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THE TRANSMISSION GALLERY

TALES FROM A COLD FIELD

Being fairy-stories told to the author as a young engineer
© Ray Cooper, 2005 (2nd revised edition, Jan 2006)

Hullabaloo and Custard

. were the official names of the kangaroo mascots used by the BBC in its publicity drive to announce the coming of 625 line television on UHF. This was of course the BBC2 channel, in monochrome only, and made necessary the renaming of the old 405-line BBCtv channel to BBC1.

Custard was never much in evidence (like jam, that was for tomorrow) but there was certainly plenty of hullabaloo available to make up for it. The new service opened in London only (of course) from Crystal Palace , when the infamous power-cut incident on the opening night led to all programmes being cancelled. At this time, the new BBC2 installation at Sutton was in the throes of installation.

The new transmitters were 25kW units by Marconi, and used klystrons in the final amplifier. Nothing like this had ever been seen on site before, and caused many head scratchings and prognostications of doom. At the same time, new aerials had to be provided, which involved rebuilding the top of the mast, described elsewhere. All the same, when the December 1964 target date was near it became evident that the new aerials would not be ready on time, so a temporary aerial was provided on the old 150ft reserve mast, providing some sort of a signal to the Birmingham area in time for the opening date.

Despite being 'a cutting-edge product by one of the leading manufacturers in the country', the new transmitters proved to be rather unstable and a bit of a disappointment. Though, to be more accurate, it was the drive (exciter) units that had poor stability - the high-power amplifiers in themselves were pretty good, and suffered from only one shortcoming, which will be dealt with shortly. The drives, however, were a continuous source of trouble. When I use the word 'unstable', this is not to imply that the unit would dive off into violent oscillation in quite the manner of the 405-line vision transmitter: but rather, the linearity of the drive would change quite markedly over the short term.

The staff spent so much time fiddling with these drives in an attempt to maintain transmission of something that looked like a vision signal, that the fact became noticed by the station EiC. This led to the issuing of a memo, and ultimately to the infamous 'Closed-Doors' experiment. Basically, the memo said that too much fiddling about was going on, and accordingly the drives would be lined up 'properly' by the shift SME, after which the transmitter hall doors would be closed, and in fact locked with a padlock and chain, to prevent unauthorised twiddling.

This was done early on a Monday morning, after which the locks were applied and the keys handed to the EiC. No more than ninety minutes later, the key was being asked for, because by this time the pictures had become unusable.

A lot of the early problems were probably due to staff inexperience, coupled with the fact that the line-up procedures given in the handbooks were pure gobbledegook and in fact couldn't be made to work anyway. Over the following months, low cunning on the part of the staff devised line-up procedures that did, in a way, work, and devious strategies were evolved which kept the gear on-air without too much interruption. But to the end of their days, these original drives remained unstable, and it was a rare shift that passed without someone having to go and give them a surreptitious tweak. Eventually after many years the fact that the drives were a total liability was recognised, and they were torn out and replaced with much more modern, and stable, Pye IF Modulation drives, to everyone's immense relief.

And now, in Colour >

 
mb21 by Mike Brown
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