MOULD Home Defence Radio

This topic is a simplified description of the defunct MOULD radio system. The original phase provided one system per home defence sub-region and employed 120 hilltop sites. A later contract extended this with the addition of County networks bringing the number of separate networks to ninety and increased the hilltop sites to 150. Based on an article in 'The Wire' circa 1986, by A F Carter with the addition of my own observations.


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 with the Ministry of Defence (MOD). 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 radioís 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. Further information has been forthcoming in 2010 and 2011 allowing more specific details to be added.

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, Fire and Ambulance 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 1976-77 in England, Scotland and Wales but not Northern Ireland as a communications system was 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.

Phase 1 MOULD Network, Region 7

MOULD Network in Region 7

In order to give area coverage a number of hilltop sites with rebroadcasters working in the VHF low band were connected together with radio links operating in VHF high band or UHF. 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 sites Middleton Court, Cranmore Tower and Newton Barrow are common to both networks and have rebroadcasters on both networks. The schemes were carefully designed so there were no more than five links in between any two sites. In Sub Net 7.2 for example the extremities at Four Lanes and Newton Barrow are only five links apart, so are Collaton Cross and Newton Barrow.

Countrywide, Phase One employed 120 hilltop sites. This increased to 150 when Phase Two was implemented. Most of the English and Welsh hilltop sites chosen for MOULD were owned by the Home Office and used by the emergency services and UKWMO. Some MOD, Civil Aviation and Broadcasting sites were used too. All 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.

The hilltop rebroadcasters use frequencies in bands shared with both fixed and mobile military services within the limits shown. I donít know the exact upper and lower limits of the bands used for the VHF and UHF links, but the approximate band edges are given below.

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. I now find out in 2011 these were four of the five transmitters on the Region 9 Principal Net. which covers the area where I live.

Network Design

MOULD Hilltop sites

Example of Mobiles accessing MOULD Network

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 to give area coverage. 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.

Hilltop Site Control Unit Logic

MOULD Hilltop Control Unit Logic

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 sent out on all the other links except the originating link.

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.

Insertion Vehicle and Support

MOULD Insertion Vehicle exterior

Courtesy of M a r t i n   S w i f t.

Radio Installation inside the Insertion Vehicle

MOULD Insertion vehicle radio installation

Courtesy of M a r t i n   S w i f t.

The Emergency Services radio schemes had all their basestation and link transmitters and receivers duplicated. This was not the norm for MOULD except at the more remote hilltop sites where link radios and rebroadcasters were duplicated as access could be difficult in adverse weather conditions. To guard against the loss of a hilltop site, due to wartime action or a fault, mobile units known as 'Insertion Vehicles' were available that could be driven to the site to replace it while repairs were undertaken.

The Insertion Vehicle is the hardtop Landrover with a supporting stores vehicle and generator. It contains the same sort of equipment used in the hilltop installation. The radios are channeled up to allow them to replace any of the MOULD hilltops within the Region it supports.

Phase 1 Mobiles

Region 2, M252 Channels

CH     NET            SITE
 1 Principal (N)  Trimdon
 2 South Yorks    Clifton
 3 Principal (N)  Colliers Law
 4 Principal (N)  High Spen
 5 Principal (N)  Richmond Outmoor
 6 Principal (S)  Clifton
 7 Principal (S)  Golcar
 8 Principal (S)  Ravenscar
 9 Training Net   Richmond Outmoor
10 Principal (S)  Weedley
11 Principal (S)  Garrowby Hill
12 Durham         Trimdon
13 N Humberside   Weedley
14 N Yorkshire    Garrowby Hill
15 Northumberland High Spen
16 N Yorkshire    Richmond Outmoor
17 Region 2 MIV
18 - Spare -

The previous topic described the basic network design. In Phase 1, Mobiles and outstations had 18 channel Pye M252 radios. In this example for Region 2, The radio has a choice of hilltop sites to operate through, four on the North Principal Net and five on the South Principal Net. A choice of two sites for North Yorkshire but only single sites for the remaining County Nets. Channel 17 is in reserve should a Mould Insertion Vehicle (MIV) need to be deployed.

The Full Details - An Example from Region 8

Site and Radio Link Map

MOULD Region 8 Radio Scheme with radio frequencies

Click Diagram for Frequencies and Locations

In Wales there were two Principal Networks, Region 81 in the North and Region 82 in the South, corresponding with Brackla RGHQ 82 and a nonexistent RGHQ 81. 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 Gwent and Powys 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 networks for Region 10 Principal, Cheshire and Merseyside. Similarly Brown Clee is located in Region 9 has other rebroadcasters for Shropshire and the Region 9 Principal Network.

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 set with its 250 channels had sufficient to cover the whole country. Some of the rebroadcasters on this map use the same frequencies but they are sufficiently well separated to avoid interference.

Overview of all the other Home Defence Regions (1 - 10)

At the foot of this page is a link to a further page giving a Regional Map of sites showing the radio links between them. It lists the networks and the hilltops used to access those networks. There is a historical list of rebroadcaster transmit and receive radio frequencies on that page too.

Civilian Use of MOULD

MOULD Aerial

MOULD Aerial

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 public 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.

Feedback - Dave W has kindly supplied this extra information about the aerials

These antennas were available commercially and are used extensively in 2-way radio systems including those implemented at bus depots, taxi operators, farms, water companies, shopping malls and any number of other users.

These antennas were available in various frequency range variants, in different physical lengths. They were made by Telecommunications Limited of Dublin Ireland which eventually became Sigma prior to closure following a buyout of the antenna business of Sigma by American PCTel in recent years.

TCL/Sigma was a feeder factory for Pye Telecom/Philips Telecom/Simoco Europe for many years. These antenna types were used extensively by their service division for many many years, in installations at commercial customers premises as well as Government.

These antennas were neither unique to MOULD, nor were they the only type of antenna to be used on the MOULD system. They were and still are exceptionally efficient omni-directional vertical antennas (hence perfectly suitable for Defence Communication Systems), I still use them today and it is inconvenient that they are no longer being manufactured. The green upper section is made of fibreglass and incorporates an end fed dipole with an aluminium base.