Introduction to Copper Cabling (eBook)

Applications for Telecommunications, Data Communications and Networking

John Crisp (Autor)

eBook Download: PDF

2002 | 1. Auflage
215 Seiten
Elsevier Science (Verlag)
978-0-08-049580-4 (ISBN)

Infos

Because this is a book for engineers the practical coverage is reinforced by use of the latest interanational standards, in particular BICSI standards (USA and international) and EU requirements. This will make the book ideal for the large number of industry-based training courses. Coverage has also been matched to the requirements of the revised City & Guilds 3466-04 course.

*Covers the real-world issues of selection, design, installation, testing, safety, legislation... neglected by university texts
*An easy-to-read introduction that assumes no prior knowledge beyond basic concepts of voltage and current - ideal for non-specialists as well as practitioners
*Covers new BICSI (US / international) regulations and EU framework

Inhalt

Cover 1
Introduction to Copper Cabling 4
Copyright Page 5
Contents 6
Preface 8
Chapter 1. Talking across the Atlantic 9
Chapter 2. Technical bits that may be useful 18
Chapter 3. How cables work 30
Chapter 4. Decibels – they get everywhere but what are they? 42
Chapter 5. How is data transmitted? 54
Chapter 6. We don’t do it like that 67
Chapter 7. Not all cables are the same 72
Chapter 8. Selecting, protecting and connecting cables 85
Chapter 9. Networks 100
Chapter 10. Cables in buildings and between buildings 120
Chapter 11. Does it work? 140
Chapter 12. Staying alive until payday 157
Chapter 13. A brief introduction to fiber optics 176
Chapter 14. Moving on 187
Bibliography 191
Glossary 192
Quiz answers 215
Index 219

Textauszug

1

Talking across the Atlantic

Unless we were to remain happy to communicate by lighting bonfires on hilltops or employing runners or galloping horses, we needed a real breakthrough.

A good idea that wasn’t followed up was the work of the Greek Thales who, in the sixth century BC, was one of the first to investigate electricity and magnetism. He did the trick of rubbing a balloon on his sleeve, and picking up some light pieces of material – actually he rubbed a piece of amber with some fur, but that’s near enough the same.

If he could only have encouraged more people to continue his work, we may have had warp drives and teleporters by now. But no-one showed any interest and, like they say in all good history books, ‘nothing happened for 2300 years’.

In the sixteenth century there was a flurry of interest in devising some form of long-distance communication system. There were many attempts with lights and mirrors, which had limitations where distances were involved. But flashing lights were nowhere as limited as the speaking tube, in which we would shout down a tube with an ear placed at the other end. This would limit the scope for long-distance communications but was resurrected about 200 years later with the idea of banging the outside of the tube with a hammer to send messages in code. This didn’t work either.

Towards the end of the sixteenth century and in the early seventeenth century, we had noticed that the effects of magnetism and many people had great faith in its ability to provide a fast long-distance communication system as well as miracle cures for all ills and almost anything else.

It had been noticed that a compass needle can be deflected by another compass needle and so it was a small step to conclude that if it could be made to happen at any distance then all communication problems are virtually solved. There was a tendency to assume that this small problem would soon be surmounted and we could get on with the real invention bit. Rumors and claims were made for the most unlikely methods.

One very popular method was to make two such needles become ‘sympathetic’ and by moving one, the other would move by the same amount to remain parallel even when separated by enormous distances. Having produced two sympathetic needles, all we have to do is to mark the edge of the compass with the alphabet, and there we are – no-cost instant communications. Despite the small fact that the needles never did align themselves in parallel even when the needles were close together, the rumor spread quickly, probably just because it was such a neat idea that everyone wanted it to be true. A bit like flying saucers and little green men from Mars.

In those days we had to spread rumors from person to person but nowadays we have the media, which are in the fortunate position of not only being able to spread rumors to millions of people at a time but actually get paid for doing so.

When it was accepted that the range was very limited and the needles never did remain parallel, we could still demonstrate that a magnet could be used instead of the first ‘transmitting’ needle and the receiving needle would still be deflected, so the rest of the system could still work. It was soon seen to be limited in range but, and this gave hope, a larger magnet would have a larger range. All we needed to do was to build larger and larger magnets but this idea also died as some calculations were done on the size of the magnet needed for transmission over a few hundred miles. There was also the small problem of interference if more than one communication system was set up in the same area.

The American scientist, Benjamin Franklin was rumored to investigate electricity by flying a kite in a thunderstorm. Now, whether he actually did this or not, it was certainly a good enough story to encourage others to try it and to die in the attempt.

