Overview

MOULD first came to my notice in January 1987 when an article in the RSGB Radcom warned radio amateurs that links between MOULD hilltops were using the 70 cm band that we shared on a secondary basis. The article explained that MOULD would provide communications between Regular Army, TA Battalions and the Army District and Regional Headquarters. Phase 1 cost £7m to install and used 18-channel Pye Pegasus radio’s operating at 66-88MHz. A network of hilltop sites were linked together to give area coverage. These bearer links used 140-150MHz and 420-450MHz in a formation giving a maximum of 7 radio hops between users.

Having been alerted to the presence of the system, I was able to find the frequencies being used locally for the area coverage and the inter site links. I never had the inclination to investigate military communications and back then did not appreciate MOULD's connection with home defence. Only after the scheme closed down has this become apparent, in June 2009 I obtained a copy of a technical article published in the mid-80's that has filled in the gaps in my knowledge and is the basis for this revised topic page.

MOULD closed during the mid-2000's and the users have been transferred to AirWave the common system for UK Emergency Services communications used by the Police and Fire authorities. The MOULD equipment was being recovered from hilltop sites during 2008.

 

The Radio Network

Phase One of the UK Army MOULD radio system was introduced during the early 1980’s in England, Scotland and Wales but not Northern Ireland as communications were already in place. It was designed to give area coverage in each of the home defence regions that align with the civilian Regional Government Headquarters (RGHQ) boundaries. In the mid-80's Phase Two provided additional schemes giving area coverage in each county.

In order to give area coverage a number of hilltop sites working in the VHF low band were connected together with radio links operating in VHF high band or UHF. The schemes were designed so there were no more than five links in between any two sites. In this drawing of the Phase One network in Home Defence Region 7, there are two sub networks. In the sub Region 7.1 under control of the RGHQ at Chilmark there are nine hilltop stations and nine in sub Region 7.2 controlled by Bolt Head RGHQ. Three of the sites are common to both networks. Countrywide, Phase One employed 120 hilltop sites. This increased to 150 when Phase Two was implemented.

Most of the hilltop sites chosen were owned by the Home Office for use by the emergency services. Some MOD and Civil Aviation sites were used too. I do not have a list of the actual sites but inspecting this map shows a strong correlation between MOULD and Home Office mast locations. The hilltop radio equipment was maintained by the No2 Signals Brigade.

In Phase 1, the MOULD mobile and fixed sets were 18 Channel crystal controlled Pye M252 Pegasus transceivers outputting 5 to 15 Watts in the 79MHz band and receiving on 74MHz. In Phase 2, Pye FM914 25 Watt synthesized 250 channel transceivers were used.

The hilltop radio equipment was all mains operated. The Area channel equipment was a Pye 400 Series 60 Watt transmitter with a separate receiver operating in the VHF low band 74-80MHz. VHF links operated with a Pye T404 25 Watt transmitter and separate R404 receiver. UHF links used a Pye T414, 5 Watt transmitter and separate R414 receiver.

 

Network Design

The design of the MOULD network is very different from the wide area schemes used by the emergency services. Emergency services have a number of hilltop locations all transmitting and receiving on the same frequency and linked back to a single control point. A full description is given in the 'Emergency Services Era 1' topic. In contrast each of the MOULD hilltop sites use different pairs of transmit (TX) and receive (RX) frequencies. The MOULD network did not have a central control point so adjacent sites were linked together in an open network. A limit of five serial links was imposed to ensure reliable communications.

Referring to the diagram on the right of this text, each mobile would select the channel used at the nearest hilltop. For mobiles M1 and M2 this would be Channel 5. If M1 called M2, its signal would be received at the hilltop and be rebroadcast so M2 could hear it. As well as simply rebroadcasting the signal, it would be sent on the link to the next hilltop and broadcast on Channel 4, this site would relay the signal on the link to the next site. Here it would be broadcast on Channel 2, so mobile M4 could hear the signal. This site is linked to two others, where it would be broadcast on Channels 1 and 3. Mobile M3 would also hear the signal. If M3 called M2 too, it would transmit on Channel 1, its message would be similarly broadcast by all sites on the network, so all four mobiles including M2 would hear the message.

