Posts Tagged ‘aerials’
January 7th, 2009 | 
Author: The phenomenon of electromagnetic induction was first discovered by Michael Faraday in 1831, and it is evident that he realised at least a part of its future potential in the modern world. A contemporary politician asked him about the usefulness of the discovery; he answered ‘at present I do not know, but one day you will be able to put a tax on it.’
The earliest record of using electromagnetic technology to locate buried cables dates from around 1910. More portable locators were made over the next years and the Sharman Main Finder was just one example. The user instructions give a tinge of envy to anyone trying to trace gas pipes .. ..’just clip the generator to a gas bracket in the nearest house or onto a street lamp.’
American and German schools of design emerged during the years leading up to the Second World War. In North America roads were wide and wide cables hung on poles so the main requirement for a locator was to locate widely spaced buried pipes. The result was a simple, high frequency, low power and low cost locator.
In Germany, cables as well as pipes were buried under narrow streets, so elaborate low frequency and high power locators were developed that required considerable expertise to obtain satisfactory results.
Dr Gerhard Fisher of California designed the Metallascope, the first high performance buried pipe and cable locating set. His system made use of the latest scientific developments and his company exists today and still produces the M-scope, an up-to-date descendent of the original Metallascope.
One of the engineering sections of Bell Laboratories studied the problem of accurate location of newly buried cables and recognised that an antenna with twin sensing aerials would give more positive plan definition, and also measure the depth of a target cable. The subsequent design, called the Depthometer, was engineered and manufactured in 1964. It was another 12 years before the first commercial twin aerial antenna locator was made by the Electrolocation company in Bristol England.
The twin aerial system was found to have substantial advantages over single aerial locators. Twin sensing aerials combined the seemingly contradictory qualities of discrimination with sensitivity. For the first time it was possible to locate buried cables below an overhead power line and to sort out crowded utility services under a city street intersection.
The introduction of the twin aerial antenna coupled with miniaturised electronic circuitry coincided with a programme of extending and upgrading utility distribution systems. This growing demand and technical progress resulted in a series of advances and new features to make locating more certain and more simple. Some of these advances included:
” Combination of active and passive signal reception
” Multi-frequency locating sets enabling the user to select the most suitable frequency for each application
” Electronic depth measurement.
” Current measurement along the length of a pipe or cable to detect coating or insulation defects.
” Current direction recognition to verify the identity of a target line.
” Permanently installed signal transmitters to apply a signal tone to a telephone cable over distances up to 150km/100 miles.
Today, electromagnetic locators are the worldwide standard for locating buried pipes and cables. A number of specialised manufacturers offer a choice of locators ranging from simple equipment used to detect the presence of buried cables to sophisticated instruments for pinpointing, identifying and fault finding buried pipes and cables in the most complex situations.
Written by Select Surveys, one of the UK’s leading independent surveying companies specialising in using electromagnetic, CAT and ground penetrating radar equipment to detect underground cables and utilities.
Article Source: A History of Underground Electromagnetic Surveying
The Great Digital Switchover has been talked about for a few years now but, for television viewers in some parts of the UK, it is happening within the next few months. Here’s what you need to know..
Since the birth of television in Britain, pictures have come into our homes in signals picked up by our televisions aerials, using analogue technology. Now, because this is no longer an efficient use of airwaves and only contains enough room for a small number of channels, the government has decided to switch off the analogue service in favour of introducing digital services to everyone. At the moment, only about three quarters of us live in areas where digital signals can be received. The only way the rest of the population can get them is by switching off the analogue ones. Then, at least 98.5% of us will be able to tune into digital channels via our aerials.
There are a number of significant benefits for viewers arising from this change. Generally, for example, digital signals are far more reliable than analogue ones, meaning a better picture, and there will be an increase in the number of available channels.
In order to be ready for the digital switchover, you have to ensure that your TV can receive the correct signals. As a rule of thumb, if you can already watch more than five channels, your television is probably already digital. If not, you will need to either replace it with a suitable TV or get a digital set-top box. This will need to be done for all your televisions, that little portable in the bedroom included! It needs to be stressed that the old analogue transmitters will be switched off, so you won’t be able to keep on watching unless you have the correct equipment. It’s important to stress that the digital switch doesn’t mean we all have to rush out to buy a satellite dish, the signals can be picked up by aerial, cable or broadband as well as by satellite.
People in Whitehaven, in Cumbria, were the first to be digitalised, in 2007, and gradually the rest of us will follow. Your change date depends on the ITV region you live in, with Border, The West Country, Granada and parts of Wales switching in 2009 and Meridian, London, Tyne Tees and Ulster being the last to change in 2012.
If you’re over 75, or eligible for disability living or attendance allowances, or mobility supplement or you are registered blind or partially sighted, there is a help scheme for you which is free if you get pension credit, income support or job-seekers allowance. Digital television will bring many benefits to television viewers, it’s just a matter of making sure we’re geared up and ready for the switchover when it comes to your home area.
You may already be aware of what you need to do for the switchover, and you may be considering getting high definition television and taking full advantage of its HD ready capability. You can find out how to get HDTV today.
If you’re looking to replace your equipment, a new digital LCD TV might be just the thing you’re after. Take a look at the wide range of full reviews available for the latest Sony LCD TVs
Article Source: The UK Digital Switchover.