My Search for the ROC Inter-group Radio Links

This topic describes my search for the path taken by Royal Observer Corps (ROC) Group HQ radio links. This started in 1979 and ended when I moved to Birmingham in 1981. How these radio links were used by the ROC is described elsewhere on this site.

Background

Typical HO Mast

Typical Home Office Radio Mast

The situation regarding radio masts at the end of the 1970's was very different from today. There were very few lattice towers to be seen in the countryside, unlike now where mobile phone masts may be found every few kilometres. The cellular phone did not make its appearance until the late 1980's, ten years after this episode in my life. Those lattice towers that did exist were usually marked on maps as significant features. The use of the masts could be relatively easily determined by visual examination. Home Office masts could be easily identified by their VHF 6 element Yagi aerials used to link the hilltop sites to the police or fire controls. No other services were permitted to use VHF radio links.

With the help of the local library I had gained quite a bit of information about how the police and fire radio schemes worked. The Home Office Directorate of Telecommunications published quite a lot of detail including the frequency bands they used. The band from 97 to 103 Megahertz was used for the Emergency Services much to the consternation of our European neighbours, who used it for broadcasting. The general public used to listen into the police and fire transmissions using their Stereo's (VHF FM radios) but reception of the AM signals were poor. Only the control room side of the conversation could be heard, so the juicier bits, the mobile side of the conversation was replaced by a pip tone. Weaker distant signals from other counties would be blotted out by strong local signals.

Towards the end of the seventies reasonably cheap 'Wideband' commercial radios intended for the American market became available in ordinary shops that covered the Air Band 108-138MHz and Public Service 144-174MHz as well as the usual FM broadcast 88-108MHz band. Scanning receivers were not available to the general public at that time. The one I purchased would be 2,000 in today's money [2013].

The Emergency services vacated the broadcast band during the mid 1980's and moved to another frequency band. By the time this happened scanning receivers had become available but their high price limited availability. When analogue mobile phones appeared in the early 1990's the sales of scanning receivers boomed as people bought them to eavesdrop on peoples phone calls. The owners started to listen to emergency service transmissions too to such an extent that nothing was now private.

During the mid-2000's the Police moved to a totally secure radio system and the Fire and Ambulance authorities followed by the end of the decade. The Public Safety Radio Communications known as 'Airwave' in the UK, provides a communication network on European wide standard digital encrypted voice and data using a common set of frequencies, putting an end to eavesdroppers.

The Initial Discovery

A number of factors came together around 1979. Firstly a friend, who used a 'Wideband' radio to listen to the fire brigade link frequencies, reported his reception blocked by a very strong signal containing white noise. Using my amateur radio receiver to tune above the 2 metre band. The white noise turned out to be on 147.000 MHz, which was in the Home Office band. It did not take much effort to trace the signal to the nearby HO hilltop site at Old Gorse. (Not a secret - The local newspaper carried an article when a new mast was installed for the 'Police' at Old Poor's Gorse) This signal persisted for a few weeks then disappeared, I assume the fault was cleared. The final thing was changing jobs and as a result had to visit ROC sites. Details of their exercise were available which indicated when radio tests were being performed.

On the first occasion that I was aware a ROC exercise was taking place, I decided to try to find their frequencies. A hunch made me listen on the frequency where we had heard the white noise. Much to my surprise, there was Bedford talking to its posts. Further tuning between 147 and 147.3MHz revealed other frequencies in use. Unlike the On-Off transmissions to the posts, these were continuously on. I had stumbled on some of the frequencies used for the Inter Group links although none were coming from Old Gorse, but from the North and South of my location. At this time is was only able to listen between 146 and 148MHz with my amateur receiver designed for the American market and it required the purchase of a scanning receiver for things to progress.

Hunting down the Masts

The next thing was to pay Old Gorse a visit to see what was going on there. High up the mast were yagi aerials pointing in the expected directions for the police and fire services. However lower down the mast were two VHF yagi aerials pointing north-westerly and three pointing south-easterly, these had to be for the ROC. Next came a visit to Bedford ROC HQ, in Bromham Road, Biddenham. This had a wind up tower, currently in the down position as no exercise was in progress, containing loads of VHF 3 element yagi aerials. Two pointing North East, Four South and Three East-Southeast. Additionally a 6 element yagi pointed North-Westerly in the direction of Old Gorse. However there were three aerials at Old Gorse but only one here at the ROC.

On the way home, I spotted a Home Office mast at Twinwoods Farm, Oakley, just North of Bedford. On diverting to pay it a visit there were the expected Police yagi's high up pointing into Bedford. Again lower down the mast, two 3 element yagis pointed toward ROC Bedford matching the two 3 element yagis there, pointing north-easterly towards us. There were two 6 element yagis pointing north-westerly towards Old Gorse. This completed the match in a northerly direction, but opened up questions why two radio links came via Twinwoods to Old Gorse, and one went directly (answered later) to Old Gorse.

