How safe is a digital-TV repeater?

[logics]

I've read safe RF radiation for human in sleep should be below 1\muW/m² and 0.1 for digital pulsating radiation. Is that true?

If the station on a roof has power: 30W
- at what distance radiation is below 0.1 microwatt through a thin wall or at sight?
- through how many storeys can it go?
- is there an effective way to screen it?
Thanks

 

[russ_watters]

Where did you read that?

 

[jtbell]

You have to take into account the radiation pattern of the antenna. Most TV broadcast antennas concentrate the radiation near the horizontal plane so that they don't send a lot of energy uselessly into outer space or straight down to the ground underneath. At least this is true for full-power TV transmitters in the US; low-power repeaters (or "translators" as we call them here) might be more isotropic, but I don't know anything about actual practice.

As a starting point, you can calculate the average intensity at distance r as $P/4 \pi r^2$, but it will probably be greater in the horizontal plane, and less in the vertical direction; and it will be further reduced by building materials.

In general, wood blocks TV/radio signals the least, stone and brick block them more, and metal foil (e.g. some types of inside-wall insulation) or metal mesh (e.g. stucco walls) or plates (metal roofs) block them a lot. I would guess that wood walls might reduce the strength by a factor of 10, stone/brick by 100, metal by 1000 or more.

Also, I wouldn't think of digital TV signals as "pulsating." The binary data is not represented as a simple on-off switching of the signal, but instead as a complicated phase modulation. In the US, most digital TV transmitters actually emit less power than the analog transmitters that they replaced a few years ago, because the digital encoding allows good reception with a lower signal strength at the receiving antenna.

 

[logics]

Most TV broadcast antennas concentrate the radiation near the horizontal plane so ...

... the station is about 100 meter from my window more or less on the horizontal plane (maybe a few yards above), can you find out the field strength?
Does that kind of RF pass through a wall?

 

[jtbell]

Does that kind of RF pass through a wall?

It has to be able to go through walls, at least partially, so people can use indoor TV antennas.

(I added some more stuff to my preceding post while you were posting yours.)

 

[logics]

. I would guess that wood walls might reduce the strength by a factor of 10, stone/brick by 100, .

It has to be able to go through walls, at least partially, so people can use indoor TV antennas. :smile

The walls are not stone nor bricks, but flimsy porous calcareous material, then put in a large window, can you make a rough general estimate if I get more than 1 microwatt, altogether (if it is not pulsating) ?
Thanks a lot, jitbell
Isn't it advisable to do some kind of screening, anyway? how, aluminim Venetian blinds, or what?

 

[jtbell]

flimsy porous calcareous material

Are you sure there's no metal inside the walls? In the western USA, "stucco" construction is rather common, in which the walls are basically plastered over a wire mesh (like what we call "chicken wire") with some wood or metal support posts. People who live in such houses usually find it very difficult to get good TV reception with an indoor antenna, and have to mount an antenna outdoors on the roof.

As for the window, metal blinds would block the signal a lot, even if they're thin strips that let a lot of light through. Also, glass with very thin metal coatings for energy efficiency (what we call "low-E" windows) often also block a lot of RF.

 

[logics]

Are you sure there's no metal inside the walls?

I'm sure, here only the pilasters on the 4 corners are ferro-concrete and in between just blocks of porous calcareous material.
Can you now give me your verdict, can I (and the children) survive , or should we move?

If I had to use chicken wire, what is the most effective size to block those frequencies?

 

[DragonPetter]

Why are you concerned about this radiation in the broadcast spectrum? I don't think there are any known safety issues with UHF radiation, and I think this has been studied extensively. It is non-ionizing radiation, and I doubt your body is a very good antenna for absorbing this energy.

Are you concerned about electronics being disrupted by the radiation?

Your cell phone next to your head might be giving more radiation to your body than this antenna.