Benjamin certainly did investigate and develop the idea of air terminal or lightning conductors on buildings but even nowadays, many people have the wrong idea of what they are for and how they work. We will look at lightning conductors in a later chapter.

About 50 years later, in Geneva, Switzerland, George Lesage decided to use wire and a pith ball. The point of the pith ball was that it was extremely light and when charged with electricity by a connecting wire they would hold equal polarity of charge and hence repel each other. The pith ball would move away from the wire as in Figure 1.1. If we connect one wire for each letter of the alphabet, all we had to do was to energize the wire corresponding to the first letter and, at the far end, they would watch to see which ball moved. By this laborious process we could spell words, one letter at a time.

Figure 1.1 Really slow telegraphy – but it worked

Electricity is too slow – let’s try something mechanical

Like most methods up to this time, the search was always for a way to generate movement at a distance, usually to point to a letter. This latest version abandoned electricity in favor of mechanical engineering. As usual, it was a good idea on paper but more difficult to actually achieve. This is how it worked, or should have worked. To send a message to your house, all we have to do is to pop down to my cellar, turn a lever until it pointed to the first letter and a system of mechanical gears and drive shafts between our two houses turned the pointer in your cellar. Then on to the next letter. It would probably work if we lived in adjacent houses but there would be rather a lot of friction if we were in different towns. Not to mention the small problems of hills and rivers.

Five years later in 1792 another mechanical solution by Claude and Rene Chappe took a step back towards the ridiculous but within three years of further development they had a winner.

It worked, but the neighbors were not happy

Behind their parent’s house, the two brothers arranged a clock face with just a single hand that swept around the face in 30 seconds. Ten numbers were written on the face so every three seconds the hand pointed to one of the numbers. At the receiving station a few hundred yards away, a similar clock face was set up. The first job was to synchronize the sweeping hand. This was done very simply by striking a casserole dish as the hand passed the vertical position, whereupon the hand on the receiving apparatus was released. A second clang indicated the moment to read the transmitted number.

To the irritation of all in earshot, a series of numbers could be clanged out and hence deciphered by reading the position of the receiving hand. By coding the numbers into letters, a message could be beaten out.

It was soon modified to a system that was purely visible, which must have been an enormous relief to all those within earshot. This was a wooden panel that was painted black on one side and white on the other and the moment that corresponded with the required number was signaled by pivoting the board to change the color.

The day of the big test came in March 1792. With the aid of a telescope, and in only four minutes a message, ‘if you succeed you will soon bask in glory’, was sent over a distance of 10 miles. The message was supplied at the moment of the test to avoid trickery which, as we can imagine, was rife with the demonstration of new signaling methods.

That’s better

The Chappes were happy to see the system work over such distances but synchronizing the clock was a nuisance so they thought of ways to eliminate the timing problem. But was it possible? In 1793, the Chappe Mark III version was unveiled and this was a winner.

The clock was thrown out and instead a semaphore system was built on a tower. The tower had two pivoted arms on it and provided enough combinations to provide a different pattern for each letter and number. A system of ropes was used to reposition the arms as shown in Figure 1.2 and the towers were used to send a message through a series of such towers over 20 miles and to everyone’s amazement, 20 minutes later, a reply was received. Not a bad speed.

Figure 1.2 Chappe telegraph code

Claud Chappe was put on a government salary to build a series of towers over hundreds of miles around France. They even built one on the French coast to enable easy communications with Britain after the forthcoming invasion. As it happened, they never did manage to invade, so the British end of the link was never constructed. During this time the British were busy building their own set of towers of a slightly different design to connect the Naval Headquarters at London with the south coast ports. They were also busy trying to burn down the French towers.

During the next 20 years, over 1000 towers were built across Europe.

Yes, very nice, but it could be faster

For speed, ideas were returning towards electricity. We had the usual crop of interesting but impractical ideas. There was one in which the ends of 26 wires were dipped in acid and, when energized, bubbles would appear and the letter could be deciphered.

Francis Ronalds set up a working electric telegraph system around his garden which used a clock similar to the Chappe casserole lid method except that a burst of electricity moved a...

Produkt-Details

• Erscheint lt. Verlag: 19.9.2002
• Sprache: englisch
• Themenwelt: Mathematik / Informatik ► Informatik ► Netzwerke
• Themenwelt: Naturwissenschaften ► Physik / Astronomie ► Elektrodynamik
• Themenwelt: Technik ► Elektrotechnik / Energietechnik
• Themenwelt: Technik ► Nachrichtentechnik
• ISBN-10: 0-08-049580-X / 008049580X
• ISBN-13: 978-0-08-049580-4 / 9780080495804