It seems so sad to say it now, but I planned my 1979-80-81 holidays so I could visit as many ROC locations in the East of England as possible and trace out the links by looking out for masts on the way. As I said previously, many were marked on the map, so this was not too difficult.

Hunting the Frequencies

Things moved on when I purchased a scanning receiver. Every Friday morning the ROC tested their communications links. The radio test was done about 10am. So it was a case of being near a mast at the right time. I was able to have a Friday off from work every fortnight, which facilitated the search. Luckily each link was tested separately which enabled both the strong local transmitter to be heard and the link back from the next mast. Travelling meant only the links in the vicinity of my home had their frequencies measured.

Old Poor's Gorse [1980]

Old Poor's Gorse 1980

The frequencies were arranged in two pairs of blocks. A duplex link requires speech to be transmitted simultaneously in both directions necessitating two transmitter chains. A link between hilltop sites would normally use matching channels in each direction. For example, on the Coventry - Bedford circuit, its link between Old Gorse and Skeffington used 147.150 in the Coventry to Bedford direction and 155.150 in the Bedford to Coventry direction.

Measuring the frequencies used at masts answered the puzzle about why two of the three northbound aerials Bedford Group HQ pointed at Twinwoods, those were the two inter-group links. Whilst the third aerial pointed directly at Old Gorse as it was added some years later for the link to the repeater on the Group to Post Radio scheme

I was able to determine all the VHF frequencies used at Old Gorse, my closest mast. These are shown on the right hand diagram and includes two Northamptonshire Police M2NG channels (BLUE), Northamptonshire Fire M2NO (RED), UKWMO Group HQ links (BLACK) and ROC Post (TEAL). Its in an awful example of frequency planning as there are transmitters and receivers operating in the same band.

Finding the Regional Government Headquarters (RGHQ) or not

Bawburgh Polaroid [7-May-1981]

Bawburgh RGHQ Mast taken in 1981

Click here to see what a decent camera would have captured.

My friend visited Norfolk fire brigade headquarters in Hethersett and remarked he could see a Home Office style mast about two miles away, but the aerials on the fire control pointed elsewhere. I planned my 1981 holiday to take in Norwich and Lincoln, as they were both ROC Group HQ locations. I investigated the mast my friend had identified and wandered into the woods beside the mast and spotted a bungalow with blacked out windows and various air vents nearby. I had read in the daily papers about Regional Government bunkers disguised as bungalows. Putting two and two together I realised I had struck gold and found a RGHQ near the village of Bawburgh on the outskirts of Norwich. I used a 2" square polaroid to take two pictures of the communications mast, neither are very good, but on this enlargement, the aerials are just visible. Click the polaroid to see a photo taken with a decent camera and slide film.

Links to RGHQ 4.2 [1981]

Links to RGHQ 4.2 1981

The mast contained seven VHF yagi aerials that appeared to be ROC links. There were thirteen UHF yagis, my scanner revealed seven UHF carriers emanating from the site. One of these on 466.025 matched 452.025 being transmitted at the Norwich ROC group HQ. The UKWMO booklet showed a link from Group HQ's to RGHQ's, so this confirmed I had indeed found gold. Up until now I had not paid any attention to the UHF yagi aerials although I had seen them at all group headquarters. There were numerous UHF yagis on Home Office hilltop sites pointing in all sorts of directions but I had no explanation of their purpose until now. A strong signal on 452.125 in the vicinity of Norwich City Hall had a matching link at the Bawburgh end on 466.125, although they did not appear in the UKWMO booklet, Council headquarters also had links to their RGHQ.

Later in the holiday at a hilltop site near Fulletby in Lincolnshire, I started paying attention to the UHF yagis, which pointed in various directions, but strangely four were pointing eastwards, not in the direction of any habitation centres. Eighteen years later, when I first stumbled on the SUBBRIT web site, I discovered that a RGHQ was located 9 miles away at Skendleby which fell almost directly on the line I had drawn on my map in 1981. If only I had driven down the line on that day. On the same holiday I visited masts at Caistor, Kirkby Underwood and Carlton Scroop before returning home.

On a Friday off work, I visited Bedford ROC to measure the links during the test and then drove to the Reed hilltop mast (named Thurfield by the H.O.), there were twelve UHF yagis, a carrier on 451.150 matched a 465.150 signal I traced to Sovereign House, Hertford. However being totally unaware of the locations of the RGHQ's I had just assumed this was like the other UHF links from a typical County Council. At Bedford, the Council HQ (466.175) and Bedford ROC (466.125) had links connected to Twinwoods (452.125 & 452.175) then relayed out (452.150 & 452.225) towards Reed (466.150 & 466.225). There were two other links at Reed, 466.025 went on to the Streatley mast where it was relayed on to an unknown destination, possibly the 'Bedfordshire Standby' council bunker wherever that was. One remaining frequency at Reed, 466.125 was never traced. There were many more UHF aerials pointing in different directions than can accounted by the measured frequencies.

