Rediffusion installed a Wired Vision Network to serve the City Of Leicester in the early 1960’s. The author of this article worked on the Network between 1973 and 1990, so it is the architecture of the Network over that period which is discussed. The Wired Vision Network survived until the late 1990’s, but with such a limited capacity (a maximum of 6 television channels), it was eventually closed down because of it’s inability to compete with the modern Broadband Cable Network which was installed across the whole City between 1990 and 1995.
The Rediffusion operation in Leicester was based at their main office location at Malabar Road on the St Matthews Estate. As well as a Showroom and Payments Centre, the offices were also home to the Service Office, TV and Equipment Workshops, Stores and Administration. The photograph below shows the office building as it looks today.
There were also Showrooms and Payments Centres at Belvoir Street, Narborough Road and Uppingham Road in Leicester, plus at Hinckley Road, Earl Shilton and Castle Street, Hinckley. The Showroom in Belvoir Street was moved to a more central location at EastGates opposite the Clock Tower in the City Centre.
In the early 1980’s, the Rediffusion Operation was split in two. The TV and VCR Sales and Rental Business was sold to Granada and all Staff associated with this area of the business transferred to Granada’s Service Centre in Leicester. Also all Showrooms were transferred to Granada ownership. Only the Showrooms at Eastgates and Castle Street in Hinckley were retained under the Granada name, all other Showrooms were closed.
The Cable Operation was rebranded as Rediffusion CableVision and was later sold to Robert Maxwell’s Mirror Group. The Cable Operation was far too small to continue to occupy the building at Malabar Road, so around 1986 they moved to a smaller office building on Commercial Square at Freemen’s Common.
Following the move to Freemen’s Common, the company was first of all rebranded as British Cable Services, then later becoming Maxwell Cable TV.
The Wired Vision Network
The Wired Vision Network was primarily designed to be received and watched on Rediffusion’s own Cable TV Sets, with no tuner, channel selection was made by turning a rotary selector switch. Rediffusion also rented out loudspeakers to receive radio programmes, again using the channel selector switch to change channels. Rediffusion also supplied an Inverter to Council and Housing Association Tenants, which converted the output of the rotary switch to a UHF signal so that conventional Aerial TV’s could be connected to the network. The service to these tenants was known as the Rediffusion Community Service, or RCS for short.
For many years a 6 channel system was maintained, with 3 television channels, BBC1, BBC2 and ITV, plus BBC Radio’s 2 and 4, plus BBC Radio Leicester which was of course the first ever local BBC radio station. When Channel 4 Television commenced, it replaced BBC Radio Leicester during transmission times.
The Wired Vision Network was for many years installed overhead, with cables and junction boxes attached just below gutter height. With later installations the cables and junction boxes were placed below ground or in ground level junction boxes.
As well as the Wired Vision Network, Rediffusion did also install and operate Master Antenna TV (MATV) systems. These systems were generally remote from the main Wired Vision Network, and were therefore fed from their own antennas. They were typically UHF systems, although some were VHF systems with distribution via co-axial cable. The VHF systems required an up-converter called a Superverter between the aerial socket and the customer’s TV to up-convert VHF signals to UHF so they could be received by a conventional UHF TV set. An example of a MATV system was the development on Ethel Road with the antennas on the top of the block of apartments known as Carrick Point.
The Aerial Site
Situated at Western Park Farm, the Aerial Site was the “Head End” of the Network. With a 100ft antenna tower, off-air television and radio signals were received and processed here for onward transmission, or “Rediffusion” across the City. The Photograph below was taken in the early 1960’s and shows the Aerial Site soon after it was completed.
Each television channel was received and processed by an FC100, a device with a UHF Tuner for channel selection, with separate sound and vision outputs. The vision output from the FC100 was a signal known as HF (High Frequency), in the early days using 2 modulation schemes, either 5.9MHz vision carrier with upper sideband transmission, or 8.9MHz with lower sideband transmission. In later years, the 8.9MHz modulation scheme with the addition of an FM audio carrier at 2.9MHz was adopted on all channels, the reason for this is explained in a later section “The Arrival Of The VCR”. The vision signals were amplified at the Aerial Site before being distributed across the City via the “Vision Trunk Route”, consisting of up to 6 co-axial cables each cable capable of carrying 1 television channel’s video content.