 

[skeptic2]

http://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/oet65.pdf

 

[logics]

Your cell phone next to your head might be giving more radiation to your body than this antenna.

Sure, but only for a few minutes, not 24h/day. The article I read said that expecially when asleep field strength should be lower than 1, for adults!
Can you work out the field strength, with those parameters?, thanks

 

[DragonPetter]

Sure, but only for a few minutes, not 24h/day. The article I read said that expecially when asleep field strength should be lower than 1, for adults!
Can you work out the field strength, with those parameters?, thanks

What damage do you think it could be doing to your body? Dielectric heating like a microwave?

Can you link the article?

 

[logics]

The article was in a newspaper, but I found same values http://www.safelivingtechnologies.ca/EMF_Safety_tips.htm

 

[DragonPetter]

The article was in a newspaper, but I found same values http://www.safelivingtechnologies.ca/EMF_Safety_tips.htm

That company is probably designing a tinfoil helmet too, because people will buy it. That same company says EM radiation causes:

"Neurological: headaches, dizziness, nausea, difficulty concentrating, memory loss, irritability,

depression, anxiety, insomnia, fatigue, weakness, tremors, muscle spasms, numbness, tingling,

altered reflexes, muscle and joint paint, leg/foot pain, “Flu-like” symptoms, fever. More severe

reactions can include seizures, paralysis, psychosis and stroke.

Cardiac: palpitations, arrhythmias, pain or pressure in the chest, low or high blood pressure,

slow or fast heart rate, shortness of breath.

Respiratory: sinusitis, bronchitis, pneumonia, asthma.

Dermatological: skin rash, itching, burning, facial flushing.

Ophthalmologic: pain or burning in the eyes, pressure in/behind the eyes, deteriorating vision,

floaters, cataracts.

Others: digestive problems, abdominal pain, enlarged thyroid, testicular/ovarian pain, dryness of

lips, tongue, mouth, eyes, great thirst, dehydration, nosebleeds, internal bleeding, altered sugar

metabolism, immune abnormalities, redistribution of metals within the body, hair loss, pain in the

teeth, deteriorating fillings, impaired sense of smell, ringing in the ears."

 

[logics]

Bau Biologie makes no helmets, I suppose, but can you help me at all?
What is RFM?
What is the optimal size of a chicken-wire mesh?
You'll oblige me

 

[xxChrisxx]

Better get one of these too.
http://en.wikipedia.org/wiki/Tin_foil_hatDAMN! Beaten to it. Spent too long reading that site.

 

[DragonPetter]

Bau Biologie makes no helmets, I suppose, but can you help me at all?
What is RFM?
What is the optimal size of a chicken-wire mesh?
You'll oblige me

I'm not trying to mock you because I am not an expert in this, but I see demotivation in obliging you with time consuming calculations when I see what my efforts would be for, besides learning something myself.

As far as a wire mesh, you want the spacing in your wires to be a certain fraction less than the wavelength of the radiation you're trying to block.

 

[logics]

I'm not trying to mock you because I am not .

I do not know if you have children [around]. But I am not saying I believe anything, I only would like to know, roughly, what field strength might be. I'll decide whether to worry only afterwards.

 

[xxChrisxx]

Seriously OP. Ask yourself this.

Why does it matter what the level is where you sleep?
Why are you more vulnerable when you are asleep?

 

[DragonPetter]

I do not know if you have children [around]. But I am not saying I believe anything, I only would like to know, roughly, what field strength might be. I'll decide whether to worry only afterwards.

I'm too young to have children yet. I think a good idea would be to call the owner of the transmitting station and ask them what safety hazards you are susceptible to by living where you are, and what documentation they have of standards and procedures used when they established the station. Perhaps you could call a local public administration office and tell them your concerns? I don't think building an anechoic chamber house is very practical or necessary.

 

[xxChrisxx]

I've got to post this before the thread gets locked.

