A Solid Step Forward 

12 March 2018 tbs.pm/65193

From ITV75, published in December 1974 by the Independent Broadcasting Authority

A new uhf transmitter brought on air every week… some 50 a year in 1975, 1976, 1977, 1978 and 1979. This intensive constructional programme will bring the total of uhf transmitting stations to over 400. Some 150 are now in operation, enabling 19 out of every 20 people in the UK to receive 625-line colour or black-and-white pictures.

But the days when a new transmitter would bring 625 lines for the first time to several million people have gone. Only The Wrekin transmitter in 1975 will add some hundreds of thousands. Most of the stations now being built are for under 10,000 people – some only just over 1,000. The big commanding stations with tall masts and high powers are mostly built and working. But, unfortunately, such is the nature of uhf television that there are still many hilly areas where it is difficult if not impossible to receive uhf television.

And wherever one of those ‘gaps’ has more than 1,000 people not receiving the existing stations then you can be sure that the site planners working on the joint iba-bbc programme will have tentatively identified it and marked down the need for a local relay. Unfortunately it is one thing to identify a requirement, another matter to bring the necessary relay on the air.

Power supply and drive unit for a high-power uhf transmitter with the drive unit withdrawn for servicing. Normally the transmitters are run unattended.

Transmitter buildings for a high-power unattended UHF transmitter.

Often the need for a relay is well defined; occasionally one cannot be certain until other nearby stations are transmitting. It’s a question of surveys, computer studies, a patient search for suitable sites where a transmitting aerial would put the signal where it is needed without causing interference to other stations.

The UHF transmitting aerials are normally enclosed in a large cantilever section at the top of the mast.

Often an ideal site does not exist, or if one is found it may not be available or may be subject to lengthy inquiries and negotiations. Local people may not want a transmitting tower at the bottom of their gardens, or may feel it would be an eyesore on the nearby hill. In practice television engineers have developed designs that are as unobtrusive as possible and often avoid the ridge of a hill. But still sometimes it is a matter of carefully weighing questions of environment against the need for a good TV service. And sometimes a TV mast – such as the iba’s unique concrete tower at Emley Moor – actually proves to be a tourist attraction!

But it does take time; and these days nobody sees why they should not have good TV at the turn of a switch. Anything that can be done, once all the necessary permissions have been obtained, to speed up the building of a station is welcome news to public and broadcasters alike.

And one very important step forward was taken by the iba engineers during 1974. For the year saw the first use of a new range of all-solid-state transmitters and a novel form of pre-fabricated steel container units to replace conventional buildings.

‘All-solid-state’, some readers may be saying, ‘that means transistors instead of valves doesn’t it? And surely valves went out years ago in favour of transistors?’

Well, yes and no. Certainly for all iba uhf transmitters the number of ‘valves’ has been very small indeed. But they have always been needed in the final amplifier stages. Nobody has yet been able to develop, for example, the 80,000 watts of TV power needed at the Crystal Palace or even the 1,000 watts used at some local relay stations from transistors.

But real progress is being made and it is now possible to have ‘all-solid-state’ transmitters of 10 watts output (and soon possibly 50 or even 100 watts). This may not seem much power, but it is just what is needed for the small gap-filling stations that cover a radius of perhaps two, three or four miles.

And by going solid-state with carefully designed transmitters, many advantages are possible both for viewers and the broadcasters. Reliability and consistent performance over long periods; stations that can be confidently left unattended, not just for days or weeks but for months. Maybe the flying squad of mobile maintenance engineers will drop in just once or twice a year, after, that is, any ‘teething troubles’ have been eliminated.

And when a fault does occur the design is such that the team will not have to carry out any highly-skilled work on the spot, but just have to pull out and replace a complete subunit which can then be repaired without undue urgency at the base workshops. The whole of the transmitting equipment has been designed so that no longer will it be necessary for these teams to take along elaborate test equipment.

But that is not all. The use of the special ‘container’ building means that it becomes possible for much of the station to be built into the container at iba’s central stores and workshops in north-west London, and then taken on a specially-built vehicle to its final destination, which may be a remote hill in Wales or whenever gap-filling is needed. The vehicle is designed so that the container can be slid off gently on to a prepared site within the base of the aerial tower or immediately alongside. No special cranes or other unloading equipment are needed, and the final connecting up of the station takes just a few days.

The first of these container stations, equipped with all-solid-state transmitters, was installed at Morpeth in the summer of 1974, but already many more of these stations are now in operation.

Of course, this does not mean that a new station now takes only a few days. There is still the aerial tower, often 150 ft high, to build; and often the most time-consuming operation is getting permission to use the site.

But it is a step in the right direction. And the new ‘10-s container stations’ as they are known by the iba engineers, have certainly speeded up the opening of stations. And if by chance you switch on your TV receiver at 9.10 am on any Tuesday morning you’ll receive the special iba service to dealers, listing the new transmitters on test or opening shortly. There have been significantly more names in the lists since iba went container solid-state.