The audio output from the FC100 was a baseband audio signal, amplified by huge valve amplifiers in the early days, to levels as high as 550v before being distributed across the City via the “High Level Link”. This consisted of a number of 18swg copper pairs, with 2 pairs per cable in a quad configuration. At the Distribution Kiosk, the Audio was transformed down to “Service Level” at 55v for distribution onto the local network, as described in section “The Distribution Kiosk”.
The radio channels were also received and transmitted from the Aerial Site. These were received on conventional FM Tuners with baseband audio outputs once again amplified by valve amplifiers to as high as 550v before being distributed across the City via the “High Level Link”.
In later years, due to the demise of the valve, the audio for both television and radio channels became amplified by transistorised amplifiers, with the maximum voltage carried over the “High Level Link” reduced to around 350v. The transistorised amplification of the audio signals is explained further in the later section “The Substation”.
The housing developments at Beaumont Leys and Anstey Heights on the North West edge of the City Of Leicester gave Rediffusion the opportunity to install a brand new network with additional capacity, and a new 12 channel system was installed with potential to carry 6 Television and 6 Radio Channels. This development came along at the time when Sky Television and other satellite services were getting established, which meant that there was an opportunity to offer a mix of terrestrial off-air and satellite channels. Hence a Dish Farm was installed next to the Antenna Tower at Western Park, and Satellite Receivers were installed. The 12 channel system is detailed later in this article.
Although the Wired Vision Network has long since gone, the Antenna Tower is still in use today by a Mobile Phone Operator, although the original pre-fabricated building has been replaced by a more substantial brick building.
The Trunk Network
Consisting of the Vision Trunk Route (VTR) and Audio High Level Link (HLL), the primary Trunk Network ran entirely underground, and mainly followed the route of the railway lines through the City. The VTR required amplification at repeaters every few hundred yards, but the HLL was only amplified at the Substations at Saffron Lane and Forest Road as described later.
From Western Park two spurs fed to the north and east to feed Glenfield and New Parks. The main Trunk joined the railway line at Hinckley Road close to Winstanley Drive, with a spur going off along Hinckley Road and along towards Fosse Road North to feed the Newfoundpool and Groby Road areas. The onward feed ran south along the railway before dropping down into Westcotes Kiosk adjacent to the railway bridge on Narborough Road. Westcotes Kiosk was the first repeater on the VTR.
From Westcotes Kiosk, the Trunk continued south along the railway line before reaching the Saffron Lane Substation adjacent to the railway bridge, close to the Aylestone Road junction. Both vision and audio signals were amplified here, as described in the later section “The Substation”.
2 Trunks left Saffron Lane Substation, one heading south along Saffron Lane to feed Knighton Fields, Aylestone, Saffron Lane Estate and Eyres Monsell Estate. The other Trunk continued on along the railway for a short distance before crossing the Industrial Estate at Freemen’s Common, with a spur going off towards Clarendon Park. The main Trunk continued through a thrust-bore above Knighton Tunnel to rejoin the railway line in a northerly direction towards Leicester Station.
At the railway bridge at Lancaster Road, another VTR repeater amplified the vision signals. A spur then went off to feed the area around the Royal Infirmary and the City Centre. The Trunk continued along the railway with a spur just north of the railway station to feed St Peters, Highfields and St Matthews. The onward feed continued along the railway to another VTR Repeater at Vulcan Road before continuing along to the Substation at Forest Road.
At Forest Road Substation, vision and audio was again amplified. 3 Trunks left the Substation, the first continuing along the railway to feed Northfields and Rushey Mead. The second going along Ulverscroft Road to feed St Marks, Belgrave, Abbey Lane area, Stocking Farm and Mowmacre Hill. The final Trunk fed along Brighton Road and out of the City along Uppingham Road and Scraptoft Lane, to feed New Humberstone, Rowlatts Hill, Netherhall and Thurnby Lodge.
The Substations at Saffron Lane and Forest Road were only used to amplify Vision and Audio signals for onward transmission on the Vision Trunk Route (VTR) and High Level Link (HLL). No local cable networks were fed directly from the Sub Stations. In the early days, valve amplifiers were used to amplify both Vision and Audio signals. Whilst the Vision Amplifiers used fairly small valves, the Audio Amplifier valves were much larger as seen in the photograph below. The audio amplifier for just one channel was 6ft tall by 2ft wide and 2ft deep.
