Assuming the propagation follows the inverse 4th power-law what is a reasonable power value in W, to assume at a distance of 540 m from the BS Express your answer in scientific notation to 2 decimal places.

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If we assume a directional antenna with gain of 17 dB 50, then the distances required in certain directions could require a multiplication factor of sqrt(50)7.

The inverse square law states that the magnitude of ones exposure drops dramatically, proportionally to the square of ones distance from the source.

The purpose of the calculations below is to demonstrate that the inverse square law (defined at right) is not as helpful as you may think, when the level at which health effects occur is far below the transmit power of the devices (and international standards).

Sleeping with an alarm clock within one foot of your head is like having ones personal electricity tower.

Windows with low-E coating or low-E films, concrete, and brick, may provide higher levels of attenuation, and are not factored into the calculations below.

For approximate purposes, the numbers calculated below assume an isotropic antenna with uniform intensity.

For directional antennae, we must factor in gain to calculate the maximum required distance.

The distances in this section may need to be additionally adjusted by multiplying the distances by the square root of the gain.

This multiplication factor might vary anywhere from 1.3 to 7, depending upon the antennas gain.

The following presentation by Graham Philips shows that a Wi-Fi enabled laptop at 50 cm can provide more radiation than a mobile phone mast (cell tower) at 100 meters (See slide 13).

According to the Table of Effects mentioned above, some effects are still seen at the Salzburg(2001) limit.

Hence, the Salzburg(2002) limit is preferrable, or somewhere in between.

Some wireless routers allow you to reduce the transmitting power, and even schedule the hours during which Wi-Fi will be turned on.

For example, one particular model provides 10 levels of power, allowing one to drastically reduce the strength.

Hence, its peak output power is comparable to a mobile phone.

To reduce the duration of exposure, turn off data services like Mobile Data and Wi-Fi except when needed, turn off Background Data, or increase auto-sync intervals, and avoid use where signal reception is weak.

Although speaker mode or a wired headset at 1 meters distance greatly reduces the power density, it may not be enough to achieve the precautionary limit.

For more information on smart meters, see What is a Smart Meter.

The power density can be estimated using the equation PG4r 2, where G is the gain from the directional antenna and 4r 2 is the surface area of a sphere.

In practice, the cell tower radiation is not usually isotropic but is directional with main lobe and side lobes.

Note that a directional antenna focuses the power in certain directions, resulting in higher required distances.

Inverse Fourth Power Law