQ's. All Groups were similarly connected to their neighbours. To guard against link breakdown, Group HQ's could act as message relay centres. The teleprinters produced a punched tape, which could be resent via another teleprinter link. So for example, if Bedford lost its connection to the Sector HQ at Lincoln, the message could be relayed via Norwich. The use of punched paper tape, meant the same message could easily be sent to more than one destination. These were known as torn-tape relay centres, similar centres existed at the SRHQ. The message centre is described on the next page.
Land Line Links
Group HQ's were provided with landlines connecting them to adjacent Group's and their own Sector HQ. The landline carried normal two-way speech and by a clever arrangement known as S+DX simultaneously carried teleprinter messages too. This was accomplished by converting the 80-volt teleprinter signals to audio tones, then filtering them into part of the speech band. A more detailed description of S+DX may be found on the link at the bottom of this page.
VHF Radio Links
The ROC radio systems were provided and maintained by the Home Office Department of Telecommunications. (DTELS) The frequencies used being part of the spectrum allocated to the Home Office. The hilltop sites were Home Office sites used for Police and Fire Communications as DTELS provided these systems too.
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VHF radio links were provided to supplement the landlines. These provided a duplicate speech circuit between switchboards, in addition the teleprinter 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 wind up mast carried a number of VHF 3 or 6 element yagi aerials, pointing at the nearby hilltop sites. The chain of hilltop sites had 6 element yagis carrying the links, one aerial was used for both transmitter and receiver. Some Hilltop sites would have more than one link between Group HQs passing through them.
The bands used in the 1970's were 147.000-147.300MHz paired with 155.000-155.300MHz and 168.325-168.800MHz paired with 174.025-174.500MHz According to notes N27 N29 in UK Table of Radio Frequency Allocations 1985, ISBN 0-11-513819-6, but since 1987 have been reallocated for other uses. The radio equipment was supplied and maintained by the Home Office Department of Telecommunications "DTELs". The ROC frequency bands were part of DTELS larger frequency assignment for Emergency Service use.
UHF Radio Links
The Group HQ would be linked to its local Sub-Regional Government Headquarters (SRHQ) Bunker, by landline and UHF radio link. The County Council Emergency Control Rooms were also connected to the RGHQ by both landline and radio too. The UHF links were to the same hilltop sites as the Inter-Group links. The bands used were 452.000 - 452.275MHz paired with 466.000 - 466.275MHz. The UHF yagi for this link was on the same wind up mast as the inter group link aerials.
1980's UKWMO Communications Modernisation
Public Warning Broadcast System
The warning broadcast system WB400/WB600 was replaced during the early 1980's by the WB1400, as described in earlier Pages on the site. The WB1400 ceased to be operational in the early 1990's when the Cold War came to an end and civil defence was scaled down.
ROC Post Teletalk Unit
At the same time as the Warning broadcast receivers were changed, the ROC Post Teletalk was updated too. This new unit was line powered from the telephone exchange and didn't require batteries like its predecessor.
Radio Communication Frequency Changes
During the 1960's and 70's police and fire radio base stations transmitted in the frequency band 97 - 102 MHz. These utilities were forced to move to make way for FM broadcast stations. During 1986/87 many changes were made to the frequencies used by the Home Office known as the WARC program. The original 147 and 155MHz ROC frequencies were reused for police and fire services.
ROC Post Radios
The original radios were single channel VHF high band, transmitting and received on different frequencies. This allowed them to communicate with their own Group HQ whilst preventing them speaking to other posts.
The replacement radios operated in VHF low band used by firebrigade mobiles 80.000-81.500MHz, a total of twelve frequencies were allocated for ROC use. They used the same frequency for both transmit and receive allowing intercommunication between posts too. The new post radios had three channels enabling them too operate on two adjacent Group HQ frequencies should their own Group HQ be out of action. If you wish to read more about the frequency allocations, follow the link at the bottom of this page.
Inter Group HQ Radio Links
VHF links were retained from Group HQ's to the first hilltop site, but between sites the links were carried on frequencies between 1500 - 2000MHz. The links were multiplexed onto carriers in these bands, which meant a single carrier could carry a number of separate speech channels.
Message Centres
The torn tape teleprinter message centres at ROC Group HQ and Sub-Regional Government HQ as described in the next topic were replaced by an automatic switched network. This system extended down to County Council controls. ROC Posts were not included in this scheme.
Voice Communications
The Emergency Communications Network (ECN) was introduced. An extensive automatically switched network replaced the previously fragmented network which often relied on the public telephone network to connect between the fragments. For the first time Police, Fire, Councils, ROC and Sub-Regional Government HQ's were all connected to the same emergency network, working independently of the public network.