ABN 2 TV HISTORY
By Ken Frank (letter received 8/8/2006)
With the pressure of an 'on-air' date set, it seemed with complete disregard to the engineering aspect, we just had to meet the target come hell or high water, I don't recall our ever letting the party down. (Niceties such as timing and correcting for high frequency loss on long video cable runs). Nevertheless Australian Standards/Australian Broadcasting Control Board standards had to be met before being permitted to go to air. Horizontal shift of the picture on switching and some time degradation of picture sharpness was a matter to be attended to later. Timing was important wherever signals were switched to have their syncs matched. To achieve this, delay cables were used preferably in the line/field drives and blanking cables to the equipment. It was necessary to provide some video delays. Pulse cables were UR70 and video UR57. Initially all cable came from the UK, later local manufacture took over, and quality was rather poor, even had discontinuity of the braid and often the inner was knotted! A delay cable room was set up below Master Control, there would be miles of cable there - I forget how much. Tom Daly-Hall designed and fitted rows of cable drums for the delay cables. Eric Hitchen was the expert on equalising the response on vision cables.
Test equipment in the earliest days, the only oscilloscope we had was the Cossor 1035 - dual beam with bandwidth of 2/3 Mc/s and 100Kc/s with much cross-talk between the beams. We flew by the seat of our pants, much guesswork. What pleasure when the first Tektronix 524 arrived - a delightful instrument to be able to readily see one tenth of a microsecond - just wonderful. Using this first 'scope' in the cramped and hot environment of the Arcon, the thermal cut-out kept tripping off. An ABC Technician solved the problem by shorting out the safety device. The inevitable happened - the mains transformer burnt out! Such a mass of windings, no local company would attempt to re-wind it. It took many months before a new transformer could be imported and installed. The Marconi Line Strobe was a very useful instrument, it took a bit to learn how to drive it. The Marconi differential sweep was superb for adjusting the frequency response of camera channels - many found it difficult to use.
We had some problems with the interference from air-conditioning and with lighting - saturable reactors - I don't recall the details (Brown Boveri), a device consisting of a reasonable stack of transformer laminations and having coaxial windings. I don't recollect its use here or maybe elsewhere.The motorised camera crane posed a major problem - it should normally be connected to the electrical earth. This would have required insulated separation. Should by chance a potential build up between the two poor cameraman, they could get an electrical shock. Undesirable in a way but the only option was to also put the motorised crane on to the technical earth. With such an excellent technical earth, electrical hum and interference eliminated, it meant a good clean output signal, it could be said, "OK leaving here"!
However, if we had a microwave link to carry the signal to the transmitter 50 yards away all would have been OK. Multiple coaxial conductors enclosed in a large aluminium sheath, this conveyed the studio signal to the transmitter. This coax carried the standard studio video output of 0.7 volts plus 0.3 volt of syncs. Superimposed on this was up to 11 volts of 50 cycle hum. This was due to the two complexes being supplied by two different sub-stations, and hence the coax sheath carried the earth leakage current between the two substations. A major problem, fortunately Brian Madeley solved the problem by building an isolating amplifier freeing the signal from all earth connections.
Ken Frank's involvement with the Gore Hill installation began in 1957 as
the engineering representative from AWA/Marconi. During his career Ken has been
involved with television broadcast design, contracts and defence electronics.
He retired in 2000.