About Base Stations, Radiation and Foil Hats

It often happens that as soon as the antenna of the cellular network is installed on the roof of a residential building, complaints from tenants immediately begin. There are some standard ones like “I started to get a headache!”, And there are such interesting ones as “They stopped giving birth to cats”, “All cockroaches died out” and even “They started following me!”.

Clearly, the new thing is to blame. In some cases, due to such complaints, the base station doesn’t get directly switched on, and the antennas that have been mounted, but not yet put into operation, have to be removed and transferred.

Below, I will tell you how the base station emits and make calculations.
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What is dangerous

The danger of radio waves for the human body is not fully investigated at the moment, but research is being carried out, you can read about them, for example, here in the section “How the EMF affects health”. In general, if you analyze the research, it becomes clear that yes, it is dangerous !

What is being done to avoid this danger? In our country there is a standard by which, in particular, the construction of base stations is carried out. In SaNPiN 2.1.8 / 2.2.4 it is written that the maximum permissible energy flux density for the frequencies at which our BSs operate (900, 1800, 2100 MHz) is 10 μW / cm ² , or 0.1 W / m ² . It is from this number that we will continue to make a start in assessing.

In fairness, it should be said that in many Western countries such norms allow local population to be irradiated with energy flux density a couple of orders of magnitude higher, about 1 mW / cm ² , that is, 10W / m ² .

Estimate of actual exposure

So, we have a number, above which you can not jump in any case. How can you understand whether the radiation specifically in your apartment / office will be higher or lower than this value?
First, what is this very energy flux density? This is how much radiated antenna energy will pass through a certain area (cm ² in SaNPiNe). If the antenna radiated equally in all directions, then all the energy would be smeared over the sphere around the antenna. Well, such antennas are not particularly needed by the cellular operator, we most often use directional sector panel antennas that radiate in a certain direction (radiation patterns can be found in the manufacturers' antenna catalogs, for example, here ).

Here is a typical radiation pattern:


<sup>Horizontal (left) and vertical radiation patterns on a logarithmic scale.


Horizontal (left) and vertical radiation patterns in the usual linear scale.</sup>

Well, the very density of the flow of energy can be calculated if you look into any book on radio engineering.

And now with examples

First of all, the easiest option - put the antenna on the house opposite, what will happen if she looks directly at you, unprotected with nothing (even a foil cap)?

With conventional antennas, the gain in the main lobe of the radiation pattern is, for example, 18dBi (this is 63 times). Suppose the antenna goes to the input of the antenna as much as 40 W (this is rarely used, usually not higher than 20 W, but it is possible to exaggerate for evaluation).

Then the energy flux density with the distance will fall as in the picture:


Here the blue - restrictions on SaNPiN. It turns out that at a distance of 45 meters from the antenna it is already possible to be at least round the clock and, according to sanitary standards, it will be absolutely harmless to our health.

Let's take a more realistic case, when the BS is installed on the house opposite, but there is a pane on the way between you and the antenna (it attenuates the signal by 4dB, that is, 2.5 times). Even concretize, take your example - the house across the road, on which stands the BS, according to Google Earth between him and my windows 110 meters. In this case, we get that when I eat, I get 0.0066 mW / m ² . This is 15 times less than the limit level - you can safely eat without hiding behind the fridge!

More often it happens that you and the antenna are not separated by glass, but by a wall. In reinforced concrete walls, the signal attenuates even more, most often it is about 15dB (almost 32 times).

This is what we saw, what would happen if the antenna was sent directly to you, that is, specifically aimed at your apartment / office.

More often, you are not in the main lobe of the radiation pattern, where the radiation is maximum, but somewhere on the side, where the antenna gain is already noticeably lower than 18dBi. In these cases, of course, the radiation will be even lower, for example:



A rather frequent situation is illustrated here, when the antenna is shining above the subscriber, and it is served by the lower lobes of the radiation pattern. In the direction shown, the antenna gain is 24dB ( 250 times ) lower than the main lobe level.

Well, now back to our example from the very beginning: what if the antenna was installed on the roof of your house?

Then the antenna gain in the direction of the apartment on the top floor will be approximately -5dBi (attenuation 3 times), the ceiling will give attenuation of 15dB (32 times). If we calculate, we get that cats that stopped giving birth and dying cockroaches at a distance of 2 meters from the antenna receive 0.0078 W / m ² , that is a little more than me, eating 110 meters from the antenna.

What does this mean, cap?

If the base station is over your head on the roof, almost nothing comes to you. On the other hand, if you decide to climb on the roof and turn on the sector antenna, and then sunbathe under it, a very unpleasant surprise awaits you.

Ahhh! I have a femtochka on the table, what should I do?

If we talk about femtocells, about which there was a conversation in one of the previous posts, then their power does not exceed 0.1W, which is 23dB lower than the power of the example we considered. They are also characterized by an omni-antenna, the gain of which is much smaller than panel antennas (about 2-3dBi). With such calculated values ​​already in 1m from the femtocell, the signal level is 10 times lower than the norms for SaNPiN.

Paranoid note

1. You should not hug with the included base station. At least for a long time - for sure.
2. Do not keep the femtocell on your lap and on your desktop. Guaranteed safe distance from it to you - 1 meter on either side.
3. Categorically you should not get into the focus of the radar at various military sites: the power there is several times higher.
4. The radiation from the BS in the neighboring house is at times less dangerous for health in comparison with the periodic radiation of the Chinese microwave (where it strikes from all the cracks). Factors comparable in power with BS radiation right on the roof above you are the usual home Wi-Fi and Bluetooth headsets.

About our employees

As for our employees, during planned work, when they approach directly to the antennas and can receive already noticeable harm, it is customary for us to disconnect the BS for the duration of the work.

findings

From the above, it can be understood that practically any feasible option for installing base station antennas is harmless to humans (if you believe SANPiN). If we recall that 40 watts of power are fed to the antenna very rarely, then it becomes even easier for the soul. Plus, it is worth remembering the norms in most Western countries, where the dangerous level begins much higher.

PS: I can tell in the comments how to measure the radiation density at home or in the office.
Upd. : the promised told