On any particular network, each hilltop was permitted to have a maximum of five links to other sites. One of the sites shown on the Region 7 maps has five links in sub-network 7.1. The are also two links forming part of network 7.2 but this has a separate set of equipment. Not shown in the drawing, that site also had a third set of equipment in Phase 2, on the Somerset County network.

The hilltop radio equipment was controlled by a 'Control Switching and Signalling Unit' (CSSU). The CSSU routed the signal from the receivers to the appropriate transmitter. The logic diagram shows that any signal received on the low band area channel was rebroadcast by the area channel transmitter and all the link transmitters. A signal received on a particular link would be broadcast by the area channel transmitter and all the other links except the originating link.

The Emergency Services radio schemes had all their transmitter and receivers were duplicated. This was not the norm for MOULD except at the more remote hilltop sites where link radio and rebroadcasters were duplicated as access could be difficult in adverse weather conditions. To guard against the loss of a hilltop site, mobile units were available that could be driven to the site to replace it while repairs were undertaken. Where two or more networks shared the same hilltop, the CSSU could link together to enable the networks to be joined together for fault finding or operational reasons.

 

I don’t know the exact upper and lower limits of the bands used for MOULD but the table below gives an indication of the sort of frequencies used. All appear to be in bands shared with both fixed and mobile military services.

• Mobile Transmit 79-80.000MHz
• Base Transmit 74.000-74.800MHz later extended 75.700-76.700MHz
• VHF links 141.900-143.000MHz and 149.000-149.900MHz
• UHF links 421-422MHz, 429MHz, 433.0-433.5MHz

For an example, in my notes during an exercise in October 1988, 74.050MHz 74.125MHz 74.200MHz 74.525MHz Base station transmit frequencies were all carrying the same traffic. If this were the Region 92 cluster of hilltops, four would seem reasonable for this relatively small geographical area. Also noted on 29-11-1986, 800Hz tone and howling heard on these two Base TX 74.3375MHz 74.5375MHz and three Links 142.5875MHz 149.0625MHz 149.8875MHz

 

FEEDBACK - An Example from Region 8

In Wales there were two Principal Networks, Region 81 in the North and Region 82 in the South, corresponding with Brackla RGHQ 82. The were County Networks too, in Region 81, these were Clwyd and Gwynedd; in Region 82, Dyfed, Mid, South and West Glamorgan, Gwent and Powys.

The County Networks consisted of one or more hilltop sites, Mid Glamorgan had one rebroadcaster whereas Powys had a network of four. If desired, County Networks could be coupled in with the Principal Network, Abergavenny was the coupling point for Powys and Gwent into Principal for Region 82, Dyfed could be coupled at Mynydd Sylen. Network control including coupling was performed remotely by the use of SELCALL signals. The Hilltop site at Old Pale is located in Region 10, and also has 3 rebroadcasters on those networks. Similarly Brown Clee has two rebroadcasters on its Region 92 Networks.

The older Pye Pegasus radios only had 18 channels, so each Region had its own version of the radio with the appropriate frequencies for the hilltops in its channels. The Pye 914 sets had sufficient channels to cover the country. Some of the rebroadcasters on this map use the same frequencies but they are sufficiently well separated to avoid interference.

 

Civilian Use of MOULD

In the nineties a program of fitting MOULD aerials to civilian buildings was undertaken. Aerials were fitted to main telephone exchanges and wired to the protected accommodation but no radio equipment was connected. Council emergency control centres also had aerials fitted like the one shown here. UKWMO Group Headquarters and RGHQ's had MOULD fitted.

In Cambridgeshire they tried and tested an interlink between the County Net radio scheme and MOULD allowing direct communication between the two systems. This was demonstrated at a Civil Protection conference at Scarborough in June 1995.

As similar aerials have been spotted on other buildings as well as Police and Fire stations these may have be wired for MOULD too. I can only speculate that this would allow military liaison at those places in a civil emergency.