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UER Forum > Archived UE Tutorials, Lessons, and Useful Info > Just how dangerous are microwave antennas? (Viewed 785 times)

Mark Very Noble Donor Location: South Carolina Gender: Male What is a lion, king of the savannah, when hes at the south pole? \|	Just how dangerous are microwave antennas? < on 10/18/2005 12:45 PM >

	Just how dangerous are microwave antennas? Please no assumptions. Documentation or some experience is requested. I would like to know if climbing by will fry my balls, or is it prolonged exposure. Also how close is to close? Thanks. "If the threat level goes up its probably because of me." "I am looking for a girl who enjoys headbutting beltbuckles"

atomx Location: Brighton, ON Gender: Male \| \|	Re: Just how dangerous are microwave antennas? <Reply # 1 on 10/18/2005 12:49 PM >

	Just don't spend too much time behind, or beside them. More than likely you won't be able to get infront of them, that's not a good idea. Really not a good idea. I'll get the stats for you later. Oh, and several meters is close. [last edit 10/18/2005 12:50 PM by atomx - edited 1 times] "Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning." - Richard Cook

Spyder Location: Ottawa Gender: Male Holy Fuck!!! There's a tree frog in the toilet! \|	Re: Just how dangerous are microwave antennas? <Reply # 2 on 10/18/2005 2:07 PM >

	From Andrew's Antenna a leading manufacturer of Microwave Antennas Radio Frequency Exposure Levels Near Terrestrial Microwave Antennas Robert Gunnels, Senior Research Engineer Questions frequently arise about the safety of personnel exposed to radio frequency radiation while working in close proximity to point-to-point microwave antennas. There is an approximate method for determining the maximum power density in front of a typical prime-focus parabolic reflector antenna for a given antenna size and power input. This approximation is also valid for dual reflector antennas that are sometimes used in such applications. For most prime-focus symmetrical reflector antennas used in point-to-point microwave communications, the feed horn is designed with a gain of approximately 10 dBi and is aligned, with its phase center at the focal point, so that its direction of maximum gain is toward the center of the reflector. Since the feed horn aperture is relatively small, it can be considered as a point source at its phase center. Thus, energy radiates from it with a spherical phase front, resulting in a decrease in power density according to the inverse square law with respect to distance. Because the direction of maximum feed gain is toward, and the distance from the feed aperture to the reflector is a minimum at, a point in the center of the reflector, then the highest power density will be incident at this point on the reflector surface. With a gain of 10 dBi, the feed's EIRP (effective isotropic radiated power) in the direction toward the reflector center will be, neglecting losses in the feed, 10 times the input power to the antenna. Then, by considering the surface area of a sphere with a radius equal to the distance between feed aperture and reflector center, the power density at this point can be calculated. Antennas of this type usually have F/D (focal length to diameter ratio) values from 0.25 to about 0.4, with typical designs using a ratio of approximately 0.35. Thus, by knowing the antenna diameter, we can estimate the focal length and calculate the surface area of a sphere with that radius. Since F/D = 0.35, then F = 0.35D, and the surface area of a sphere with its radius equal to that focal length would be 4pr2 = 4p(0.35D)2 = 1.54D2 then, the power density (P) at the reflector center would be P = EIRP / 1.54D2. As an example, consider a 1 foot (30.48 cm) diameter antenna with 1 watt input power: P = 10 (1 watt) / 1.54(30.48)2 = 7 mW / cm2 . Since the energy reflected from the parabolic reflector's surface has a substantially planar phase front, then the maximum power density of 7 mW / cm2 will be present in the center region and just in front of the antenna aperture. This level will generally decrease in all other directions at the same distance from the antenna. In the case of shielded high performance antennas, power densities in locations other than immediately in front of the antenna's aperture (such as beside or behind the antenna) will be many orders of magnitude below this level and will decrease approximately by the inverse square law with distance. It is important to realize that for the same antenna power input, the power densities present in the aperture of larger antennas decrease dramatically compared with those of smaller sizes. This is because the same power is now being distributed over a larger area, which increases as the square of the aperture's radius. As an example, for an 8 foot (243.8 cm) diameter antenna with 1 watt input as above, the power density at the aperture center would be approximately P = 10 (1 watt) / 1.54(243.8)2 = 0.11 mW / cm2. In most applications today, including those using small (i.e., 1 foot diameter) higher frequency microwave antennas, power inputs are generally well below the 1 watt level used in the example above and, therefore, actual power densities are proportionately lower. With a safety limit set by the American National Standards Institute and OSHA of 10 mW / cm2 (averaged over a 6-minute period) worst case exposure levels, even immediately in front of typical operational point-to-point microwave communications antennas, will generally be well below those indicated in these standards. The possibility of disrupting radio communications would probably be the greater danger in having personnel in front of, thus blocking, the antenna aperture.