By the late 1970’s, all valve amplifiers had been replaced by transistorised amplifiers. The transistorised vision amplifiers, designated the AR107T amplified the incoming VTR to an 8.9MHz carrier level close to 3v.
The valve amplifiers raised the audio levels on the HLL to around 550v. With the introduction of transistorised amplifiers, this level was reduced to around 350v. This was transformed down at the Distribution Kiosk to Service Level at 55v to feed directly into the Cable Network.
The introduction of transistorised audio amplifiers enabled the audio amplification to be moved out to the Distribution Kiosk. The audio amplification was achieved using an AA106 pre-amplifier for each channel. Each AA106 then fed a bank of 5 or 6 x AA105’s, the outputs of which were connected in parallel to drive into the HLL. In addition, a single AA105 for each channel was used to drive lower audio levels of 55v at launch to be operated from the Sub Stations into the trunk network, via smaller multi-pair cables, this was known as the Service Level Link or SLL. The SLL was used to drive into Distribution Kiosks which had their own local audio amplifiers. As the SLL sections of the Trunk Network ran at lower levels, this meant that additional intermediate amplification was required in part of the Trunk Network. Therefore, a smaller Sub Station for audio amplification was installed at the main office location at Malabar Road. This smaller Sub Station was relocated to Freemen’s Common when the Malabar Road building was vacated.
It was necessary to maintain both HLL and SLL from each substation as a small number of Distribution Kiosks did not have their own local audio amplifiers.
The Substation at Saffron Lane has long gone, but the building at Forest Road is still there today, and is used by a Building Supplies Company.
The Distribution Kiosk
The Distribution Kiosks were either metal with roller shutter doors, or brick constructions with either lift-off or hinged wooden doors. Some were also installed in what looked like a brick- built garden shed. Most of the original kiosks are still in place, as can be seen from the photographs below. The metal shuttered kiosk shown is the old Newfoundpool Kiosk on Stephenson Drive, the brick example is the old Aylestone Kiosk on Wigston Lane.
The purpose of the Distribution Kiosk was to combine the audio and vision signals onto the multi-pair Cable Network, amplifying them as necessary for onward distribution. Audio and Vision signals were carried together on the Cable Network, only being split again within the customer premises. The early Kiosks had no local audio amplification, so the audio was transformed down off the 550v HLL to 55v Service Level for onward distribution. A gradual upgrade programme saw most, but not all Distribution Kiosks have local AA105 audio amplifiers installed. Vision amplifiers not only amplified the vision signals, they also converted the incoming unbalanced signals from the VTR to balanced signals to be fed into the balanced Cable Network.
The vision signals were amplified at every Distribution Kiosk, sometimes just to feed the local cable network, but sometimes to amplify the ongoing vision signals on the Vision Trunk Route (VTR). Four types of vision amplifier were used as follows:-
AR106 - 14v Vision Output feeding local cable network only.
AR107 - 14v Vision Output feeding local cable network, plus 3v Vision Output feeding ongoing VTR.
AR113 - 28v Vision Output feeding local cable network only.
AR114 - 28v Vision Output feeding local cable network, plus 3v Vision Output feeding ongoing VTR.
The Repeater Kiosk
To extend the serving area of the Distribution Kiosk, repeaters were installed in some areas of the network. These provided a pass-through for the audio signals, but provided amplification for the vision signals using either AR106 (14v O/P) or AR113 (28v O/P) vision amplifiers. These Repeater Kiosks had a mains power source, but were never battery backed up. The photograph below shows a typical Repeater Kiosk, the location of this roller-shutter type one is unknown. Some Repeater Kiosks were brick-built with lift-off or hinged wooden doors.
The Transistor Repeater
In some parts of the cable network, small line-powered Transistor Repeaters were installed to further extend the serving area. These repeaters were line-powered from a “Phantom Power Supply” installed within the Distribution Kiosk. This injected a 50 Volt AC supply into the network to provide remote power for the Transistor Repeaters. These provided a pass-through for the audio signals, but provided amplification for the vision signals using A619A (2.9v O/P) vision amplifiers.
The Transistor Repeaters were housed in a small metal wall-mounted enclosure, approximately 15” square by 3” deep. They were generally installed at half-section ladder height for easy access.
