Vanbrugh Upgrade

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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, though at this point, he did not know if he was return to York or not, but took the flyer away to read at home.

The virtues of balanced line audio earlier were already known at YSTV where it was frequently used to convey low level microphone signals down incredibly long pieces of dirty EM infiltrated cable yet resulting in crystal clear clarity after the amplifier: any noise pickup affects both wires equally, so by subtraction the noise is cancelled.

The example circuit diagram seemed a remarkable simple solution, just one IC for transmitter and one for the receiver. Owain did return for further studies and set about building a trial transmitter/receiver pair.

Trials of the units were performed in the studio of G/046 using twisted pair audio cable which performed well over the limited lengths available, so any remaining scraps of telephone and mains cables around the studio were used as an extention. The signal did eventually deteriorate, usually with the picture going black and white due to a disappearing colour burst, though this could be compensated to a degree at the receiver.

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
loanUnverified or incomplete information
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 Vice Chancellor'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.

Owain had already found in the LTC hub that the composite output from the contribution feed from Physics was in good condition. Therefore the observed interference problems were occurring on the distribution side of the network only.

Clearly

  • LTC could act as the distribution for the new network since the composite was good
  • Since the composite was good, a lot of the wiring must be good and therefore could be reused

The trial units were installed in Vanbrugh college, taking the short hop from LTC to V/045 vent room over the existing Rediffusion cables, a few short links of mains cable to join to a new section of cable running to the vending machines by the porter's lodge. From here the newly recovered composite video was fed via an amplifier into the JCR, snack bar, and mute monitor above the vending machines.