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rb:coventrycable [04/10/2019 09:46]
andrew [Distribution]
rb:coventrycable [30/03/2020 17:24] (current)
andrew [Indoor]
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 {{:​rb:​blackburnhouse-vandalised.png?​200|Vandalised rear of building}} {{:​rb:​blackburnhouse-vandalised.png?​200|Vandalised rear of building}}
  
-Satellite TV receivers & cable tv modulators and Launch Amplifiers.+ 
 +Master Control room - monitoring all the channels being transmitted and some of the playout equipment, the Video Recorders seem to be S-VHS models. In the left hand side of the rack, there is what looks like the station master Sync Pulse Generators with a changeover unit, in the middle rack there is what looks like a timecode generator. As Coventry Cable used to make some local programming,​ there are probably more for studio use than the Cable distribution side.  
 + 
 +{{:​rb:​covcablemcr1.png?​200|}} ​  ​{{:​rb:​covcablemcr2.png?​200|}} 
 + 
 + 
 +Satellite TV receivers & cable tv modulators and Launch Amplifiers. ​ 
 +In the left hand side picture, you can see (in the rhs racks) some of the Jerrold scramblers used to encode the premium channels ( [[http://​theoldcatvequipmentmuseum.org/​140/​142/​1426/​index.html#​JerroldGIDigitalScramblerEncoderModelDSE--1.JPG]] ) 
  
 {{:​rb:​covcable-headend_.png?​200|}} {{:​rb:​covcable-launchamp.png?​200|}} {{:​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 located in BT's district telephone exchanges prior to feeding the subscriber distribution network. These consisted of several amplifiers with one input and one output boosting the signal. The amplifiers were manufactured by Texscan in the USA, and were 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)+The Supertrunks radiated out from the Head End to distribution sites located in BT's district telephone exchanges prior to feeding ​the trunk network and then the subscriber distribution network. These consisted of several amplifiers with one input and one output boosting the signal. The amplifiers were manufactured by Texscan in the USA, and were 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)
 The supertrunk amplifiers were located in smaller green BT 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.
  
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 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. 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.+The right side picture shows the cable manufacturer and codes, as well as showing the position of the dielectric discs supporting the core (as indicated by the slight abrasions on the surface at regular intervals).
  
 +{{:​rb:​supertrunk.png?​200 |}}The supertrunks followed the routes on main roads, presumably as there were already telephony trunk ducts laid, periodically there looks to have been joints and this diagram shows two amplifiers similar to the ones in the photograph above.
 +
 +GF in the diagram is the abbreviation for the [[https://​telephone-exchange.co.uk/​Coventry-Greyfriars-CMCGF.html|Greyfriars Exchange]] in Coventry.
 ===== Distribution ===== ===== Distribution =====
  
 +
 +{{ rb:​trunk.png?​100|}}The Trunks fed out from the district exchanges to the distribution launch amplifiers, these served an area of a few streets.
 The  DLA (Distribution Launch Amplifier) was made by Texscan in the USA and was locally powered by a Fuba ferro-resonant transformer which also provided phantom power to downstream amplifiers. Mains power was supplied from the utility provider with a consumer unit in the cabinet. The  DLA (Distribution Launch Amplifier) was made by Texscan in the USA and was locally powered by a Fuba ferro-resonant transformer which also provided phantom power to downstream amplifiers. Mains power was supplied from the utility provider with a consumer unit in the cabinet.
    