cpkangaroo Location: Longmont, CO Gender: Male \| \|	Re: Just how dangerous are microwave antennas? <Reply # 3 on 10/18/2005 2:21 PM >

	Echoing what Atomx said, you'll be fine as long as you keep moving. As long as it was for a very brief amount of time (a couple of seconds or so to jog through a lobe), I would personally feel comfortable at any distance, although I certainly wouldn't ever touch the damn thing. Here's some good info on RF Safety from: - The FCC http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet56/oet56e4.pdf - Some hand-holding pansies (OSHA) http://www.osha.gov/SLTC/radiofrequencyradiation/index.html - And the ARRL (I'm not only a lurker, I'm also a member) http://www.arrl.org/news/rfsafety/hbkrf.pdf Buy heroin, it's good!

Mark Very Noble Donor Location: South Carolina Gender: Male What is a lion, king of the savannah, when hes at the south pole? \|	Re: Just how dangerous are microwave antennas? <Reply # 4 on 10/18/2005 4:54 PM >

	Thanks guys. "If the threat level goes up its probably because of me." "I am looking for a girl who enjoys headbutting beltbuckles"

Ninjalocksmurf Gender: Male \| \|	Re: Just how dangerous are microwave antennas? <Reply # 5 on 10/20/2005 6:18 PM >

	There's no lack of in depth information in this thread, although I don't know what most of it means. Maybe this will help, maybe it won't. About 20 years ago, I watched a guy hold an uncoooked hot dog between the "head" and the "dish" of a military microwave unit while somebody else hit the transmit button for 10 seconds and it didn't just cook the hot dog, it cooked it so much that it split and bubbled and looked too nasty to even think about eating. Personally, all the deep scientific data aside, I'm staying way the hell away from them. Do as you see fit.

Dusty Location: Toronto Gender: Male \|	Re: Just how dangerous are microwave antennas? <Reply # 6 on 10/21/2005 4:14 AM >

	That was a long-winded way of saying that microwave transmitters don't put out much power. But I heard bad stories too - that you'll be cooked if you pass in front of a microwave horn. On the other hand, Spyder's post says that they put out about 1 Watt, which is basically negligible. Good luck cooking a hot dog in a 1 Watt microwave... CPKangaroo's info has to do with RF, which is a bit more general than just microwaves, and there are basically no known short term effects of RF (radiofrequency) transmitters outside the microwave frequencies. (Unless you have your own MRI and you are overclocking it) So I think more information is needed - are there (or were there) high-power microwave transmitters?

cpkangaroo

Location: Longmont, CO
Gender: Male

Re: Just how dangerous are microwave antennas?
<Reply # 7 on 10/21/2005 1:28 PM >

Posted by Dusty
So I think more information is needed - are there (or were there) high-power microwave transmitters?

I'm sure they exist, but it wouldn't make any sense for them to be used in any real-world application. One would increase the power on a transmitter to allow the signal to more easily propagate through obstructions. Microwaves have such a small wavelength that they're very easily blocked, so they are very close to a true line of sight communications medium. Therefore, it wouldn't make much sense to increase the power too much since they're only going to be used in environments with very few (or no) obstructions.

As far as the hot dog is concerned, realise it was being held very close to the focal point of the dish, the point with the highest concentration of energy. Also remember, your body has a lot more mass than a hot dog, so even if you stick your face right in the middle of that dish, it will take more than a few seconds to heat up your head enough to pop out your eyes.

Buy heroin, it's good!

DriverDan Location: Austin, TX Gender: Male \| \| \|	Re: Just how dangerous are microwave antennas? <Reply # 8 on 10/21/2005 5:29 PM >

	The key thing to remember is that signal strength follows the inverse square law. Intensity decreases exponentially the further away you get. So 2 feet away is significantly better than 1ft away, etc.

roofwalker Gender: Male \|	Re: Just how dangerous are microwave antennas? <Reply # 9 on 10/23/2005 3:38 PM >

	I personally try to stay as far away from these as possible. If you get a warm feeling in your head while passing through the beam, that's never a good sign.

