- Julie Bergeron
- Charles Rousseau
Transmission Spectrum Engineering
Most of us are familiar with Google Earth and its ability to let anyone navigate anywhere around the globe and view satellite imagery, maps, terrain, buildings in 3D, and the like. Google Earth is an application that can easily be used by everyone.
CBC/Radio-Canada's Transmission Engineering team has found a way to leverage Google Earth's capabilities and use it as a broadcast engineering tool and, at this point, it is our clients and stakeholders that benefit the most from this application.
Google Earth allows users to save cartographic data and other information to *.kml and *.kmz files; using these files, engineering data can now be shared easily and quickly with anyone who may be interested within the organisation.
The Transmission Engineering team uses Google Earth for three major tasks: coverage planning, FM and Digital Television (DTV) field strength measurements, and Safety Code 6 measurements. Traditionally, the outcome of this work was shared with multiple static maps, usually presented in a *.pdf format. Each map required the engineering staff to put considerable time and effort into it; however, thanks to Google Earth, these maps can now be replaced and all the relevant information can be provided in one single, well-organised file.
One of the key fields of expertise of the Transmission Engineering team is coverage planning of CBC/Radio-Canada's over-the-air television and radio services.
It is within the context of this process that the team ensures that the parameters of the station under study, such as its transmitter power, antenna gain, height of the centre of radiation, and radiation pattern are optimised to best serve the area to be covered.
Figure 1 – CBC Radio One – Tillsonburg, ON Repeater
In the example shown in Figure 1, one can observe the coverage of three Radio One stations in Southern Ontario. The station on the left, CBCL-FM in London, and the one the right, CBLA-FM-2 in Kitchener, are existing stations. The one in the middle is a proposed repeater to better cover the city of Tillsonburg. The contour lines are the traditional F(50,50) curves, also named protected contours by Industry Canada. The green and blue fill (or splatter) is the realistic coverage of the three stations. The realistic coverage was simulated using a propagation model that takes into account the terrain level and clutter (forest, water, urban, dense urban, etc.). Note that the blue splatter corresponds to the area where the received signal strength is expected to be 54 dBµV/m or higher, alternately, it is where one would have reliable reception in a rural area. The green area is where the signal is expected to be 70 dBµV/m or higher. A stronger signal is particularly important to provide good in-building reception in urban areas.
Using the Google Earth application, it is possible to add or remove the stations' coverage areas just by clicking on the layers in the Places menu on the left of the Google Earth window. One can also modify the opacity of the realistic coverage zone in order to have a better view of what lies behind the blue and green splatter by selecting the appropriate layer and then using the Adjust Opacity tool located on the bottom of the Places menu. This allows one to precisely visualise which communities are served by the radio coverage and which are not.
Amongst other things, these dynamic features have allowed the Transmission Engineering group to become really efficient in providing coverage recommendations. Please feel free to try the tool yourself by downloading the coverage-planning map of Tillsonburg and southern Ontario. Download the Radio One – Repeater Analysis – Tillsonburg, ON
The Google Earth application is required to view the map; you can download it for free (for personal use) at http://www.google.com/earth/.
Field Strength Measurement Analysis
When a new broadcasting station is put on the air, the Transmission Engineering group often conducts RF field strength measurements to validate its coverage. These measurements demonstrate whether or not the transmission site performs according to the planned parameters of the engineering brief authorised by Industry Canada. These measurements are made using a car with a dipole mounted on its roof, an automatic field strength meter, and a GPS. This setup allows the amplitude of the electric field at the chosen frequencies to be measured and the corresponding geographical coordinates to be tagged. Measurements are taken every three to five seconds. Once the survey is completed, the measured data is simply exported to Google Earth and layered on top of the coverage simulations.
Once all of the data is packaged into a Google Earth file, it can be attached to an engineering report for immediate or future reference, or it can be simply sent as an e-mail attachment. At that point, anyone, from the engineer or technician to the station director, can use it to perform in-depth analyses. The search tool embedded in the software allows a user to locate and identify streets, addresses, or villages in which the user might have an interest. Given that a picture is worth a thousand words, you can only imagine how much a dynamic map combined with a search tool is worth. Granted, the precise figures are not immediately quantifiable, but the Canadian taxpayer can rest assured that the savings are substantial, both in terms of time and effort.
Please click the following link to view an example of field strength measurement analysis centred around a CBC Radio One station located in Leamington, ON
Download Radio One – Leamington – CBEW-FM-1.kmz., that went on air during the fall of 2010.
Figure 2 – Field Strength Analysis for CBEW-FM-1, Radio One in Leamington, ON
Safety Code 6 Measurements
Figure 3 – Narda SRM-3006 – Used for
Safety Code 6 Measurements
Safety Code 6 is the document establishing the safety limits for human exposure to RF energy in the frequency range from 3 kHz to 300 GHz. All broadcasters have the on-going responsibility to ensure that the general public will not be exposed to RF energy emitted from their antenna installations that would exceed these limits. In order to do so, CBC/Radio-Canada performs measurements at its transmission sites and provides reports to state their compliance or to recommend corrective measures when required.
Currently, the Transmission Engineering group uses Google Earth to display Safety Code 6 measurement results in a user-friendly environment. Thanks to the use of a data-extraction application developed internally by Pierre-Alexandre Nolet, a Junior Engineer working with the Transmission Engineering team, engineers can now export measurement data from the Narda SRM-3006 to a Google Earth file in only a few simple steps.
Once this file is opened in Google Earth, it is then possible to click on any given point to visualise the list of all frequencies measured with their RF contribution indicated as a percentage of the Safety Code 6 limit, which greatly facilitates the site assessment. Additionally, with this process, Transmission Engineering has shortened the time between the end of the measurements and the beginning of the analysis to a few minutes.
Please click on the link below to view the measurement campaign performed at the Mont-Bélair transmission site in Québec, QC
Figure 4 – Safety Code 6 Measurements at Mont-Bélair, QC
Figure 5 – The Places Menu, Google Earth
Although Google Earth presents numerous advantages, it also has its limitations. First of all, the application requires an Internet connection in order to access Google's databases. Without an Internet connection, the software will only display the information currently stored in its memory cache and the search tool will not work. Therefore, unless one had recently viewed a location of interest, Google Earth will not be able to display it accurately.
The Transmission Engineering group believes that Google Earth is fairly easy to use for people with a technical background or with basic computer skills. However, not everyone in the broadcasting industry has the same grasp of software applications and there is a learning curve associated with the software. For example, one must learn to navigate in a 3D environment if one is not already familiar with that sort of context. Furthermore, one must pick and choose the data relevant to the analysis in the Places menu. By clicking on the top folder, all of the file's information will be displayed, which, in some cases, will result in the user only seeing a blur of information; as you can imagine, this is not always convenient.
Finally, as impressive as Google Earth is, it cannot replace everything; it is not a single solution to all mapping endeavours. The *.kml and *.kmz files are not official documents and Google's terms and regulations prevent anyone from printing a map using their satellite imagery as a map background. Consequently, traditional static maps, commonly presented in *.pdf format, are still required for a lot of applications, such as engineering briefs for radio or television station applications.
Google Earth has proven to be a great tool that significantly improves the efficiency of CBC/Radio-Canada's broadcast engineers, and there is no greater proof of that than the fact that the Transmission Engineering team now produces over 60 engineering reports per year. Moreover, these reports are clearer than ever before and the benefits are not only for broadcast engineers, but also for the group's clients and stakeholders, as they are now able to use Google Earth to have a better understanding of the various coverage analyses, simulations, measurements, and recommendations provided by Transmission Engineering on a daily basis.