Distribution Network
Original Network
When the University was built during the late 60s and early 70s, a closed circuit system of Audio Visual (AV) distribution was installed. 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. An equipment room LTC (adjacent to Central Hall) acted as the transmission hub. For transmission, the video was modulated up to 4.5Unverified or incomplete information MHz and the audio (at baseband) amplified at to an amplitude of 100VUnverified or incomplete information. The transmission equipment and televisions were supplied by Rediffusion VisionUnverified or incomplete information. 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 and was upgraded to colour in the 1980s.
Rediffusion racks in LTC
Cable entry and exit in LTC
Video modulators in LTC
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.
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.
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 the teles 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 canniballised 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.
Vanbrugh Upgrade
During the summer holidays of 1995, Owain Davies visited the station and stumbled across a flyer from Maxim highlighting their video balanced line drivers and receivers (part number defeats me, I have been on the website but nothing rings bells)Unverified or incomplete information. 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.