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== Background ==
The Distribution Network was for the first 37 years of YSTV's history the only way to watch our [[YSTV Productions|programmes]] before the availability of content via [[Watch Online|our website]]. It mirrors the [[Contribution Network]] used to get video from around campus back to YSTV's studios for broadcasting [[Events Coverage|major events]] around campus.
The Distribution Network was for the first 37 years of YSTV's history the only way to watch our [[YSTV Productions|programmes]] before the availability of content via [[Watch Online|our website]]. It mirrors the [[Contribution Network]] used to get video from around campus back to YSTV's studios for broadcasting [[Events Coverage|major events]] around campus.


== Original Network ==
The [[Original Broadcast Network|original network]] was installed as the university was being built in the 60's.


Whilst the University was being built during the late 60s and early 70s, the decision was taken that a closed-circuit television broadcast system would be a good idea. After an early experiment with VHF distribution and a daisy-chain contribution system that formed a giant ring, the contract was given to the Rediffusion company, whose main business was in distributing paid TV and radio services to householders over wired networks.
== Early 90's system ageing ==
The passing of time had taken its toll on the system. By 1994, various colleges/buildings had been remodelled, leading to removal of the AV racks or cutting of contribution/distribution cables. At the time YSTV moved into [[G/046]], the contribution cable from Goodricke back to the Language Teaching Centre (aka LTC) had suffered a break due to the same building work that had lead to the society's eviction from [[P/X/002]]. This lead to the contribution point in [[P/X/002]] being pressed back into service. Cables were trailed over the roof of Goodricke college from the new studio to the physics building. From here it fed back to the AV rack in [[P/S/016]] before being sent on to LTC.  


A closed circuit system of Audio Visual (AV) distribution and contribution was installed, along the lines of a small urban area commercial system, but with a greater provision for sending video back from the various parts of the university to be broadcast. The system allowed up to 4 channels to be conveyed around campus on a multipair pair cable, with each channel dedicated to a separate pair. Further pairs in the cable allowed for up to 9 channels, 5 of them video and the other four audio-only. Video channels carried both the audio and video signals on a single pair.
At this time YSTV could be seen in Derwent, Langwith, Alcuin, Central hall, Vanbrugh and Goodricke (due to the proximity of the Goodricke snack bar and JCR to [[G/046]] these were fed at baseband into a standard SCART television). Wentworth distribution had been lost sometime between 1993-94.  
An equipment room LTC (adjacent to Central Hall) acted as the transmission hub. For transmission, the video was modulated onto a carrier at 4.5MHz (405-line B+W channels) or 10.7MHz (625-line colour-capable channels) and the audio (at baseband) amplified. Audio-only channels were fed via power amplifiers so that outlets could use passive loudspeakers without further amplification, on the same basis as 100V-line PA systems.
The transmission equipment and televisions were supplied by {{unsure|Rediffusion Vision}}. This method of cable based AV distribution was used in a number of towns in the UK, however it had reached the end of it's technological lifetime by the end of the 1980's. The system installed at the University of York was originally black and white (with a mixture of 405-line (BBC1) and 625-line (BBC2) channels and was upgraded to support colour in the 1980s.
<gallery>
Image:19951213_LTC_rediffusion-racks.jpg|Rediffusion racks in LTC
Image:19951213_LTC_distrubution-cables.jpg|Cable entry and exit in LTC
Image:19951213_LTC_distrubution-modulators.jpg|Video modulators in LTC
</gallery>
Installed alongside the distribution network was an AV contribution network. Located somewhere within most colleges was an AV rack. This was fed from a collection of contribution points located in seminar or lecture rooms in the college using coax for video and twisted pair for audio. Within the rack, the video could be patched in to a video line driver transmitter which was linked via twisted pair to a corresponding receiver over in LTC. The audio was directly patched as this was already balanced line. Wentworth was the last of the original 6 colleges to be built and no system of AV contribution was installed, presumably as a cost saving measure. Langwith and Derwent had been built before the Rediffusion system was commissioned, so although a distribution network was installed, and possibly a link from the old ring system to the new one, no Rediffusion contribution system was installed.


The contribution/distribution system was quite advanced in it's day since it would have been possible to do point to multi-point lectures and video conference across campus. However, it is not known if it every was ever utilised beyond retransmission of BBC1/BBC2/ITV and contribution/distribution of YSTV.
Failed televisions were repaired by using parts from any spares that could cannibalised from the spares from the garage in Wentworth, as the were no longer in production. Despite best efforts, picture quality was suffering, colour would turn to black and white and then back or various interference patterns could be seen on the screen.


