Measured and by antenna picked up power, here -30 dBm, can be assumed that it is in same range as amount of power that can be picked up by a human body at similar distance.
It is dangerous as it is EM waves transferring energy which is creating heat when these waves are absorbed in skin and fat close to surface of human body.
It is easy measured with a simple thermometer how much skin-temperature is increased.
Human body have inbuilt functions trying to handle local heating. Typical methods is by increasing blood flow to spread heat more even over a bigger area and then emit that heat with aid of sweat transpiration.
More intense heat and body reacts with reflexes trying to avoid touching a very warm surface, such as a hot soldering iron.
Measured amount of power is less then -30 dBm. It corresponds to 0.000001 Watt
Assume a human body can absorb ten times more power then your antenna, it is ten times more effective as antenna, and resulting absorbed power is 0.00001W.
We can compare this to other sources of same kind of EM waves.
A 1W flashlight pointing against directly at your body makes your body receive 100.000 times more radiation and it will induce much higher levels of heat locally at your body. Depth of radiation under your skin is similar as for 900 MHz EM waves, 99,9% of all radiation is absorbed within 10mm below skin, but heat will continue to spread deeper even after flashlight is turned of.
The biggest and strongest local EM source we know about is hanging outside, our sun. At a clear day will sun emits peak 2000W/m² at earth surface. As an adult human body expose about 1 m² of surface against sun if not using protecting clothes can we absorb up to half of that 2000W and the other half is reflected if it is a pale skin. Absorbed amount of power is then then about 1000W. Really a lot of heat to handle. Body internal cooling system have to run as hard as possible to avoid permanent harm and adding as much coolant liquid as possible is often important a sunny and warm day.
As with all kinds of radiation is time a critical factor when comparing resulting radiation wounds.
Say that a terrible accident happen and you get exposed by sun for 1 minute totally unprotected. Amount of absorbed energy in your body is then equal to amount of energy absorbed 3m away from your repeater during a period of 1900 years.
Turn it the other way, avoid sun for one minute and you have compensated for your router RF radiation for 1900 years.
As radiation levels decay with square of distance, keep at least 50 meter distance from heating elements inside house.
A kitchen stove can easily emit a 2000-3000 Watts and the closer you are, the bigger risk for burning wounds.
Burning risk is here a factor exactly same as for a flashlight or a cellphone which can emit up to +30 dBm (1W), about 1 million times stronger then your measured -30 dBm from repeater.
If measuring a active cellphone from 3m distance will probably show similar result as for the router.
Difference is that cellphone is often held at a much shorter distance then 3m.
Be also aware of risk due to EM waves radiated from light bulbs indoor. They emits often more then 10W, not seldom close to your eyes.
Even worse, a computer screen is sending waves directly against your face and eyes, not seldom with 50W or even a bit more, including IR waves.
EM waves are causing heat effects but with increasing frequency increase level of sporadic harm at atomic level. A such harm is when a subatomic particle is kicked away from its atom, a first step to cause permanent cell modification. That danger increase with frequency. For frequencies corresponding to visible light-waves is it almost never possible to kick atomic particles away from its atom as needed energy level is too high.
For next known frequency range upward, UV-waves is it more possible and at even higher frequencies, x-ray, is it potential even more harmful as almost all radiation now is in shape of particle radiation and no EM waves.
It is same type of X-ray that is radiating at us in higher amount when traveling with airplane or when examine teethes at dentist.
For real low frequencies, almost DC, such as 900MHz which is at least a million times lower frequency then UV is it really not even possible to kick away an electron from its atom as needed energy level to do so not is even theoretical is possible.
Even lower frequencies with high radiation levels found in in many houses is in frequency range 50 or 60 Hz and is emitted in real high amount as magnetic radiation. Human body is way to short antenna to become an absorbent of energy at these wavelengths. Only possible way to absorb energy at these frequencies is by direct connection between electrical wires and body.
Even at real small distance between an electrical wire and skin, and transferred energy is much reduced.
From above examples, it is a clear relation between EM wave frequencies and human body efficiency as a wireless receiver.
Question "is GSM booster radiation levels safe for health" can with above text now be better put in perspective.
The booster consumes probably 10W but emits max 1W at relative safe frequency, 900MHz. It is the remaining 9W that are more dangerous as they not just goes up in smoke, but are emitted as heat-loss within IR-range, which is much more dangerous due to its higher frequency compared to 900 MHz. IR is slightly less harmful then light bulbs that radiates mainly at higher frequencies but as it is around 400 THz is it 400 times higher frequency then 900MHz.
If radiation levels corresponding to a 10W light bulb or more not exist inside your house, and if all window are blocked from sunlight entering inside house and emits its radiation, yes heat loss from your repeater, all 10W of it, are a risk for your health as it now a dominating radiation source in your house, as long as it not is any human bodies inside house as such emits a lot more radiation.
If absolute no radiation sources exist inside your house, it is a disadvantage as temperature then not can go above absolute zero, -273C.
To keep temperature in balance must human body and its surrounding constant absorb about same amount of radiation as it emits.
A human body will die within a minute without any external radiation.
Your body is a radiation source, emits 100W or more of heat that may be absorbed by other human bodies. Emitted in IR range. Your body is also a dangerous wave-converter, as it converts absorbed less harmful 900MHz radiation to IR-radiation that then can be re-emitted to surrounding environment.
Avoid radiation emitted from other humans and avoid sun-radiation, both are scientifically proved dangerous for your health.
Health problem due to GSM-repeater is harder to measure as its radiation level often is so much weaker then more possible harmful radiation sources in same room, such as a light bulb or a heating element, which is assumed to be relative safe.
Why fear 1000W at 900MHz, causing about same amount of heat radiation as a conventional electrical heating element at that amount of power?
Government regulation related healthy or unsafe radiation level are all based on guessed fear level, as it not exist any scientific prof in any direction for any disease or harm, except for known facts that EM-waves absorbs as heat and nothing else.
Our strongest source of all sorts radiation, the sun, is however less regulated.
Radiation-levels levels from sun is known that we can survive for at least shorter periods, which is our practical health level.
Even hotter or sunshine for too long period is uncomfortable,. Can cause dangerous dehydration and skin burn.
With low amount protecting ozone can UV-radiation from sun faster reach dangerous levels at which permanent cell-wounds can occur. Most of these wound are repaired automatically. If not, can it result in dangerous health problem.
Eyes is a special problem. Eyes can be burnt by sun at an even shorter time then skin as an eye can focus radiation to a smaller spot, causing short period with high intensity of radiation in bottom of eye. That kind of wound can not allways be repaired by body itself or by doctors..
That problem does not exist at 900MHz as wavelength is too low to be focus-able with an optical lens.
Government regulation regarding allowed RF-levels and frequencies, to avoid interfere other equipment or blocking frequencies used for important communication should be respected.
On the other hand, if living in a very rural place where radio/telephone/TV-signals are weak due to long distance or blocking terrain and no neighbors, will signals you equipment generate be equally blocked in other direction by same terrain.
Airplane communication can still be interfered even from a rural place, but it is a seldom reported problem.
Known such interference with airplane communication have been mostly close to airport, near or at ground.
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