WHY the sets and aerials need to be altered 

20 August 2018 tbs.pm/65691

A FAMOUS SCIENTIST EXPLAINS

 

From the TVTimes for 22 September to 1 October 1955

MYSTERIOUS new words are now entering non-scientific homes — “Band I,” “Band III,” “Channels” and other oddities. They used to be the exclusive property of technicians, but now there is an independent television programme they come to perplex the general public.

You still do not have to worry. With an installation of the right kind, you will get your choice of programmes without needing any more technical skill than the ability to turn a knob.

But that phrase “an installation of the right kind” is important. Your radio dealer will see that you get it, but you will have to pay for it — and you will probably want to know why it is necessary and what it is all about.

Like lightning

THE signals which make it possible for moving pictures and sound to reach us from studios and transmitters tens, and even hundreds, of miles away travel like waves.

They travel, like lightning, at a speed which would take them about seven times round the earth in a second and they can follow each other in very quick succession.

Which is fortunate, because it takes thousands of different signals every second to build up a picture on your screen.

As long as the waves from each transmitter are of different lengths they will not, so to speak, collide with one another. Your receiver can thus pick out one particular lot, ignoring all the signals of a different wavelength.

It’s all agreed

Professor A. M. Low, a TV expert, makes this technical matter easy to understand

Obviously, if more than one station sent out signals on the same wavelength, there would be a mix-up. The pictures on your television screen would look like a drunken man playing with a kaleidoscope and the sound even odder than some modern symphonies.

So we have agreements, both nationally and internationally, that certain wavelengths are reserved for certain stations and no one is allowed to talk out of turn or “poach” someone else’s wavelength.

You can compare the arrangement to a racing track which has been divided into lanes. All the runners are side by side, but so long as each stays in his lane, they do not interfere with one another.

Elbow room

BUT just as in racing some runners swing their elbows more than others, and thus need more room, so in radio some kinds of signals need more room or a wider “channel” than others.

Television signals need a good deal of elbow room and so it is possible to have only a limited number of lanes or channels in each waveband or “track.”

Britain can claim only a limited number of wavebands and obviously not all those can be given to broadcast entertainment. In the bands which are suitable for television transmissions, room has to be found for many different services.

The police, fire services, taxicabs, press and air services all have to be given space so that they can transmit and receive without interference.

It would never do for the pilot of an aircraft being guided to an airfield to get a call for a radio-taxi or find splashes from the picture of a beautiful blonde appearing on his instrument panel!

When the BBC started its television service it was given a track called Band I, with five lanes or “channels” in it.

Finding space

UNTIL the expansion of the television network began with Sutton Coldfield in 1949, only one channel was required. Now with transmitters all over the country the BBC uses all the five channels to ensure that the signals from the different transmitters do not interfere with one another.

When it was decided to set up an alternative television service, the question arose where space could be found for it in the already crowded “air.”

Compared with the signals used for ordinary sound broadcasting, those we need for television are very short and of much higher frequency.

Inches count

THEY are sprinters rather than marathon runners, like the signals of 1,500 yards and upwards which enable us to receive broadcasts from two or three thousand miles away.

The short television signals do not generally travel very much farther than the eye can see and from the top of a television mast that is about 40 miles.

These short waves are comparatively easily obstructed and reflected, so that it is doubly important to have the right aerial to receive them.

And when we get down to the yard and two-yard long waves which are used for television, differences of inches in the length of the aerial make a tremendous difference to reception.

All the aerials which have been put up for television so far have been designed to receive signals in Band I. To receive well on Band III with the Independent Television service means an aerial of rather different length.

But it can go up beside the Band I aerial and it has the advantage that it will receive any programmes on channels in Band III which may come in the future.

It looks as if the television aerials which have become a familiar part of the English landscape in the last few years are going to be doubled in number so that everyone can receive the new star-studded independent programmes.

This makes it clear why, and what, you must do if you want a choice of television programmes. The short range of television waves means that wherever you live and whatever set you have, you will — for the moment — have a choice of just two programmes.

There will be the BBC transmissions on the different channels in Band I and the Independent transmissions on the channels in Band III.

Your Band I aerial will not, as a rule, pick up Band III television signals — and vice-versa.

Your set, if it is an old one, will need adjustments so that you have the choice of your local channel in Band I or in Band III.

New sets are made so that they can be set to receive a channel in Band I or a channel in Band III as you wish.

But they will not give you a choice of any of all the channels in use, as your sound receiver gives you a choice of dozens of stations.

Fixed up

THERE would, in any case, be no point in it because there will be only two programmes at first, even though they may go out on half-a-dozen different channels.

Perhaps it has all been rather confusing in the last two or three years with so many different plans and proposals, but arrangements are now complete. If you have your set adapted, or get a new one so that it will give you a choice of channels in two different bands, and if you have your aerial arranged to receive these two different bands, you will be fixed up for years to come, no matter what new stations come on the “air,” with a choice of television programmes.


Archibald Montgomery Low (1888-1956), who was not actually a professor at all, was an inventor whose creations included a whistling egg-boiler, a forced-induction engine, a machine that could convert printed text into Braille, a Fultograph-style fax machine and the cap-detonating sparkplug. He also wrote science fiction novels.

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