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rb:coventrycable [04/05/2018 09:03]
andrew [Consumer Distribution]
rb:coventrycable [25/06/2018 23:37] (current)
andrew [Supertrunk]
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 ====== Coventry Cable TV ====== ====== Coventry Cable TV ======
 +
 +Now defunct, the original build was for 450MHz bandwidth carrying about 30 channels. It was built and operated by BT and along with the likes of Milton Keynes was one of the first franchises in the UK.
  
 ===== Headend ===== ===== Headend =====
  
 +Located at the end of Whitley Village, the building is now demolished.
  
 +
 +Satellite TV receivers & cable tv modulators and Launch Amplifiers.
 +
 +{{:​rb:​covcable-headend_.png?​200|}} {{:​rb:​covcable-launchamp.png?​200|}}
 +
 +Master Control room - monitoring all the channels being transmitted and some of the playout equipment.
 +
 +{{:​rb:​covcablemcr1.png?​200|}} ​  ​{{:​rb:​covcablemcr2.png?​200|}}
 ===== Supertrunk ===== ===== Supertrunk =====
  
-The Supertrunks radiated out from the Head End to distribution sites prior to feeding the local distribution network. These consisted of several amplifiers with one input and one output boosting the signal. The amplifiers were nothing special, just the same as the DLA amplifiers but run at lower gain (ie. less noise added to the signal), the supertrunk coax was about 2 inches ​in diameter for minimum signal loss. +The Supertrunks radiated out from the Head End to distribution sites prior to feeding the local distribution network. These consisted of several amplifiers with one input and one output boosting the signal. The amplifiers were nothing special, just the same as the DLA (Distribution Launch Amplifier) ​amplifiers but run at lower gain (ie. less noise added to the signal), the supertrunk coax was about 40mm in diameter for minimum signal loss. Due to the inflexibility of the low loss cable, the link to the cabinet was on reduced size cable with the joint in a chamber adjacent to the cabinet (left hand side next to road below) 
-These were located in smaller green fibreglass cabinets and were all line powered from either end of the trunk.+The supertrunk amplifiers ​were located in smaller green BT fibreglass cabinets and were all line powered from either end of the trunk.
  
 +{{rb:​20180519_115423.jpg?​400|}} ​ {{rb:​20180519_115350.jpg?​150|}}
 +
 +This cabinet seems abandoned, the door to this has been lying on the grass for several months.
 +
 +{{:​rb:​core1.jpg?​200|}} {{:​rb:​core2.jpg?​200|}} {{:​rb:​labelling-disc-spacing.jpg?​500|}}\\
 +This is the supertrunk cable, it is an aluminium core with a copper cladding (The aluminium will carry most of the AC line power, whilst the copper will carry the RF due to the "Skin Effect"​),​ the dielectric is polyethylene with air spacing to reduce loss but periodic "​Discs"​ of polyethylene to provide support for the core, the screen comprises a copper foil wrapped with an aluminised plastic enclosed in a black plastic sheath.
 +
 +The right side picture shows the cable manufacturer and codes, as well as showing the position of the dielectric discs supporting the core.
 ===== Distribution ===== ===== Distribution =====
  
-Example DLA cabinet, this appears completely abandoned, the door is missing, the mains electricity is severed and the input and output coax cables have been cut and removed. These were all grey versions of the BT green fibreglass cabinet used sometimes for the phone distribution PCPs:- \\+Example DLA (Distribution Launch Amplifier) ​cabinet, this appears completely abandoned, the door is missing, the mains electricity is severed and the input and output coax cables have been cut and removed. These were all housed in grey versions of the BT green fibreglass cabinet used sometimes for the phone distribution PCPs:- \\
 {{:​rb:​20151006_175303.jpg?​200|Distribution Launch Amplifier}} {{:​rb:​20151006_175303.jpg?​200|Distribution Launch Amplifier}}
  
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 ===== Consumer Distribution ===== ===== Consumer Distribution =====
 +
 +==== External ====
  
 The Line extender amplifiers and underground splitters fed customer premises either overhead or underground. This was determined by how the BT phone line was cabled. ​ The Line extender amplifiers and underground splitters fed customer premises either overhead or underground. This was determined by how the BT phone line was cabled. ​
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 Underground distribution was used where there were no telegraph poles allowed such as in new estates. In this case the directional couplers to feed consumers were mounted in BT's footway boxes. Some of these were always prone to run off rain flooding them, so sometimes waterproofing would fail and cause problems. Underground distribution was used where there were no telegraph poles allowed such as in new estates. In this case the directional couplers to feed consumers were mounted in BT's footway boxes. Some of these were always prone to run off rain flooding them, so sometimes waterproofing would fail and cause problems.
  
-The coax was passed through an isolator in the house which also served to allow a changeover from outdoor grade, UV resistant cable to indoor grade cable which was a low smoke and fume cable in case of fire. 
  
-Also, the indoor ​cable could be split to separate out VHF FM radio signal ​from the VHF TV signal feeding the set top box. There was also "UHF bypass"​ adapter which could sit under the STB and upconverted ​the "Must Carries" ​(BBC and ITV/C4) from the VHF distribution band to the UHF band used in a TV.+==== Indoor ==== 
 + 
 +The coax feed from outside was passed to an amplified splitter in the house which also served to allow a changeover from outdoor grade, UV resistant ​cable to indoor grade cable which was low smoke and fume cable in case of fire. 
 + 
 +The each output ​from the splitter would connect to FM / CATV demux, ​the F socket going to the Set Top Box and the "TV" ​style Belling Lee going to an FM radio. These are shown below with the covers on and off. The blue knob is to adjust ​the gain fed to the STB. On the right hand picture, the connector ​in the centre is the dropwire input, it feeds in to an AC/DC blocking isolator so any internal faults in the premises could not result in mains electricity being fed back in to the network. 
 + 
 + 
 +{{:​rb:​20180526_183224.jpg?​200|}} 
 +{{:​rb:​20180526_183725.jpg?​200|}} 
 +{{:​rb:​20180526_183817.jpg?​200|}} 
 + 
 +The Set Top Boxes were Jerrold 450 made by General Instrument. These had VHF output and were fitted with a VHF to UHF upconverter.
  
 +There was also a "UHF bypass"​ adapter which could sit under the STB and upconverted the "Must Carries"​ (BBC and ITV/C4) from the VHF distribution band to the UHF band used in a TV.\\
  
 +{{rb:​jerrold450.jpg?​200|}}
  

rb/coventrycable.1525424624.txt.gz · Last modified: 04/05/2018 09:03 by andrew