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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)

Something in Reserve

It should by now be apparent that the lack of a reserve transmitter was causing severe embarrassment, and the manufacturers were little nearer producing a suitable product. However, help was at hand in the shape of a curious 'Caravan Transmitter' that appeared on site one day. This seems to have been the pilot transmitter that toured the Birmingham area before Sutton opened, giving demonstrations to the trade, and which turned up at some later sites in a temporary capacity whilst their permanent buildings were being erected. (There is a slight possibility that it may have been the same vehicle that was used pre-war as an Outside Broadcast link. This unit was reported to work in the 60 - 70 MHz band, at about 1kW power. It would obviously have been of less use by this time, since Sutton was now occupying its frequency, and by then much superior OB links were available. On the other hand, archive film footage shows this vehicle in use for the experimental first Calais Outside Broadcast in 1950, in which just about every available item of link gear was pressed into service, making this possibility less likely). Even though 1kW is a bit of a comedown after 35kW, it was still a lot better than totally blank screens and probably gave a usable service to Birmingham , though not much further afield. It was evidently regarded as a Godsend by the beleaguered staff.

Despite this, the caravan still had its own contribution to make to the general chaos. It was parked round the back of the building, and coaxial cables connected it to the feeder changeover switches inside. The caravan had its own test load, and it became the custom to leave it connected to this: the reserve transmitters would be tested every day, to keep the valves conditioned and reassure the staff that it would in fact work if called upon.

In the event of a main transmitter failure, the first step would be to see if it would re-power, and then if not somebody would run post-haste to the van to crank up the reserve. The test-load was selected by moving the connector on the end of a flexible co-ax cable from one socket to another, so while the reserve was running up this connector would have to be moved back. The sockets were mounted on a bracket at ceiling height, and the plug had a screwed retaining collar with a very fine thread.

One day there was the customary bang, and bells, and it was soon decided that the reserve would be needed. Two bods, who we will call D and E, (there must have been plenty of staff about that day) nipped round the back, and started doing the necessary. While D was running up the transmitter, E dealt with the connector.

After a short while, D remarked:

"It's ready to power. You got that connector done yet?"

"Erm. yes."

At which point D powered the reserve: no problems. "Right, I'm off to lend a hand with the fault," said D, who then disappeared.

Well, it wasn't too bad a fault, and was fixed in a quarter of an hour or so. At the end of this time the main transmitter was running peaceably into its own test load.

"We'll leave it like that, to soak for a while. We can switch back at the end of the programme. I think we've all earned a cup of tea."

There was no dissent to that view. After the second cup, and by the time the fault had been thoroughly dissected, somebody suddenly remarked,

"I haven't seen E. for a while. It's not like him to miss tea. Anybody know where he is?"

"Last I saw of him was nearly an hour ago, in the 'van. Oh dear, perhaps we'd better."

They all trooped round to the van, to find E. standing on tiptoe in a frozen attitude with his hands clasped round the connector. When he had fitted it, he'd got the fine thread well and truly crossed and could neither do it up, nor undo it. Nor, from where he was standing, could he reach the 'Off' switch. For the previous three-quarters of an hour he had been holding the connector together, to prevent it from arcing.

Well, he was promptly rescued of course, though it took a while before he could lower his arms below shoulder height, and longer still before his fingers would straighten out from their claw-like appearance.

With the presence of a reserve transmitter, no matter how capricious, some of the heat went out of operations at Sutton, and cock-ups of the majesty of the few just described became more infrequent. Pre-reserve, the one priority in the event of a fault was to get some sort of a picture back for the punters - time could not be spared for a close analysis of causes. Post-reserve, the staff could afford to relax a little and gaze critically at the problem through half-closed eyes and a haze of recently lighted cigarette smoke. There was now time for puzzling features of an incident to be investigated, and suitable strategies advanced. The pulse rate of most engineers returned to more reasonable levels.

Eventually a properly engineered reserve installation became available and the whole system became, as a result, fairly usable. This installation was a Marconi 5kW unit, of the type used as main transmitter on medium-power sites such as Rowridge or Pontop Pike (incidentally, a parallel installation of these units was used as the main transmitter at Crystal Palace - this site of course had much more aerial gain than the other high-power sites, so didn't need as much engine power). For use at Sutton, the 5kW vision unit was narrow-banded a little and by this means its output power could be screwed up to about 6.5kW. Similarly, the sound unit was run at 2kW rather than its nominal 1.25kW.

There followed a breathing space, until the introduction of FM broadcasting in the mid to late 'fifties.

The Quieter Years >

 
mb21 by Mike Brown
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