The passing of the years had taken its toll on the system. By 1994, various colleges/buildings had been remodelled, leading to removal of the AV racks or cutting of contribution/distribution cables. At the time YSTV moved into [[G/046]], the contribution cable from Goodricke back to LTC had suffered a break. This lead to the contribution point in [[P/X/002]] being pressed back into service. From here it fed back to the AV rack in [[P/S/016]] before being sent to LTC. At the time, YSTV could be seen in Derwent, Langwith, Alcuin, Vanbrugh and Goodricke. Wentworth distribution had been lost sometime between 1993-94. The distribution system suffered from having to use televisions that could receive the Rediffusion signal. This made replacing them difficult, since Rediffusion had pretty much dissapeared and the transmission system was technologically obsolete. The proximity of the Goodricke snack bar to [[G/046]], allowed audio and video to be fed at baseband to a normal television via a SCART socket. The remaining televisions soldiered on, and when required were repaired by using parts from any spares that could cannibalised from the spares from the garage in Wentworth. Despite best efforts, picture quality was suffering, colour would turn to black and white and then back or various interference patterns could be seen on the screen.
An attempt was made to convince the University to invest in installing a new system of coaxial cable (for unbalanced base-band video) and balanced audio around the campus, but the carrot of allowing them to use it during the conference season was unappealing, and nothing happened.


== Vanbrugh Upgrade ==
During the summer holidays of 1995, [[Owain Davies]] visited the station and stumbled across a flyer for video balanced line driver and receiver chips which looked ideally suited as it could send pictures over low cost twisted pair cable, bringing the possibility of a YSTV funded replacement network into reach. [[Vanbrugh Upgrade|Vanbrugh college]] was used to test out the devices.


During the summer holidays of 1995, [[Owain Davies]] visited the station and stumbled across a flyer from Maxim highlighting their MAX435/MAX436 video balanced line drivers and receivers.  
== Two kilometres of twisted pair ==
A budget surplus in 1997 left enough money in the society bank account at the end of year to buy a new set of identical ex-rental stereo televisions and two kilometres of cable - enough to rewire all colleges on campus.


At this point, he did not know if he was return to York or not, however he took the flyer away to read at home. He had come across the benefits of balanced line audio ealier on in his Electronics degree and seen it in practice at YSTV where it was used to convey microphone signals down incredibly long pieces of dirty EM infiltrated cable and be amplified at the other end, resulting in crystal clear clarity. The example circuit diagram seemed a remarkable simple solution, just one ic for transmitter and one for the receiver. He returned to York in September of 1995, however he was not due to start his tenancy on a house in Osbaldwick for a week or so and therefore had temporary accommodation in Fairfax House. It was here that the prototype transmitter and receiver were constructed. Trials of the units were performed in the studio of [[G/046]] using twisted pair audio cable. This soon ran out with the units managing to successfully convey the signal, so he resorted any scrap of telephone cable, mains cable, or any cable he could lay his hands on. The signal did eventually deteriate, usually with the picture going black and white due to a dissapearing colour burst (in fact he was amazed by how much the colour burst could reduce in amplitude and colour in the picture remain). He experimented with different resistor and capacitor networks on the feedback loop of the receiver amplifier in an attempt to equalise the high frequency loss of the cable. It was demonstrated to various members of the station using two monitors, one showing before transmission and the other reception with a sea of cable of the floor. The subject under test was given the challenge to determine which monitor was showing the picture that had gone down the various different types of cable. At this point it was decided to inform AV of the idea, since they were the other stakeholder in the network. A meeting was held and they seemed quite interested in the idea and they offered to {{unsure|loan}} the electrical fix installation plans for the University. Their collection was quite comprehensive covering most of the University's buildings, from the colleges down to the VC's bungalow. On these plans were marked the locations of the various contribution points, AV racks and routing information of the cables linking the two.  
During the summer holidays of 1998 newly appointed Network Engineer [[Rob Sprowson]] convinced YSTV that it was time to replace the Rediffusion network, to install an entirely [[New Broadcast Network|new network]].