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 {{:​rb:​dla-cabinet-2.jpg?​200|Green painted cabinet with a differnet design of ferroresonant transformer}} {{:​rb:​dla-cabinet-2-topconnections.jpg?​200|Coax entries on the top}}  {{:​rb:​dla-cabinet-2-cables.jpg?​200|Looking into the duct entries}} {{:​rb:​dla-cabinet-2.jpg?​200|Green painted cabinet with a differnet design of ferroresonant transformer}} {{:​rb:​dla-cabinet-2-topconnections.jpg?​200|Coax entries on the top}}  {{:​rb:​dla-cabinet-2-cables.jpg?​200|Looking into the duct entries}}
 +
 +
 ===== Reverse path and Status Monitoring ===== ===== Reverse path and Status Monitoring =====
  
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 The DLA fed local trunks which were boosted periodically by Line Extender Amplifiers, these were mounted underground in a waterproof sleeve in footway boxes. They were made by ProCATV in Denmark. The DLA fed local trunks which were boosted periodically by Line Extender Amplifiers, these were mounted underground in a waterproof sleeve in footway boxes. They were made by ProCATV in Denmark.
  
-{{rb:​320b_a.jpg?​200|Sleeve, base, amp mounting bracket and locking ring}} {{rb:​320b_b.jpg?​200|Base with mounting plate fitted}} {{rb:​320b_c.jpg?​200|Inside view of mounting plate showing '​F'​ type push in plugs}}+{{rb:​320b_a.jpg?​100|Sleeve, base, amp mounting bracket and locking ring}} {{rb:​320b_b.jpg?​100|Base with mounting plate fitted}} {{rb:​320b_c.jpg?​100|Inside view of mounting plate showing '​F'​ type push in plugs}}
  
 From a THG member:- From a THG member:-
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 reverse amplifier modules. This could be a later version."​ reverse amplifier modules. This could be a later version."​
  
-Some versions had a loop through on the input side and there was a two output version also. This one used a separate RF hybrid for each output leg.+{{rb:​rf-hybrid-module.png?​75 |RF Hybrid module}}Some versions had a loop through on the input side and there was a two output version also. This one used a separate RF hybrid for each output leg. 
 + 
 + 
 + 
  
 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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 Overhead distribution was brought to an 8 way directional coupler mounted at the top of telegraph poles or on the side of buildings (for low rise flats) This fed a twin "​figure of eight" cable with the phone and strength wires in one half and the tv coax in the other half. The unused outlets were capped with a ''​F''​ terminator to both provide a weather seal and prevent ingress / egress of RF.  \\ Overhead distribution was brought to an 8 way directional coupler mounted at the top of telegraph poles or on the side of buildings (for low rise flats) This fed a twin "​figure of eight" cable with the phone and strength wires in one half and the tv coax in the other half. The unused outlets were capped with a ''​F''​ terminator to both provide a weather seal and prevent ingress / egress of RF.  \\
  
-{{:​rb:​tap1.png?​200|}}  {{:​rb:​tap2.png?​200|}}  {{:​rb:​tap3.png?​200|}} {{:​rb:​20180503_134911.jpg?​200|}}+{{:​rb:​tap1.png?​100|}}  {{:​rb:​tap2.png?​100|}}  {{:​rb:​tap3.png?​100|}} {{:​rb:​20180503_134911.jpg?​100|}}
  
 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 prone to run off rain flooding them, sometimes waterproofing would fail and cause problems due to water ingress. In many cases, prompt action to wash the affected unit in clear water and then dry it out with a hairdryer resulted in no lasting damage. 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 prone to run off rain flooding them, sometimes waterproofing would fail and cause problems due to water ingress. In many cases, prompt action to wash the affected unit in clear water and then dry it out with a hairdryer resulted in no lasting damage.
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 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.\\ 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:​bypass-top.jpg?​200|}} ​ {{:​rb:​bybass-base.jpg?​200|}} +{{:​rb:​bypass-top.jpg?​200|}} ​ {{:​rb:​bybass-base.jpg?​200|}} {{:​rb:​bypass-insidebottom.jpg?​200|}}  {{:​rb:​bypass-insidetop.jpg?​200|}}
- +
- +
-{{:​rb:​bypass-insidebottom.jpg?​400|}}  {{:​rb:​bypass-insidetop.jpg?​400|}}+
  

rb/coventrycable.1570182413.txt.gz · Last modified: 04/10/2019 09:46 by andrew