The Wired Vision Network
The Distribution Network used a “Tree and Branch” type architecture. The basic concept of this architecture is to run out several trunk cables from the Distribution Kiosk, then spur off smaller distribution cables onto which subscriber’s drop cables are connected. Generally no subscriber drop cables should be connected to the trunk cable, but in practice they often were.
Where the Wired Vision Network was installed on 100% of the homes in the serving area, which was the case on the Council Estates, spur boxes could be logically placed at the end of the street or row of houses. This made fault finding a great deal simpler. However where the network extended on to private dwellings, wayleaves had to be obtained to allow cable plant to be attached. This meant that a relatively small percentage of homes had network attached, spur boxes were placed wherever they could be installed, hence the network was more difficult to service in these areas.
The Distribution Network used multi-pair copper cables, each channel carried on a separate balanced pair of wires, and on the same colour throughout the network, so for instance Channel 4 was always carried on the green pair of wires. The early network was built using 6 pair cables, each pair of wires capable of carrying 1 television channel. Later 9 pair cables were introduced with 6 vision and 3 audio pairs, finally 12 pair cables were introduced with 6 vision and 6 audio pairs. As the Distribution Network spread out from the Distribution Kiosk, higher signal levels were carried on larger gauge copper wires, with the size of gauge reducing as the network spread further out from the Kiosk.
Trunk cables consisted of larger gauge copper wire, with 20swg copper used for the vision pairs, and 24swg copper used for the audio pairs. These trunk cables also contained a copper screen, which needed to be bonded to earth to prevent ingress from stray RF signals. The distribution cables consisted of 22swg copper wire for the vision pairs, and **swg copper wire for the audio pairs. The subscriber drop cable consisted of 26swg copper wire for the vision pairs, and 27swg for the audio pairs.
The Trunk Cables ran out of the Distribution Kiosk to the Spur Box. Inside the Spur Box, signal splitting devices called Spur Inserts were installed to split the vision and audio signals. These Spur Inserts contained small transformer devices encapsulated in a clear resin, and provided a point at which signals could be tapped off to feed along distribution cables, with different side loss values available depending on the distance the signals had to travel along each spur of the network. Spur Inserts were available with side loss values of 20dB, 13db and 8db, with a through loss of between 1dB and 2.5dB to feed onwards along the Trunk Network. The final Spur was a simple 2 way splitter with a 3dB loss to each leg. The network was carefully planned to ensure that sufficient signals were available to feed the subscriber drop cables at the end of each spur.
The subscriber connection was made at the subscriber junction box, or sub’s box. Within the sub’s box, a subscriber insert was connected on to the distribution cables without breaking them, with the electrical connection being made using a serrated washer under a slotted screw to cut through the insulation and clamping down onto the copper conductor. The subscriber’s drop cable connected to the insert by being trapped against a small metal peg using a small push-on eyelet, stripping the insulation and making an electrical connection at the same time. The Subscriber Insert was available with loss values of 28, 23, 28 and 13dB. Each value of subscriber insert was available to accommodate either 2 or 4 drop connections.
The 12 Pair Wired Vision Network
In the early to mid 1980’s, a massive new housing development was built on the north west side of the city, between the city and the village of Anstey. This was a mixture of council and private housing, the council development became known as Beaumont Leys, and the private development became known as Anstey Heights. This gave Rediffusion the opportunity to install a more modern Wired Vision Network, using 12 pair cables throughout. The 12 pair cables were capable of carrying 6 TV and 6 radio channels.
A new Trunk Route was built to feed the new development directly from Western Park Aerial Site. Initially only 4 TV and 5 radio channels were carried on this network. Then later, 2 satellite channels were added, one free and one subscription service. So the free service was Sky Channel and the subscription service was the movie channel “Premiere”. To enable these services to be received, a small dish farm was installed adjacent to the Antenna Tower.
The Customer Premises Installation
The Drop Cable was generally taken into the customer’s home through the wooden window frame, with the Channel Selector switch often fitted to the window ledge. Early selector switches had screw terminals to make the electrical connection, but the later SW101 switch used the same push-on eyelet connection as the sub’s insert. The SW101 was a 12 position selector switch, used to change channel, with the channel positions marked with the letters A through to L.
If the Customer had a Rediffusion Cable Set, a flylead was connected between the selector switch and the rear of the television, with an 8-pin “octal” plug to connect to the rear of the television. It was within the octal plug that the vision and audio signals were finally separated.