Owain had found in LTC the composite output from the contribution feed from Physics. The picture was in good condition, meaning the interference problems were occuring on the distribution side of the network only. Armed with the knowledge from the plans, LTC began to make more sense. Three things came out from this visit
Despite the availability of content online it remains a valuable means of raising the society's profile on campus and generating interest in our output, the [[Current Broadcast Network|status now]] is basically the 1998 layout minus sections lost to new building works, with some new links installed and a few of the TVs relocated.


* LTC could act as the distribution for the new network since the composite was good.
== IP-Based Distribution ==
* Since the composite was good, a lot of the wiring must be good and therefore could be reused.
As time went on, and the network slowly degraded, repairs became difficult, and in many cases impossible because most of the routes the cables take have been declared off limits due to asbestos. As a result of this, [[Simon Harris]], the network engineer who didn't have much of a network to be engineer of, proposed making use of the actively maintained campus data network.
Seeing as we already had a webstream by this point, it was a simple task to set up a second, higher quality stream specifically for on-campus use by these laptops. The name of the laptops? [[Drains]] which, as Simon will explain, is because they are at the end of a stream. As of September 2009, the system has already been used to get YSTV's content to The Courtyard, YUSU's own bar.
Drains are now mainly comprised of just Windows XP, running Google Chrome fullscreen.


Audio driver used SSM2142/SSM2141.
[[Category:Tech Team History]]
 
== Beyond Vanbrugh ==

Latest revision as of 12:20, 24 July 2021

Background

The Distribution Network was for the first 37 years of YSTV's history the only way to watch our programmes before the availability of content via our website. It mirrors the Contribution Network used to get video from around campus back to YSTV's studios for broadcasting major events around campus.

The original network was installed as the university was being built in the 60's.

Early 90's system ageing

The passing of time had taken its toll on the system. By 1994, various colleges/buildings had been remodelled, leading to removal of the AV racks or cutting of contribution/distribution cables. At the time YSTV moved into G/046, the contribution cable from Goodricke back to the Language Teaching Centre (aka LTC) had suffered a break due to the same building work that had lead to the society's eviction from P/X/002. This lead to the contribution point in P/X/002 being pressed back into service. Cables were trailed over the roof of Goodricke college from the new studio to the physics building. From here it fed back to the AV rack in P/S/016 before being sent on to LTC.

At this time YSTV could be seen in Derwent, Langwith, Alcuin, Central hall, Vanbrugh and Goodricke (due to the proximity of the Goodricke snack bar and JCR to G/046 these were fed at baseband into a standard SCART television). Wentworth distribution had been lost sometime between 1993-94.

Failed televisions were repaired by using parts from any spares that could cannibalised from the spares from the garage in Wentworth, as the were no longer in production. Despite best efforts, picture quality was suffering, colour would turn to black and white and then back or various interference patterns could be seen on the screen.

An attempt was made to convince the University to invest in installing a new system of coaxial cable (for unbalanced base-band video) and balanced audio around the campus, but the carrot of allowing them to use it during the conference season was unappealing, and nothing happened.

During the summer holidays of 1995, Owain Davies visited the station and stumbled across a flyer for video balanced line driver and receiver chips which looked ideally suited as it could send pictures over low cost twisted pair cable, bringing the possibility of a YSTV funded replacement network into reach. Vanbrugh college was used to test out the devices.

Two kilometres of twisted pair

A budget surplus in 1997 left enough money in the society bank account at the end of year to buy a new set of identical ex-rental stereo televisions and two kilometres of cable - enough to rewire all colleges on campus.

During the summer holidays of 1998 newly appointed Network Engineer Rob Sprowson convinced YSTV that it was time to replace the Rediffusion network, to install an entirely new network.

Despite the availability of content online it remains a valuable means of raising the society's profile on campus and generating interest in our output, the status now is basically the 1998 layout minus sections lost to new building works, with some new links installed and a few of the TVs relocated.

IP-Based Distribution

As time went on, and the network slowly degraded, repairs became difficult, and in many cases impossible because most of the routes the cables take have been declared off limits due to asbestos. As a result of this, Simon Harris, the network engineer who didn't have much of a network to be engineer of, proposed making use of the actively maintained campus data network. Seeing as we already had a webstream by this point, it was a simple task to set up a second, higher quality stream specifically for on-campus use by these laptops. The name of the laptops? Drains which, as Simon will explain, is because they are at the end of a stream. As of September 2009, the system has already been used to get YSTV's content to The Courtyard, YUSU's own bar. Drains are now mainly comprised of just Windows XP, running Google Chrome fullscreen.

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