As a recent graduate, Andrew Burnett joined the Colour Television Design Department at Marconi in Chelmsford in 1968. In his talk "Designing for Colour TV 1968-1973" at the Museum of Communication on 23rd September 2015 he described his role in the team that designed the Marconi Mark VIII Broadcast TV Camera and a Transmitter Logic Control Unit.   


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The Marconi Mark VIII Broadcast Colour Camera, fitted with an Angenieux 12x Zoom Lens

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Andrew described how the camera was actually in two parts: the camera head containing the Plumbicon pick-up tubes, controlled by the camera operator who concentrated on framing and focussing the image on the viewfinder, and the Camera Control Unit, controlled by an engineer who was responsible for the technical quality of the image.

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Inside the Camera Head the light entering via the lens is divided into its Red, Green and Blue components by dichroic filters / prisms and picked-up separately by three Plumbicon camera tubes. The RGB signals then travel by cable to the Camera Control Unit.

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The Camera Tubes and the Cathode Ray Tube have very non-linear characteristics. The (analogue) interface circuitry had to ensure that the final display on the CRT was a linear representation of the original scene. Andrew's work was concerned with the gamma (contrast) corrector and related circuitry.

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Examples of changes in scene reproduction which have to be corrected to provide the final display on the CRT.

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The big advance in the Marconi Mark VIII camera was the provision of Automatic Set-Up of the many parameters. This reduced the number of staff required to set up the camera, which was not necessarily acceptable in all quarters!

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The result of the design team's work was the very successful Marconi Mark VIII Camera.

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Andrew's next project concerned the switch-on procedure for back-up Television Transmitters in the event of failure of the Main Transmitter.

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The output device for a high-power TV transmitter in those days was a very large Klystron tube "about the size of a dust-bin" according to Andrew. The snag was that after switching on the Heater supply it required 15 minutes to reach operating temperature when the HT supply could be switched on. This was a problem in designing a back-up transmitter required immediately upon failure of the main transmitter. 

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This was the (analogue) Transmitter Logic Control Unit that Andrew designed for this application.  

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After Andrew's most interesting presentation he was thanked by LRS Treasurer Peter Dick GM4DTH and presented with an honorarium. 

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The attendees then adjourned to the MoC exhibition area to see the 2015 exhibition "From Flanders Fields to Flying Bombs". There was also a TV camera demonstration set-up. 

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The Lothians Radio Society is most grateful to Prof. Tom Stevenson, Winnie Stevenson, Dorothy Brankin and their colleagues at the Museum of Communication for hosting this meeting and providing refreshments.

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