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Perhaps the best way of showing the progress of the vehicle restoration is through a series of photographs.
The Trustees of the Broadcast Television Techology Trust would like to thank James Thorpe, director of Chiltern Automotive, for his dedication to the MCR21 Project through very difficult times.
Volunteer, David Thompson, shows off the new paintwork
Harry Coventry, senior cameraman on MCR21 in the 1960s,
inspects the restoration work

With the restoration of the vehicle nearly complete, it will soon be time to start re-installing the broadcast equipment.
          1976 - LO21 in Cherbourg for a Seaside Special programme.

During 1969 MCR21 was converted from a 4-camera monochrome unit to a 2-camera colour unit taking on the designation, LO21, with the LO standing for London. After  LO21 finished service with the BBC in 1977, there were another three units which were given the number LO21. These units, like the first LO21 were smaller units compared with the multi-camera mobile control rooms which were based at the BBC's London OB base,  Kendal Avenue.
In 1969, MCR21 was equipped with two Philips PC60 cameras that had come from the Presentation A studio at Television Centre when it became known as LO21.  The PC60s were replaced with two EMI 2001 cameras, making it compatible with the main fleet based at Kendal Avenue.

            Below left  an EMI 2001 camera   Below right a PC60 camera     

The second incarnation of LO21 was bit of mystery OB unit. Originally called  the 'Twin Channel Unit' witth the reg. no. PYL 697R, which suggests that it was in service with the BBC by 1976. That is just around the time the original LO21 was taken out of service. So far no photos of this second LO21 have been discovered.

By early 1981, the third LO21 had arrived at Kendal Avenue. This unit was originally equipped with two LDK 5 cameras, and again become a useful addition to the fleet, covering small OBs or when extra cameras were needed for very large and complex OBs
The third LO21 at Putney - helping out with the coverage of the Boat Race

Below right  - The same LO21 at Admiralty Gate for the wedding of Prince Charles and Diana
Below left -  a Philips LDK 5 - these were later replaced by a number of smaller cameras.
At the beginning of the 1990s, Sony built five mobile control rooms for the BBC - the type 7s. Two units were allocated to Kendal Avenue with one of them took on the designation LO21, the fourth in the series. These units were equipped with  Sony 370 cameras - originally four but could handle six cameras - allowing the unit to be used on quite complex outside broadcasts.
Information - Brian Summers

By Philip Upton
Everyone with an interest in Outside Broadcasting is aware of the existence of Mobile Control Rooms, of which MCR21 currently being restored, is a prime example.  What  seems to have been forgotten is how the 'output' (i.e. the pictures and sound, as selected by the Director in the MCR) found its way into the BBC national network and thence to the transmitting stations for broadcast. Sound was usually sent via Post Office lines, which were more or less telephone lines suitably tweaked (equalised) to provide better quality. (Get used to the expression PO as it features a lot in this article. We know it now as BT but in those far off days, it was indeed the PO, a government department, which delivered national communications, along with letters and parcels!)
The vision signal from the MCR was a different matter.  In these days of umpteen video circuits whizzing round the world in digital form via optical fibres and satellites, it is often forgotten that the transmission of a single 405 line black and white TV signal, in analogue form, back in those days was a formidable task.  It was even trickier for 625-line colour.