In installations within City Council and Housing Association premises which were supplied with service as part of the Rediffusion Community Service (RCS) agreement, it was possible to connect UHF Aerial TV’s to the selector switch by using a device called an Inverter. The Inverter took the incoming vision signal at HF and up-converted this to UHF for connection to the aerial socket. A single tuner button was then tuned to the UHF output of the inverter, with channel selection made by turning the selector switch to the appropriate channel. The audio had to be wired directly to the television’s loudspeaker using an audio cable from the inverter, cutting the lead to the loudspeaker which made the television's own volume control inoperable. Instead the volume had to be adjusted using a volume control on the inverter. This enabled reception of both TV and radio services on a UHF TV. Three types of inverter were used, the earliest was the IN106, next came the IN109, both these inverters were fitted with volume controls to adjust the volume on both radio and TV channels. Later the IN109A was introduced, this had no volume control, and was capable of receiving TV channels only (i.e. no radio).
The Arrival Of The VCR
The arrival of the domestic VCR presented a whole new set of problems to Rediffusion:-
Firstly, VCR’s could not be connected to a Cable TV Set, since these TV’s received the audio at 55v service level from the cable network, also the VCR’s video output signal was available either as an RF or baseband video signal, the Cable TV Set of course received the video signal via an 8.9MHz vision carrier. Secondly VCR’s could not be played on UHF TV’s which had been modified by cutting the internal loudspeaker lead. Thirdly one of the main benefits of the VCR was to be able to record one programme whilst recording a different channel, which of course is not possible if channel selection is carried out using a selector switch. Hence 3 solutions were required.
Solution 1 dealt with VCR’s connected to their own Cable TV Sets. Rediffusion had to develop an adaptor to connect between the VCR and Cable TV Sets. This took a feed from the cable network and up-converted the cable signals to UHF, and also converted the baseband video and audio outputs from the VCR to an 8.9MHz vision signal and 55v service level audio signal. This meant various types of video and audio connectors had to be available dependent on the type of VCR to be connected. To enable the VCR to receive and record TV signals, Rediffusion also had to add a 2.9MHz FM sound carrier to all TV channels from the Aerial Site which could be received by the VCR’s UHF tuner.
Solution 2 dealt with VCR’s connected to conventional UHF TV’s connected to the system via an Inverter. Once the 2.9MHz FM sound carrier had been added at the Aerial site, this was a fairly simple tuning process. This also required the UHF TV’s connected to the Network to have their audio output reconnected to the loudspeaker. This was mostly successful, although the odd UHF TV’s audio amplifier had failed and required the attention of a TV Engineer to effect a repair.
Solution 3 was by far the most complex from an installation point of view. This dealt with the ability to record one programme whilst watching another, this involved the installation of a dual selector switch called the SW111, and 2 inverters, one for the UHF TV and one for the VCR. This solution was also used for installations to Cable TV’s, but in this case the adaptor was connected to one switch and an octal flylead was connected to the other.
The Arrival Of The Remote Controlled TV And VCR
If the arrival of the VCR posed problems, the introduction of remote controlled TV’s and VCR’s proved a tougher challenge. The single or dual selector switch did not provide the ability to change channel by remote control. Hence the solution involved the installation of a “multiplex” inverter called an IN110, which filled most Service and Network Technicians with dread. This complicated inverter completely replaced the selector switch. Each drop cable pair connected to it’s own individual inverter module capable of outputting 1 x UHF channel. Either a 4 or 6 channel inverter was available, but these were never really very successful as the UHF output channels were never frequency locked together, causing horrendous patterning because of these UHF signals beating together. By luck rather than judgement, the installer could just about minimise these beats so that they were generally acceptable.
This one failing was probably the death knell of the wired vision system.
This article was written by Terry Wells. Terry has continued to work in the Cable Industry and now holds the position of HFC Architecture and Engineering Manager with Virgin Media, but remains based in Leicester
Leicester Rediffusion HQ (2008)
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Western Park Aerial Site 1968
Western Park Mast 2008
Western Park Cabin 2008
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Belvior Street Showroom 1968
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Aylestone Road Repeater Kiosk 2008
Newfoundpool Kiosk 2008
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An Overview of Rediffusion Leicester by: Terry Wells