As there is no proper evidence for a link between the low level EMF or RF and really any adverse effects. The site you linked to is a crackpot site, that is breeding fear to sell you the cure to the disorder you don't have.

The following is not a flippant remark, but your should seriously consider:
Hypochondria
Psychosomatic Illness.

Both are more harmful than that transmitter.

 

[DragonPetter]

Seriously OP. Ask yourself this.

Why does it matter what the level is where you sleep?
Why are you more vulnerable when you are asleep?

I would guess the idea is that during sleep your brain does a lot of organization and processing of information and memories. Also, your body performs a lot of maintenance functions during sleep. They probably think that EM waves disrupt these processes.

 

[Drakkith]

I do not know if you have children [around]. But I am not saying I believe anything, I only would like to know, roughly, what field strength might be. I'll decide whether to worry only afterwards.

It's pretty obvious that you have already decided that it is unsafe, otherwise you wouldn't be here asking this question. The fact is that small amounts of this type of EMR have never been scientifically shown to have ANY effect, positive or negative, to people nearby.

Anyways, a quick rough calculation gave me about 2 microwatts using the formula here: http://en.wikipedia.org/wiki/Inverse-square_law#Example

 

[Bobbywhy]

Here is a website that appears to be legitimate (not a crackpot outfit more interested in selling products) that gives information on potential health effects:

“Biological Effects
There are two undisputed health effects that can occur with exposure to high levels of RF energy:
Heating of the human body
Electrostimulation (RF shocks and burns)

Although some researchers believe that exposure to low-level fields for long periods of time can result in other harmful effects, none of these nonthermal effects are the basis of any of the major standards in the world. And while research and the debate continues over low-level effects, body heating and shocks and burns have never been disputed.

RF radiation is almost exclusively an occupational problem. It is rare for someone to be exposed to significant RF field levels outside of work. There is one major exception. The proliferation of wireless antennas on rooftops has made public exposure and exposure to workers outside the electronics industry a concern for anyone that goes on a rooftop.”
http://www.rfsafetysolutions.com/RF%20Radiation%20Pages/Biological_Effects.html

Once you decide to investigate the radiation in your home you must measure it. Here are some US Federal Standards with recommendations:

“Occupational Safety and Health Administration
Health Effects
Electric and magnetic fields are complex physical agents whose potential health effects are the subject of much research. Particularly controversial are the biophysical mechanisms by which these RF fields may affect biological systems. General health effects reviews explore possible carcinogenic, reproductive and neurological effects. Health effects by exposure source are noted in radar traffic devices, wireless communications with cellular phones, radio transmission, and magnetic resonance imaging (MRI).”
http://www.osha.gov/SLTC/radiofrequencyradiation/

These may help you decide what’s best for you and your family.

 

[logics]

It's pretty obvious that you have already decided that it is unsafe, otherwise you wouldn't be here asking this question.

If I had decided, I wouldn't ask anyone, just move, I suppose 1 Km (= 0.02) would be safe. Of course, I was joking before , with jitbell

I did not even read the link I quoted, so I do not know what some of you are talking about. I quoted the first link I found in a Google-search: "Bau Biologie exposure standars", my only intent was to quote the standards I read in the article, (you can check , that's the first to pop up), are you so competent to disprove Bau standards?

I wrote here just to get a vague idea about what the value (you say 2 ?) of field strength might be, as I am not sure: if /4π applies when a beam is highly directional, ...what is the absorption of a wall ,... what is the wavelenght of TV repeaters and so on...I expected this kind [of] replies,

It's better be safe than sorry, I suppose (remember the thalidomide tragedy?), I am quite ancient, any way ready to go, not much worried about myself. Recently there has been an alert by WHO for cellphones etc. (you can find many videos on youtube (ELECTROSMOG21,EMFWATCH etc).

But that is not the problem, this is a physics subforum, I asked only for scientific data. Thank you.

 

[Vanadium 50]

Locked pending moderation.