Before we get on to OB signals it is worth reminding ourselves that video circuits generally were few and far between, especially those incoming to TV Centre for onward transmission, known as “Contribution Circuits”.  There was, for example, a single circuit running down the spine of the UK, starting in Aberdeen I think but which routed through BBC centres such as Edinburgh, Glasgow, Manchester and Birmingham.  The circuit was hired from the PO and cost a fortune. Other regional centres had similar arrangements. As an aside, for those who remember such things, and pardon the jargon, the source Synchronising Pulse Generator  had to be phased or “Genlocked” to the Television Centre SPG to prevent a frame-roll when presentation cut to the next source.  This applied to all sources outside TVC, be it a regional studio or an OB.  (A further aside - TVC had a huge network of video cables going up and down between floors so that video from all sources was synchronously timed on arrival at the central apparatus room).
So how did the MCR video get to TV centre?   Many of the regularly used OB locations in the central London area had access to cables, but it was a different story for OBs originating elsewhere and the usual method was the establishment of a temporary Radio Link using a dedicated fleet of vehicles and extending towers.  The very earliest links used Band 1 frequencies - large Yagi aerials similar to those on people’s houses, used for picking up broadcast TV.  It was soon realised that microwave frequencies (known universally as SHF) were more appropriate, bearing in mind the relatively large bandwidth an analogue video signal occupies and, by international agreement, a group of frequencies, known as “the private user band” was allocated. Initially this was around 4GHz but later the 7GHz band was used widely and eventually an 11GHz slot was allocated.
So, what happened on the ground?  During the OB rig, at some point, one of the OB crew would present two co-axial cables to a nearby 'Links Van'.  These carried the MCR video output, two being offered as main and standby.  These were plugged into sockets in the Links Van and via various monitoring and switching arrangements, the video modulated an SHF transmitter, the business end of which was mounted behind a dish aerial usually 4ft in diameter and sometimes mounted on a tripod on the van roof.  More often, bearing in mind that many OB’s originated in built-up areas, the transmitter and dish were mounted on an extending tower. Most of these  'Eagle Towers' were made by Eagle Engineering of Warwick.  They were 60ft high and were the backbone of OB Links for years.  There were two 100ft Merryweather fire escape ladders in the London OB fleet.  They were of pre-WW2 design and could only carry a small dish, 2ft in diameter.  These ladders were replaced by 100ft Eagle Towers in the early 1970’s which carried a much larger head-load, up to two 4ft diameter dishes.

