ALAN CASH - web pages
Collection of books on Welwyn Garden City
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ALAN CASH - web pages Collection of books on Welwyn Garden City |
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* This book was published during WW-II but there is no date anywhere in it. A sentence in the book reads "We've had some pretty bad news to swallow during the last three years". I am guessing it was published in about 1943, or possibly late 1942.
I know that this book is not about Wewlyn Garden City so it really does not belong here. However, it was produced by Murphy Radio in Welwyn Garden City at a time which my uncle worked there so I have included it anyway. He worked there from 1938 to 1945 on War Office Wireless Set No. 14 and No. 28, then later on Beacon Range, and then for the Admiralty on Radar equipment and Mixer units.
The purpose of the booklet was to help ordinary people keep their radio sets going at a time when many radio engineers were in the services or working on war work.
The following passage is from the Introduction:
“A MILLION RADIO SETS IDLE”
This is a very significant statement. It means that two million people at least are cut off from official B.B.C. announcements and from the inspiration and guidance which our leaders give to the people in war time by means of broadcasting.
It is an urgent necessity that something is done to relieve the situation. The tools to put the matter right are service men, components, valves, and time. They are precious tools, and our munitions industry and the Armed Forces have, quite rightly, first call on those tools.
This book is an attempt to ease the situation.
Many thousands of wireless sets could be put right to-morrow by set-owners themselves if they were told a few simple facts about the sets.
We hope this book will tell you the facts. We hope as a result that- many
thousands of receivers will once again burst into life through simple adjustments,
which you may be able to make after reading this book.
Listening in war time is important. This book may be the means of bringing the
B.B.C. news back into thousands of homes without taking up the valuable time
of skilled engineers who are wanted for still more urgent jobs, and without
using up valuable material.
Excerpts from Chapter One - How a Wireless Set Works.
A wireless set is an instrument for reproducing speech and music, not a machine for making music. This is a very important point which is far too often overlooked. Remember that your set cannot improve upon what the broadcasting station sends out; in fact you have got to keep the set in as good order as possible if you want to hear anything like a true reproduction.
In this chapter we tell you how a wireless set works. You will be able to see, with the help of the simple chart at the end of the book, how a programme is converted into wireless waves, how it travels through space, and how it finally reaches your set, where the wireless waves are turned back into sound that you can hear.
With the exception of the few simple but important adjust ments which we will show you how to make, you will see that we do not wish to worry you with a difficult study of the “innards” of your set. Regard the set itself as you would regard a gramophone - a self-contained “box” for reproducing music - and a “box” that you do not have to bother about.
The Broadcasting Station
(1) The announcer speaks (or the orchestra plays) into a microphone. His voice causes the air to vibrate, and this in turn makes a part of the microphone vibrate.
(2) The microphone changes the small “voice vibrations” into feeble electric impulses.
(3) These are the impulses which, after a long and tiring journey through space, must eventually cause part of your loudspeaker to vibrate.
(4) As these little impulses are so feeble, they cannot manage the journey alone and unaided. They would fade away before they had travelled an inch from the broadcasting aerial. So two things are done for them. First, they are strengthened and built up (amplified by valves).
(5) Next, they are provided with a means of transport! Silly as this may sound, it is true! Many valves and enormous power are used in the broadcasting station to manu facture another set of very strong electric vibrations. These vibrations, or waves, are created specially to carry the feeble electric vibrations of the voice on their journey. They are known as the “Carrying” or “Carrier” waves. They have no other use, and once they reach your set they have to be got rid of at once. Sometimes, when the set goes slightly wrong, they are not cleared out of the way—and the result is a whistle! It is really very much like ordering a parcel from a shop in a distant town. The parcel cannot travel by itself, so the assistant puts it in a van. But you don’t want the van in your house! You take the parcel in by the door and forget all about the means of transport.
(6) Anyway, having manufactured the strong “Carrier” waves, and having turned the voice waves into electric vibrations, the two are sent out by the last valve at the broadcast station, one literally riding on the other. Only one more thing is necessary.
(7) The broadcasting station has to send Out its programme on a definite wavelength—so that, when you see Home Service in the newspapers, you know exactly where to find it on the dial of your receiver. So the “carrier” wave and its passenger, the “electric voice vibrations”, are passed through a tuning device which consists of coils and condensers. This device adjusts the measurement—or length—of the waves. The operator at the broadcasting station can alter their length (their wavelength) by turning a knob, just as you can choose different lengths of wave (different wavelengths) by turning the tuning knob on your set.
(8) The waves are now passed to the aerial and earth wires at the broadcasting station, and flung out into space, to your waiting aerial.
(click on the images to enlarge)
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Title page |
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Mains set | |
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Summary of things to do | |
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The insides of 2 sets. [This is what the inside of a radio set looked like when I was a boy. The cylindrical things are thermionic valves - or just valves for short - known as "vacuum tubes" in America. Some time after the War, the valve was replaced by the transistor. Then, after transistors were miniaturised, printed circuits came in. All the fun had then gone from exploring the inside of a radio.] | |
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How radio works |
(click on the images to enlarge)