ADSL

Asymmetric Digital Subscriber Line. A DSL, or Digital Subscriber Line, commonly transfers data to and from a subscribers premises by 'piggybacking' onto existing infrastructure, most commonly a standard analogue BT telephone line. Existing mains power supply cabling is sometimes utilised, also satellite or proprietary cabled networks. The data transfer is carried out by means of a high-frequency 'carrier' which does not interrupt the normal working of the existing service used as the vehicle for transmission. Data transfer is divided into two components - transmission and reception. In Asymmetric transfer (ADSL), one (usually transmission) is carried out at a slower rate than the other.

Blown Fibre

Empty micro-ducts are pre-installed on-site. As, and when required, fibres are blown into place with compressed air.

Chromatic dispersion

Pulse spreading in an optical fibre caused by variations in light propagation with wavelength. The sum of waveguide dispersion and material dispersion.

DWG

The standard file format for saving vector graphics from within AutoCAD

DXF™

An ASCII or binary file format of an AutoCAD drawing file

DWF

A highly compressed file format that is created from a DWG file

Raster Graphics

An image file format that consists of a rectangular grid of small squares or dots known as pixels. For example, a satellite photo, scanned image, or fax. Examples of raster formats are bitmaps and JPEG files.

GPS

The Global Positioning System (GPS) is a worldwide radio-navigation system formed from a constellation of 24 satellites and their ground stations

GPS uses these "man-made stars" as reference points to calculate positions accurate to a matter of meters. In fact, with advanced forms of GPS you can make measurements to better than a centimetre!

In a sense it's like giving every square meter on the planet a unique address.

GPS receivers have been miniaturized to just a few integrated circuits and so are becoming very economical.

Here's how GPS works in five logical steps:

1. The basis of GPS is "triangulation" from satellites.
2. To "triangulate," a GPS receiver measures distance using the travel time of radio signals.
3. To measure travel time, GPS needs very accurate timing.
4. Along with distance, you need to know exactly where the satellites are in space. High orbits and careful monitoring are the secret.
5. Finally you must correct for any delays the signal experiences as it travels through the atmosphere.

D.G.P.S

Differential GPS involves the cooperation of two receivers, one that's stationary and another that's roving around making position measurements.

The stationary receiver is the key. It ties all the satellite measurements into a solid local reference.  

C.D.M

Construction (Design and Management) Regulations 1994.

The CDM Regulations are aimed at improving the overall management and co-ordination of health, safety and welfare throughout all stages of a construction project to reduce the large number of serious and fatal accidents and cases of ill health which happen every year in the construction industry.

The CDM Regulations place duties on all those who can contribute to the health and safety of a construction project. Duties are placed upon clients, designers and contractors and the Regulations create a new duty holder - the planning supervisor. They also introduce new documents - health and safety plans and the health and safety file.

See site for details:http://www.hse.gov.uk

Multimode fibre

Optical fibre with a core size that permits propagation of non-axial rays. Usually described by referring to core diameter

and cladding diameter, e.g. 62.5/125.

NRSWA

The New Roads and Street Works Act 1991 (NRSWA) controls and co-ordinates work carried out in the street by undertakers. For the purposes of the New Roads and Street Works Act, all Utilities are defined as Undertakers. Undertaker’s also include those granted a street works licence by street authority.

Optical Time Domain Reflectometer (OTDR)

An instrument that measures transmission characteristics of an optical fibre by sending a short pulse and measuring the return signals resulting from backscatter and reflections.

Singlemode Fibre

A low loss optical fibre with a core diameter of 2 to 8 microns. Only one mode is transmitted at the wavelength of interest.