Point to point microwave links are a core element of telecommunications infrastructure. They carry digital data at the speed of light between two antennae typically spaced a few kilometres apart. These links rely on a clear line of sight between the link ends as well as within a Fresnel Zone around the link path. Links will cease to operate if they are blocked by physical structures such as tall buildings. The changing shape of our cities often means buildings stop links working with the affected links having to be redesigned or replaced.
Figure 1 30 St Mary Axe London a.k.a. The Gherkin
Microwave Links in the United Kingdom
The chart below shows an example plot of licensed microwave link paths in central London. Each square on the chart has an area of one square kilometre. Nationally there are around 31,000 links which means that any new city centre development has the potential to block microwave links and cause them to fail.
Figure 2 Point to Point Microwave Link Paths – Central London
Assessing Microwave Link Impacts
To assess whether a building development is likely to interfere with a particular link it is necessary to determine where the link ends are and what the link frequency is. This enables the dimensions of the Fresnel Zone to be calculated as shown in the diagram below.
Figure 3 Calculation of Fresnel Zone Radius
Two dimensional and three dimensional calculations can then be undertaken to see whether the proposed development is likely to adversely affect operation of the link. Sometimes it is necessary to survey link ends to determine their exact positions.
Tools for aiding such assessments include clearance charts, clearance calculation sheets and GIS shape files of link exclusion zones.
Where a conflict between a building and microwave link occurs it is usual for the building development to go ahead which means that its future impact on the link will need to be mitigated. This can be achieved by:
- Rerouting the link so it no longer passes near the building
- Repositioning a link end to ensure the link clears the building
- Replacing the radio link with a fibre optic link
- Redesigning the data network so that the link is no longer required
- Replacing the exiting link with a new higher frequency link – this will reduce the size of the Fresnel Zone and can thus enable the link to clear the building
How can Pager Power help?
We can provide telecommunication impact assessments which include consulting with link operators; identifying potential microwave link issues; undertaking microwave link clearance calculations and helping provide all of the data necessary to support a planning application – showing that potential microwave link issues have been managed and resolved professionally.
For further information contact Mike Watson on 01787 319001