In an ITA transmitting station 

19 July 2018 tbs.pm/66597

 

Programmes come to the ITA’s transmitting station from the studios of the programme company in the form of electrical signals. The work of the transmitter is to magnify these signals and mount them on “carrier waves” which will radiate them from the transmitting mast or tower.

Signals come into the station by underground cable, or by microwave transmissions received by a dish aerial on the mast. The signals generally come into the building’s GPO ROOM, since it is the Post Office which is responsible for the main network of cables and microwave links that connect the studios and transmitters of Independent Television throughout the country.

One of the Authority’s new cylindrical masts, nine feet in diameter and rising nearly a quarter of a mile into the sky. The Winter Hill mast is 1,015 ft. tall and those at Belmont and Emley Moor are 1,265 ft., the tallest in Europe.

Sound and picture components are separate signals. They are sent from the GPO Room to the CONTROL ROOM, where the station’s duty engineer is in charge of instruments to monitor the performance of different parts of the transmitter. He can obtain direct telephone contact with the GPO engineers at certain linking points for the incoming signals, or with the studios of the local programme company. His television sets show the picture as it comes into the station and as it leaves the transmitter.

From the Control Room the sound and picture components of the programme go to the SOUND TRANSMITTER, and to the VISION TRANSMITTER. There are usually two sets of these transmitters, working either together or separately, so that routine maintenance can be carried out without interrupting the programmes and so that in the case of a fault the station can stay on the air.

In the transmitters the signals are amplified in steps from a small fraction of a watt to sometimes as much as 10,000 watts. The signals are then put on to a “carrier wave” which has a fixed frequency corresponding to the tuning of the television receivers which have to pick it up. This carrier wave frequency is controlled by the Crystal Drive Unit. The powerful transmitter amplifiers produce a considerable amount of heat. To keep the temperature down either air or water cooling systems are provided.

When the sound and vision signals emerge from their transmitters, at full power and ready to be broadcast, they are combined in the COMBINING UNIT. The united signal passes to the AERIAL SWITCHING FRAME, where a special kind of switch can route the television signal into the two halves or one half of the transmitting aerial in a number of ways.

To carry the finished signal up to the aerial, two co-axial feeder cables run from the Aerial Switching Frame up the mast or tower. The aerial is carefully tailored to radiate the signal in the pattern required, less power being radiated in the directions where it is not needed—for example towards the sea or in directions where too strong a signal would interfere with the television services of another country—and the greatest power concentrated in the directions where it is most needed.

Power for the transmitters comes to the station’s SWITCH ROOM from the national electricity grid. Automatic voltage stabilizers keep the current at a steady voltage, and a switchboard distributes it around the building. In case of a power failure a second supply from a different area is arranged, where possible, or a stand-by diesel generator is installed.

At all staffed transmitting stations there are also slide scanners and record players that make it possible for announcements and captions to be broadcast from the station itself if an emergency arises. Some stations also have a film scanner.

 

 


 

One last word. However good the signal radiated from the station it is still for the viewer to make his contribution to good reception. The right aerial, properly installed, is essential. The aerials that receive the BBC will not properly serve for Independent Television, because for one thing the frequency is very different. The strength of the signal received will of course depend on a number of other factors, not least the distance from the station. In case of difficulty in getting a good picture the local dealer should be consulted about the aerial.

 

Ninety-seven per cent of the people of the United Kingdom are within range of one or more of the ITA’s 30 transmitting stations. They cover 13 service areas. More transmitters are being built to extend or improve coverage.

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