Mistakenly had assumed that all these links around Bedfordshire and Hertfordshire eventually led back to Bawburgh and not that Sovereign House was itself a RGHQ. So in hindsight, this was the second RGHQ to slip through my fingers in a matter of months. In early September 1981, I heard that I had passed my promotion board and would be given a job in Birmingham. The summer of discovery came to an end when I moved home in October. This stopped any further investigations otherwise more might have been revealed. In July 1982 after my house move, I went to the company's training school in Staffordshire and noted a number of very strong UHF signals but didn't pursue them which is a pity as they were coming from RGHQ 9.1 only a mile away at Swynnerton a third RGHQ had slipped through my grasp. But all would be revealed in eighteen years time, but sadly that was eight years after stand down.

Conclusion

Due to the ease in which Home Office hilltop sites could be recognised and that the ROC links were always lower down the structure than the police and fire links, the job of tracing parts of the ROC network was made easier. It is interesting to note the ROC was the poor relation to the other services, it used one aerial for both transmit and receive whereas the police and fire had two separate aerials.

As a total outsider I was pleased with what I had discovered, I am sure people who worked for the Home Office Directorate of Telecommunications (DTEL's) would laugh at my pathetic attempts. I would love to know if the whole UKWMO network was documented and perhaps before my death the archives may be released to reveal the true path of these links and confirm if the frequencies were indeed correct. Duncan Campbell's War Plan UK would have been a great help in locating the RGHQ's, but I was unaware of its publication. In the mid-1980's the network described here was replaced and many of the radio frequencies used for other services.

The Parts of the Network I had Discovered by 1982

Midland Sector Actual Links [1982]

Links between UKWMO Groups

My change of job in October 1981 and a house moved forced an end further research. This diagram and the enlarged view showing all the detail is based on the final hand drawn map I drew in 1982. I have added some extra notes now that I'm aware of hilltop sites that I hadn't discovered back then.

These additional hilltop sites have been located via the internet, by searching Google, by browsing photographs on www.geograph.org.uk and articles on www.dtels.org Without the benefit of the internet back in 1981 it was a case of drawing a line on a map and hoping you could spot the mast on a subsequent visit. Of course as the net spread wider from my home location this became difficult and costly.

Please click on the link underneath the thumbnail to see all the detail of the sites and link frequencies. Some frequencies were not found but the lines are still included. Arrows indicate links that were not pursued beyond that point. I'm just so sorry I didn't put more effort in to finding the links way back then. In April 2013, photographs of the Bawburgh mast taken in the seventies were released by SubBrit, it is now clear that some of the aerial headings I had recorded were wrong, the map in the next topic has these errors corrected.

Filling in the gaps : Thanks to Feedback to the website

The diagram below, when enlarged with the zoom, shows details of the links, their frequencies and mast locations in Central England and North Wales. Hopefully now that 30 years has passed and the official secrets act bar lefted on the UKWMO radio scheme of the seventies, people will come forward with details of other ROC Group areas.

Updated UKWMO VHF Links

Links between UKWMO Groups

As result of reading this page in 2004, Martin sent me a copy of a drawing he found blowing around a car park near a Home Office hilltop site that was being cleared 10 years earlier. This was a hand drawn sketch of a diagram CB429 showing the UKWMO VHF radio links. The sketch is of particular interest as it dates from 1978, the same era as my research. The drawing only shows the links passing through North Wales or on routes from Wrexham Group Headquarters.

Mike Hawkins has kindly provided copies of a former DTEL's engineers notes showing the links from Shrewbury and Coventry groups. I have redrawn all the original diagrams <link> to improve readability and added the OS Grid references of the sites. Other group controls do not show their full complement of links as I only have the full details for the few sites shown here. Oxford for example, would have had links to Bristol, Yeovil, Winchester and Horsham additionally to the three shown here from Bedford, Coventry and Shrewsbury.

If you have any personal notes relating to the VHF Home Defence links, enabling more paths to be plotted then please get in touch via my homepage link at the top right of this page.

The radio link from Belfast to Preston involved a 118 mile long path across the Irish Sea between Slieve Croob ( IJ316454 ) and Cefn Du ( SH835733 ). Further enquiries have revealed it operated using standard VHF link equipment and a 70 Watt amplifier feeding an 8 over 8 Yagi array. The radio backup to the landline circuit from Belfast to Carlisle had a much shorter link to the mainland (where?) from Cairngaver ( IJ454765 ). The Belfast Ayr landline link did not have a radio backup.

The network shown was switched off during the mid-eighties when many of the link frequencies were allocated for Police VHF communications as part of the WARC project. It was replaced a new system using multiplexed links on frequencies in the 1500MHz band.