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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)

The Buzz Factories

Local radio was no new thing to the BBC - when broadcasting started in this country; all radio was effectively local since there were no networking facilities in position. However, latter-day local radio broadcasting commenced with the opening of Radio Leicester, on a fairly low power as an FM service. This pilot scheme proving successful, further low power stations were set up, and eventually the focus moved on to the 'big cities' - London, Birmingham, Manchester and others. These areas would need rather more powerful installations to cover the required area, but eventually money and (rather grudging) Government approval was obtained for them.

There was a story then current that at one point the Government got cold feet about the project, and was wobbling about withdrawing permission. In order to bypass this possibility, the BBC decided on a fait accompli - get them in and working before the Govt changed its mind. To this end, a number of transmitters were actually flown in by airfreight from the USA , since no British manufacturers could provide the goods off-the-shelf. The stratagem worked, though the installations were rudimentary indeed.

Sutton was to be host to two of these new sites - 'Radio Birmingham' as it was then called (it later became Radio WM when the West Midlands conurbation came into being) and 'Radio Derby'. The entire operation was conducted on a shoestring, and had to be done from existing sites. Sutton was fine for Radio Birmingham, but much too far from Derby to give a really good service there. Derby itself is in a river valley and shielded from Sutton, and field strengths, particularly in the city centre where the studios were located, were low. Listeners here were troubled with all sorts of interference, and Sutton became known jocularly by the station announcers as 'the buzz factory'. In later years a small ten-watt relay was installed at the studios themselves, purely to cover the city centre. This situation persisted until the late 'nineties, when a new site for Radio Derby FM became available at Drum Hill, just to the north of the city.

The new transmitters supplied were Gates 1kW units, a variant of the FM-1 series that used an all solid-state driver feeding a single tetrode amplifier valve. They were in the typical American style - over there, local radio transmitters are just a box that you bung into a corner of the studio control room, and then forget. They were made as simple to operate as possible - indeed, they had few operational controls, 'Plate On' and 'Plate Off' pushbuttons and a paddle switch labelled 'Raise' and 'Lower' (this operated the output coupling loop so as to alter the output power. The valve was driven in such a manner that it was almost impossible to damage by mistuning). Maintenance and troubleshooting was intended to be done by an outside firm of contracting specialists, not studio staff. This being the case, no access to the innards was encouraged, and the back door of the unit was firmly screwed shut. This didn't suit BBC methods, so an immediate modification was to remove the screws and install a rear-door Castell key locking system, interlocked to the mains supply isolator. A small earthing wand was also provided.

Aerial installations were quite simple. From memory, Radio Birmingham had four tiers of two sets of yagis per level, horizontally polarised and pointing west and south, covering Birmingham to Wolverhampton . The radio Derby setup was even simpler: two tiers of one yagi per level, pointing rather east of north and covering Derby and Burton-on-Trent . (Burton was not actually within the editorial area, being in Staffordshire, but there was no way of avoiding covering it, so its citizens were treated as honorary Derby residents and included in news broadcasts. When the site move to Drum Hill was made, coverage in Burton suffered and there were complaints). Interestingly, the Derby aerials were mounted with their elements at 45 degrees to the horizontal, thus producing one of the first mixed-polarisation stations, though in those days they called it 'slant' polarisation.

n use, the transmitters were very reliable, although in the early days the monitoring was extremely sketchy. It consisted in fact of a set of lamps on the control desk, basically indicating whether programme input (landline from the studios) and RF output (from the transmitter) were normal. Monitoring the output had to be done on a Hacker portable radio (Hacker in those days meant a respected set maker, not a dodgy prime minister nor an antisocial web user).

Eventually a set of spares for the equipment arrived. I was particularly bemused by one item, a spare inductor. The packet contained a straight length of copper wire, plus a slip of paper saying 'wind this round the shank of a quarter-inch twist drill to make a coil of ten turns, one inch long'. I wonder how much it cost to fly that across the Atlantic . Local radio was a little unusual in opening on FM only. Listeners on that band in those days were not great in number, and the studios were continually complaining that what they needed was a medium-wave outlet. Eventually, they were given one, though again it was all done at minimum cost. In the case of Radio Birmingham, there was a lash-up consisting of a Marconi 5kW AM transmitter installed in a corridor (the 'Zoo') which initially fed a sloping-wire aerial supported from the main mast. This wire passed directly over the main transmitter block, and was a deep embarrassment from the start. The field strength inside the building was enormous, and Radio Birmingham found its way into most of the programme distribution amplifiers, being both heard and seen.

To overcome this, another arrangement was speedily devised; the wire aerial was removed and the transmitter now fed a couple of 150ft. pole radiators down in one of the fields. The mast base pads were made from railway sleepers, and the ATH's (Aerial Tuning Huts) from tiny fibreglass shelters of the kind then used by road works night watchmen. The poles were driven with a suitable combination of power and phase so as to produce a main lobe pointing at Birmingham , and two deep nulls centred on London and Manchester, which were using the same frequency. Cunningly, the masts were sited in such a position that the London null also coincided with the main television mast. This was done so that the TV mast would not reflect or re-radiate any of the signal, and so spoil the radiation pattern. Unfortunately, the signal could not be kept off the mast stays, and these re-radiated with abandon. This upset the performance of the installation somewhat. Field strengths inside the building were now lower, but still high enough to make faultfinding using sensitive measuring gear a misery . Eventually another site became available when Independent Local Radio started up from Langley Mill, and to everyone's relief this was used instead and the temporary setup at Sutton was torn down.

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