Spyder Location: Ottawa Gender: Male Holy Fuck!!! There's a tree frog in the toilet! \|	Re: Just how dangerous are microwave antennas? <Reply # 10 on 10/24/2005 1:48 PM >

	Also remember that the microwave dish is designed to reflect most of the energy forward, if you are behind the dish there is very little energy, even if it were a high power transmitter. The towers to avoid are the AM, FM, and other non dish type of towers, they usually radiate in all directions and use many kilowatts of power.

Logan Location: Ra-Cha-Cha, NY Gender: Male We miss you Jerry \| \| \|	Re: Just how dangerous are microwave antennas? <Reply # 11 on 10/24/2005 5:17 PM >

	Its the radiation that gives you the cancer. Dont put cats in microwaves. Cogito Ergo Sum

Mickael

Moderator

Location: Canada
Gender: Male

Re: Just how dangerous are microwave antennas?
<Reply # 12 on 10/24/2005 5:34 PM >

Posted by Logan
Its the radiation that gives you the cancer. Dont put cats in microwaves.

Not THAT type of radiation (microwaves are non-ionizing radiation)

By the way, that was (beside Masher's posts)the most useless post ever.


Non-ionising radiation has enough energy to move things around inside a cell 
but not enough to change cells chemically.  The radiation from a microwave 
oven is non-ionising.  Other examples include
 
    * Ultraviolet rays from the sun or sunbeds    
    * Electromagnetic fields    
    * Radio waves    
    * Radiation waves given off from household electrical appliances, heaters, 
        mobile phones with or without headsets and computers and their screens
 
The only type of non-ionising radiation that we know can cause cancer is over exposure 
to ultraviolet rays, which causes skin cancer. 
 
http://www.cancerhelp.org.uk/help/default.asp?page=8774

Need forum-related help / Besoin d'aide reliée au forum ? Contact a moderator

Logan Location: Ra-Cha-Cha, NY Gender: Male We miss you Jerry \| \| \|	Re: Just how dangerous are microwave antennas? <Reply # 13 on 10/25/2005 6:04 AM >

	hmm, I retract my previous statement. Sorry. What do they teach in those college courses these days anyway? Cogito Ergo Sum

roofwalker

Gender: Male

Re: Just how dangerous are microwave antennas?
<Reply # 14 on 10/25/2005 6:42 AM >

Posted by Spyder
Also remember that the microwave dish is designed to reflect most of the energy forward, if you are behind the dish there is very little energy, even if it were a high power transmitter. The towers to avoid are the AM, FM, and other non dish type of towers, they usually radiate in all directions and use many kilowatts of power.

Although, as ArmchairExplorer pointed out in another thread, the sidelobes from a directional dish can still be pretty powerful from the sides and behind. .
[last edit 10/25/2005 6:43 AM by roofwalker - edited 1 times]

RobA Location: Ontario Gender: Male \|	Re: Just how dangerous are microwave antennas? <Reply # 15 on 10/31/2005 8:24 PM >

	An anecdote: The father of a friend worked for ON-Tel (long since retired). He claims that after doing maintenance on microwave horns they would "quickly" verify they were transmitting again by sticking their heads in front with eyes closed. If the horn was on, they would see "sparks" and "flashes". He admits now it was stupid as they were probably cooking their brains...

Dusty Location: Toronto Gender: Male \|	Re: Just how dangerous are microwave antennas? <Reply # 16 on 11/1/2005 1:17 AM >

	I keep hoping that someone who is qualified to give an opinion will pipe up here. I can see that at least some of the information in this thread is incorrect and that gives me reason to doubt the rest of it. In the meantime, I'd like to clarify to the best of my understanding: A 1 watt dish is not remotely dangerous, no matter how close you get to it. Cellphones have 1/4 watt transmit, don't they? I can see lots of good reasons why a dish would transmit at higher power, though. Engineers are power mad, for one. If a dish is focused, then its intensity does not drop off according to the inverse square of distance. As I understand it, microwaves have the same effect on the human body as they do on a microwave dinner: they heat it up. The danger arises because they penetrate some distance into the object or body and, as a result, heat it from the inside. So it can heat up your internal organs before the heat travels outward to where your skin can sense it. And your internal organs are just fine the way they are, thank you very much. So theoretically, a high-power dish might cook your innards before you felt hot. Any peripheral never stimulation (where muscle twitches, pain, or flashes and <shudder> sparks) are a sign of high RF power and, although they might not do you any damage, you should go play somewhere else.

rostit

Location: South Eastern PA
Gender: Male

Imma herpin ma derp like YEAHH!!