Above- Two of the original Eagle Towers which could reach. The right hand picture, and the one below, show the 1970s Eagle tower, which extended to 100t high.
The links unit at the OB point was always called 'The Starter'.  Sometimes it would fire its signals direct to a similar dish with an SHF receiver attached and mounted on another links van.  This would decode the SHF back to video which could be fed into an access point on the BBC contribution network. Such a link was described as a single 'hop' and although occasionally used, a direct line of sight from Starter to the final Receiver was often not available.  In that case one or more 'mid-points' had to be established on suitably located hill-tops.  At a  mid-point two dishes were needed, a receiver and transmitter to relay the SHF signal to the final receiving van located at the eventual network access point. Two hop circuits were very common but occasionally long routes required several hops. 
There was a major Links Unit based in London (first at Wembley, then at the West Acton OB base) and each regional OB base had a unit each with four Links Vans and one Eagle Tower.  (These were at Bristol, Cardiff, Birmingham, Manchester, Glasgow and Belfast).  In practice each unit acquired, through experience, a number of favourite mid-point locations, but when a new OB location came along a new route had to be worked out and it was always tested by setting up the proposed circuit to prove its performance, sometimes weeks before the OB date.
Final receiving points where the incoming signal could be injected into the BBC contribution network were many and varied, but one always hoped that the final hop could be routed to a main BBC broadcast transmitter.  Each of the principal masts had a remotely steerable SHF dish at its summit, connected to a permanent receiver in the transmitter hall.  They were known as Mast Head Receivers (MHR’s).  The beauty of this arrangement was that the final hop could be very long due to the height of the receiving dish, and the system removed the need for a links van at the reception point. At each of these broadcast transmitter sites there was, of course, an incoming vision feed of 'Network' for the broadcast signal but it was usually coupled with a circuit in the opposite direction for contributions.  These were usually PO circuits, although there were a few quirks in certain parts of the country.  The MHR’s had another function in many locations, receiving the video output from secondary regional studios, such as Southampton and Plymouth, each of which had an OB SHF transmitter on the roof.  (All my operational experience was in West Region, before I went to TPID to work on fixed links, new radio links vehicles and extending towers)
If a route to an MHR was not feasible another injection point was needed.  London bound PO circuits went through repeaters at telephone exchanges, and could be intercepted.  In Bristol we rented a room at the very summit of a decorative turret which formed part of a Bristol University building known as 'The Royal Fort'.  We used to operate a very long distance two-hop link from the Shropshire area, i.e. the 'Starter' at the OB location, a 'Mid-point' on the Worcester Beacon on the Malvern Hills, final Receiver at Royal Fort, then a PO co-axial cable into Bristol BBC switching centre, thence via the Bristol permanent contribution circuit to TVC.
There was also a major receiving station at Swains Lane in Highgate with permanent dishes on a small mast which was, I believe, originally built by the RAF.  A vision circuit from Alexandra Palace to London switching centre at BH had a repeater amplifier housed there and so the OB signals could be injected.
Setting up these circuits was a big undertaking and offered a greatly varied and adventurous life.  Mid-points could be very challenging, requiring the links van and a long wheelbase Land Rover each towing a diesel generator to provide (main and standby) power.  Access could be tricky, with steep climbs and muddy tracks.  Originally, domestic facilities in the links vans (you could be there for several days) consisted of an electric kettle and toilet facilities were in the nearest bush.
But the views were, by definition, tremendous and I personally never lost the thrill when London Presentation announced to the nation that the next programme would be 'our” OB and the video passing through our van  popped up on our domestic telly in the links van.
In the late 1960’s a fashion developed for contest programmes involving teams from different parts of the country, notably 'Come Dancing' (No! Not Strictly!) and 'Top of the Form' – a contest between schools.  If these were live then each end of the programme had its own OB link as usual, and each team could observe the opposition by watching TV on a domestic telly (as broadcast).  However, at that time video recording was maturing and some producers elected to record the programme.  This involved setting up a 'reverse vision circuit' so that each team could see their competitors.  These could be a nightmare – MHR’s could not transmit and occasionally the outbound and inbound routes had to be quite different.  Mid points involved two links vans and four dishes.  Often there were two Eagle towers at the starter.  Imagine a contest between schools in, say, Aberdeen and Plymouth and the number of hops, hill-tops and dishes that might involve.  (Although of course, the backbone of the circuit would be one of the fixed contribution routes).   Links units also had a few peripheral duties such as OB radio mikes and we had a VHF short range capability for links from boats and moving vehicles – but that’s another story.
I was project manager for the design of a new range of links vehicles introduced in the late 1960s. It coincided with introduction of the first 'solid state' SHF equipment which could be battery powered, reducing reliance on a diesel generator.  I also introduced a wash-basin and bottled gas heating.  (What a hornet’s nest that stirred up with the BBC insurance manager !) Incorporating a 'two room' layout to keep the domestic and technical area clean and separate from the storage of cables, dishes and tripods, it was not a popular design.  I also produced the two 100ft Eagle towers mentioned earlier which replaced the ageing Merryweather fire escape ladders.
Eventually, all this became totally redundant with the advent of digits and the resultant availability of communication satellites and optical fibre circuits.  We are all familiar now with the small 'Satellite Trucks' with a single remotely controlled dish on the roof.  The compact design of modern electronics and above all the digital process made these possible.  OB planners and news departments can now order these circuits, often at very short notice,  from a multiplicity of operators via a few clicks on a website.
Gone are the weeks of planning, pouring over Ordnance Survey maps, muddy wellies, temperamental diesel generators and mislaid van keys and all the other the other things which had to be solved so that the licence payers could  watch their favourite sport, party political conferences and the rest. I loved it !

How did  BBC TV OBs get their pictures and sound
back to the Transmission Suite?
Nick Gilbey
with information and photos from Mike Steed, Mike Jordan,Phil Upton and Dan Cranefield
This map shows the original cable (the black line)  which was laid in 1936 in time for the coronation of George VI in April the following year. In simple terms, it was a dedicated telephone line which went to Broadcasting House then on to Alexandra Palace. The BBC just televised the Coronation Procession at Hyde Park Corner. The BBC did have their transmitter van and aeriel tower as backup should the landline failed. Sending signals back to Alexandra Palace did have a disadvantage, in that the transmitter at A.P. could affect the incoming signal. This was solved by setting up a receiving station at Swains Lane in Highgate, just a few miles away from A.P.  Swains Lane remained a receiving point for television outside broadcasts well in the 1990s
Inside Swains Lane in 2019 when the decommissioning had started.

