Radio waves
- i.At 150m from the antenna of a cellular base station in open country, measurements show that the power per square metre is 200µW m-2. What power per square metre could be expected at 300m from the base station? Show your working and explain any assumptions you make
- ii.A base station is located in an urban environment, and the power per square metre at 150m is measured to be 3µW m-2. What would be a reasonable value to expect at 300m? (You will have to make an assumption to calculate your answer. State the assumption that you make.)
- iii.explains that urban environments are more obstructive to radio waves than rural environments, reducing the range that a single base station can cover. This turns out to be an advantage in urban areas with high demand for cellular communication services. Briefly explain why reduced range is advantageous in this context.The maximum word limit for Question 2(b)(iii) is 100 words.
At 150m from the antenna of a cellular base station in open country, measurements show that the power per square metre is 200µW m-2. What power per square metre could be expected at 300m from the base station? Show your working and explain any assumptions you make
Area of the circle = π r²
Therefore the area of the circle at 150 metres = π( 150²) = 22,500 π m²
Total power = 22,500 π m² * 200µW/m² = 45 × 10^5 π microwatts
The total wattage will be distributed over a large area at 300 m.
Thus Area = π (300²) = 90,000 π m²
Total watts/ area = (45 × 10^5 microwatts) / 90,000 π m²) = 50 microwatts/m²
The power per square metre expected at 300 metres is 50µW. Research by Suzuki (1977) provisions that an illumination effect will change in inverse proportion to the square of the distance from the light source.
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