Re: Just how dangerous are microwave antennas?
<Reply # 17 on 11/1/2005 1:56 AM >

A 1 watt dish is not remotely dangerous, no matter how close you get to it. Cellphones have 1/4 watt transmit, don't they? I can see lots of good reasons why a dish would transmit at higher power, though. Engineers are power mad, for one.

If a dish is focused, then its intensity does not drop off according to the inverse square of distance.

You are correct in the way that the energy is focused. However, if you are not in the direct live of transmission then you are in with the inverse square law of energy dissapation. For you to be directly in front of most MR feeds would mean that you are on the outside of the tower, without a platform under you and then you would be falling. There is almost never a platform in front of MR since it will cause too much of the power to be absorbed along with other issues. You will almost always have the catwalk on the back side of the dish with the dishes being pivotable for service. You are safe as long as you are behind the MR dish.

Engineers are not power hungry, the are efficiency hungry, more for less. They also need to design the transmitters and to design a power supply for a low power MR transmitter is much better than a high power transmitter.

As I understand it, microwaves have the same effect on the human body as they do on a microwave dinner: they heat it up. The danger arises because they penetrate some distance into the object or body and, as a result, heat it from the inside. So it can heat up your internal organs before the heat travels outward to where your skin can sense it. And your internal organs are just fine the way they are, thank you very much. So theoretically, a high-power dish might cook your innards before you felt hot.

True statement again, just wrong context. An average MR oven in your kitchen runs from 700-1200watts at 2.4ghz. The average power of a commercial MR transmitter seems to vary, but in the average of 15-50 watts. You also need to remember that at higher frequencies they run lower power. Because they are running a digital signal the amount of interference isnt as much of a problem.

What you need to watch out for is the lower frequency antenna's. RF is much more dangerous than than MR. A local radio station will run at 50KW. Thats 1000 times more than the average MR transmitter.
Here's a few simple but effective tools to check your level of exposure and to make absolutely sure you dont get fried.

1. Neon Indicator Bulb. usually has two little probe like things inside the bulb with no filament. They will actually glow if you are near an RF source that is putting out more than 60-80watts of power(modulated/continuous power).

2. Microwave leakage indicator (MCMelctronics.com) sold for testing microwave ovens for leakage around the doors and the case. Pretty cheap if I recall.

3. AM/FM radio, it will braodcast whatever is coming out if its strong enough no matter what you are tuned to. If you ever ran a CB radio near your clock radio with the radio on, you know what I mean.

4. CCFL out of a laptop screen or the "neon" lights that ricers put in their PC cases to illuminate them. Just like the Neon bulb above. Nothing to wire either of them to. Just holding them in a strong enough RF feild will excite the gas inside as cause it to glow. I have a Neon Bulb inside a film container with a hole in the lid, so I can see it glow easier. I used it for testing homebrew highgain antenna's.

One way to protect yourself is to obtain an ESD jacket from a uniform company. They are used by people who work with static sensitive electronics. They are about 30-40bucks(US) and they have metal thread woven through them. You can attach a static strap lead like used on a computer repair and then conect the other end to the structure you are on. Then the area around you is grounded and it will keep you from being a viable portion of the antenna and drain any rf away from you. Its not foolproof since your head is exposed but it will help alot. Plus they are stylish.

I hope this helps you a bit. Basically, stay off of Radio and TV transmitter antenna'a. CellPhone and MR repeater antenna's are relatively safe. The MR to watch out for is Radar MR, like at NRL in MD when it was operational. Plus any operational Atlas, Nike Radar. Those are the Highpower Mr transmitters that people cook hotdogs, popcorn, candybars, and cats on. If you make it past the Mp's and climb up onto the dome then I guess you deserve what you get. Commercial MR Transmitters are pretty safe though.

/I even connected a magnetron tube from a microwave outside of the oven on my bench and it didnt do anything. i put my hand in front of it and even left it on to see what type of damage it could be used for. The best i found was jamming WiFi. Without the wave guide it was harmless besides the HV powering it.

Be safe!

UER Forum > Archived UE Tutorials, Lessons, and Useful Info > Just how dangerous are microwave antennas? (Viewed 785 times)

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