The photo shows the control desk, designed by BBC engineering project manager, Mike Steed, in about 1980. At that time, Swains Lane was becoming very busy handling more and more feeds from outside broadcasts - sometimes taking in four feeds simultaneously from around the London area. This control desk replaced one that had been installed a decade earlier by the then project manager, Philip Upton.
You can see the five receiving dishes on the tower - one on the very top and four in between the two static dishes. The OB receiving dishes could be rotated through 360 degrees from the control room below.
In central London there was no need to use a microwave link from most locations. In the 1960s the Post Office put in a comprehensive network of coaxial cables which replaced the telephone lines.
Above - a map showing the connections to the London coaxial cable.
Below - the connection at Downing Street
In 1975 the BBC used a satellite link to get pictures back from an outside broadcast covering a mountain climb at Glencoe in Scotland. It was an experiment so there was  also  a microwave link which had many mid-point to get the pictures back to base. It would be nearly another twenty years before satellite trucks  became the norm for links between outside broadcasts and the studio base.
Satellite city in 2011 at Buckingham Palace for Prince William and Kate's marriage. Apart from a few local microwave links to remote cameras, the BBC, who were the host broadcaster, used fibre cable to connect the outside broadcast units which lined the procession route.
The satellite trucks were used for the national and international news networks which had descended on London for the wedding.

While satellite communication links from outside broadcasts continued to grow during the 1990s and 2000s, microwave links were still being used to connect remote cameras back to the mobile contol rooms. Below is a comms diagram for the links used by the BBC outside broadcast unit which covered the arrival in February 2005 of Ellen MacArthur's yacht at Falmouth, after her epic
Round the World single-handed sailing voyage.
The remote unit at Pendennis Point with the micrwave, satellite and UHF links
Above  - A Post Office  Television Outside Broadcast Service van. These vans were seen at nearly every television OB in central London, connecting the outside broadcast to the cable network under the streets of the city.

Below  2014 -  a one-day cricket match broadcast  by Sky in Bristol
This time a BT van connects the output from the CTV  outside broadcast unit to the fibre cable network and, using a dedicated IP address, gets the signal back to Sky HQ at Isleworth
ITV also used Post Office cables under the streets of London to connect to their transmission suites. For Rediffuion, this was in their studio complex in Kingsway, Holborn. The photo above shows an ATV control room next to the Post Office van. For Sir Winston Churchill's Funeral, ITV's coverage was directed from Studio 9 at Kingsway. Extra lines had to be installed by the Post Office along the procession route in order to connect the many ITV mobile control rooms back to the studio.

For OBs away from central London, Rediffusion had a fleet of four short wheelbase landrovers, which carried microwave equipment in order to transmit the signals back to a receiving dish on top of a water tower at Campden Hill near Notting Hill Gate - not quite as comprehensive as the facility, which the BBC had at Swains Lane

Brian Summers
The BBC designed this mixer in 1962 for installation into the ten new Pye TVT built  4-camera units MCRs 19 to 28, which were delivered to the BBC between 1963 and 1964. The vision mixer has ten input channels, six are for synchronous sources and four can be switched to sync or non-sync. Cuts, mixes, wipes, inserts, and split fader operations are possible. For the first time this is a fully solid state mixer using transistors and diodes as the switching elements. Relays and solenoids are used for the bulk of the controlling logic. The design was  advanced for the time, other manufacturers were still using relays for all the switching elements. The design was adapted for colour working and was installed in a further twelve BBC outside broadcast mobile control rooms. The mixer was also used in many studio installations including the BBC News studios at Television Centre.
The vision mixer in the BBC Type 2 Colour Mobile Control Room, which was in service with the BBC until the early 1980s. Now owned and beautifully restored by Steve Harris.

Paul Read continues his work restoring the monitors which will be installed in MCR21
Watch Paul's Video
Watch Paul's Next Video

We have received generous donations from individuals and companies.
The restoration still has a long way to go before it is complete. MCR21 will then have a role in explaining the technology used in the broadcast television industry. Our aim is to attract young people into the technology side of the industry.

We would welcome supporters of the MCR21 to become

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or telephone Nick 07831 219957

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Newsletter compiled and edited by Nick Gilbey
Thank you to William Brown, Andrew Brown, Harry Coventry, Steve Harris, Paul Read, Ian Hayes, Rob Burn, Philip Upton and Brian Summers for information, photos and help.
Newsletter August 2020
Newsletter May 2020
Newsletter March 2020
Newsletter January 2020
Copyright © November 2020 Broadcast Television Technology Trust,
All rights reserved.

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MCR21 · The Abbots House · The Street · Charmouth, Dorset DT6 6QF · United Kingdom

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