R.O.C. Observer Post Communications - ERA 2
We examine the changes introduced in the 1980's to improve the reliability of communications with Observer Posts.
Improved ROC Post Communications
Starting in 1981, the landlines to Group Headquarters were converted from switched Emergency Circuits to permanently connected Private Circuits (Private Wires 'PW'). The previous arrangement of switching the lines meant this could only happen for main exercises. Therefore the TeleTalk couldn't be used on a normal drill night. The change to permanent circuits made it possible to communicate with the other posts in the cluster and Group HQ at any time.
The new Private Circuit to Group HQ operated over four wires, one pair conveying the both speech to the post TeleTalk and the carrier plus power for the warning receiver. The other pair conveyed the TeleTalk speech from the post and supplied the power to the TeleTalk unit. This led to an improved quality of communications around the cluster and back to Group. The very vulnerable overhead lines were replaced with an underground cable. At some sites the poles were not actually removed by BT and in some cases are still present now.
During the mid Eighties, the old valve VHF transceivers in master posts were replaced with modern sets, still working on VHF, but using low band for improved coverage in comparison to highband.
Landline link to Group
Teletalk Unit AD8010
The original grey TeleTalk was replaced with the more modern AD8010. This derived its electrical power from the public telephone exchange 50 volt battery via the private circuit thus removing the need for a stock of batteries at the post.
Landlines within a Cluster
This new design of TeleTalk still retained the simple controls of the earlier model. The 'CALL' button calls the attention of Group. The device is normally in receive mode and monitors any conversations taking place on the Private Circuit.
The 'TRANSMIT' button must be depressed to switch to talk mode. This is very much like a operating a radio transceiver. The loudspeaker and microphone are in the hinged lid that is normally kept closed to press the 'ON' button down to switch it off. When in use, the lid could be angled to suit the user, who speaks about 9-12 inches away from the microphone.
Loud Speaker Unit WB1401
As part of the modernisation of the UKWMO communications system during the 1980’s the older early warning receiver was replaced with line powered units removing the reliance on dry batteries. The power for the warning receiver and the voice carrier signal was sent over the pair of wires to transmit speech to the TeleTalk.
A Receiver Carrier WB1401 was used by the ROC as their new early warning receiver was as it was designed to respond to a 'SELECT' call from the Carrier Control Point. This meant the Police could issue messages during exercises without disturbing non ROC Warning Point receiver owners. The operation of early warning system code named HANDEL is fully described in other pages on this site accessed from the top navigation tabs.
In damp environments, such as ROC Posts, the early warning receiver had a ruggedised and damp proof speaker, the "Loud Speaker Unit WB1401". However ROC Group Headquarters would employ the same receiver but with a plastic cased speaker more suitable for an office.
Master Post Wireless RN4
ROC Post Radio in cabinet
As a backup for the landlines, from 1972 onwards the master post of the cluster was equipped with a VHF radio allowing it to contact the group headquarters independently of the TeleTalk. If only part of the private circuit was damaged by war action, the master post would relay the readings from any other post still remaining in contact, to the post display plotter.
Master post radios were modernised from single channel valve set to three channel transistorised equipment. The Burndept BE525 radio was housed in a locked cabinet shown here. As well as its own Group's channel the set could be switched to two other adjacent Groups which would be helpful if their own Group was destroyed by enemy action. Using only a single frequency simplex channel meant that all master posts could make contact with others within range. This opened up the prospect of relaying messages to Group should radio conditions mean that direct contact was no’t possible. This second generation wireless scheme was denoted as Radio Network No4. (RN4)
ROC Post Radio Channels
This table shows the radio frequency used by each group. Posts belonging to that group had this frequency as Channel 1 in their sets. Radio Channels 2 and 3 in Post radios were allocated to frequencies of adjacent groups. All radios used FM modulation with Code Tone Control Squelch System (CTCSS). Tone 1 is used on all radios when working on the Primary Scheme with tones 3 to 5 for the secondary scheme.
A block of twelve frequencies were shared amongst twenty five UKWMO Groups. These twelve channels were in part of the Home Office allocation of 80.000-81.500 MHz also used by the UK Fire and Rescue authorities for mobile to base communications, before they switched to Airwave. The limited range of VHF radio signals allowed more than one Group to use a particular radio frequency without causing interference.
ROC Post Radio Scheme
The RN4 Primary scheme which was installed as Phase 1 of the communications upgrade had Group and Posts all transmitting and receiving on the same frequency and CTCSS Tone 1. While this worked for master posts in close proximity to Group HQ, the more distant posts and those in difficult terrain could not contact headquarters directly.
The RN4 secondary scheme which was only partially rolled out before stand-down used hilltop repeaters in areas where posts could not make direct contact with Group. Up to three hilltop repeaters could be linked back to group using VHF highband radio links. Posts out of direct contact range of their group headquarters would select a CTCSS tone number for their nearest hilltop. All the hilltops used the same group frequency but with a different CTCSS tone for discrimination.
In the Group control, the radio scheme was connected into the internal telephone system. The Post Supervisor had a small control unit associated with their TX14 telephone. This had a Press To Talk (PTT) button to control the radio. If necessary the post display plotter could join in the radio messages by setting up a conference call. However the post supervisor would have to operate the PTT button.
ROC Post Radio Channels
|Ayr||AYR||???|| || |
|Dundee||DUN||80.2750|| || |
|Edinburgh||EDI||???|| || |
|Inverness||INV||80.2875|| || |
In England, Wales and Northern Ireland, the Home Office Directorate of Telecommunications was responsible for the radio scheme. In Scotland this was the function of the Scottish Office and little information appears to be available nowadays for the five Groups under their control. ROC Documentation from England appears to suggest there were no cross border communications and omit the Scottish Groups from the interconnection diagram. The channels marked on the only Scottish radio I have seen suggests that inter-group communication was only possible within Scotland.
The table on the left was obtained from the designation plate on one post radio. I would greatly appreciate any feedback to complete the missing parts of the table. Feedback via my Home Page please.
Monitoring Post Pump Up Mast and Aerial
Click image to view all of mast
The aerial chosen for the monitoring post radio is a dipole encased in a green glass reinforced resin tube. This is mounted on a guyed pump up mast. The inflation of the mast is performed from the safety of the monitoring room via a pipe running from the aerial connection box.
This photograph of a print taken by Martin Cooke, Chief Observer at Stoke Golding, shows the mast and antenna during an exercise. The FSM dome and GZI can be clearly distinguished too.