Measuring electric field vs magnetic field

[aphelix]

Hello.

Sorry. I am not a physicist and I have very superficial knowledge of the subject. I would like to ask a question about the practical field. I only have a device that measures the electric field. When I measure the signal coming from a cell phone tower before it is reflected from a metal garden fence (completely covered, not wired), I read 3 v/m. When I measure it after reflection at the appropriate angle, I see that it has dropped to 1 v/m. Has the magnetic field value (ex. microtesla) also decreased by the same amount? Or could the magnetic field be different?

Thanks.

 

[WernerQH]

Has the magnetic field value (ex. microtesla) also decreased by the same amount?

Yes. To convert E to H, you divide by $377~\Omega$, to convert to B you divide by the speed of light. For 1 V/m I get H = 2.65 mA/m and B = 3.34 nT.

 

[sophiecentaur]

Yes. To convert E to H, you divide by 377 Ω,

But only in free space. The impedance of the regions near the ground or any conductor will not be 377Ω.

Has the magnetic field value (ex. microtesla) also decreased by the same amount?

Firstly, why would you need to know that?
Then. where are you measuring this 1V/m? The measured value is likely to be due to the resultant of the incident and reflected wave and could have maxes and mins all over the region. Also the polarisation will probably vary with position.

 

[aphelix]

Firstly, why would you need to know that?
Then. where are you measuring this 1V/m?

I have a Wavecontro SMP2 device, equipped with a high-frequency signal probe capable of measuring signals up to 8 GHz. However, it can only measure electric fields. When I position myself directly to the cell tower, just in front of a metal garden fence, the measured value reads 3 V/m. If I step back 5 meters from the fence to my house walls, and face away from the tower towards the fence, the reading decreases to 1 V/m. But the tower couldn't be seem from there.

The primary concern is that my son's room is located there, and I want to determine if it is affected by the signal. The fence is approximately 4 meters high and is made of metal.

when I measure the electric field right in front of his room's window(towards fence), the reading registers as 1 V/m.

 

[WernerQH]

The power reduces to 1/9 when the field drops by a factor 3. For the case of 1 V/m the radiated power is E×H = 2.65 mW/m^2. Only a fraction of that is absorbed by the human body (depending on frequency), but even if it were 100%, the absorbed energy would be five orders of magnitude below the heat produced by the normal human metabolism (about 100 W).

 

[f95toli]

Also, if you or your son have a mobile phone or wifi, the power from these will be comparable to that from the tower inside your house.
Moreover, whenever you are outside in your garden you will be exposing yourself to a much, much more harmful type radiation that is a major cause of cancer: namely UV radiation from the sun.

 

[sophiecentaur]

I have a Wavecontro SMP2 device, equipped with a high-frequency signal probe capable of measuring signals up to 8 GHz. However, it can only measure electric fields.

There are very good, practical reasons for this. The main one is that the majority of users are only interested in one field reading. When assessing signal strength for comms, the standard E field measurement is convenient and easy to reproduce and allows calibration of measuring equipment. The same thing also applies to measuring Hazards. I suspect this is the context of your post.

I searched around for some figures about acceptable levels of RF for humans and was pretty swamped with information as it's different for all frequency bands and different levels are chosen in different administrations. You will need to do your own homework on this, I'm afraid. Many people worry about exposure to RF from local transmitters and there are many cranks involved with the argument so be careful what you believe.

As you already have the measuring device, you could walk all over and around your home and see what happens to the readings - also go right up close to the mast. The beams are usually shaped so that there is very little power directed towards local ground. Your results could be interesting.

Is there a local protest group against that particular mast?

Good luck.

 

[sophiecentaur]

The power reduces to 1/9 when the field drops by a factor 3. For the case of 1 V/m the radiated power is E×H = 2.65 mW/m^2. Only a fraction of that is absorbed by the human body (depending on frequency), but even if it were 100%, the absorbed energy would be five orders of magnitude below the heat produced by the normal human metabolism (about 100 W).

However, this does assume free space propagation and free space impedance. No big deal as long as you don't expect better than ball park values for any actual risk. RF hazard is a very approximate business.

 

[Drakkith]

The primary concern is that my son's room is located there, and I want to determine if it is affected by the signal.

Despite decades of study, there is little-to-no good evidence that cell phone and other electromagnetic signals are harmful at the low intensities that are used in communication. Unless the military is pointing a high-power radar system at your house from point-blank range you are better off worrying about known health risks, not imaginary ones.

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