harmful Radio waves ... suddenly no one talk about it  - Page 1
Forum section: electronics / general

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: January 09, 2016, 05:20:11 pm
content: After everyone is talking and making something connected to this and connected to that, lamp , door bell , baby monitor , connected bed to check if you sleep well, am waiting for the connected toilet seat to check if your poop is OK. anyway that's not the question, that just me. The point is some years ago, everyone is talking about the potentiel harm that maybe caused to brain cell by electromagnetic waves BUT how everyone is OK now with a home basically with multiple source of EMW.Note : the question here is not if they are harmful or not, more ppl clearly have brain damage now than beforebut still not proved to be related to those gadget as i know, the question is more about consumer behavior.

author: amyk
author_rank: Super Contributor
timestamp: January 09, 2016, 06:16:28 pm
content: There's still a minority, which is why those snake-oil "electromagnetic blanket" sellers are still around, but I think most people have finally realised that low-power RF is not going to hurt them.

author: calexanian
author_rank: Super Contributor
timestamp: January 09, 2016, 07:53:54 pm
content: Snake oil get few repeat customers.

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 09, 2016, 08:37:26 pm
content: "Harmful radio waves" .... suddenly we have discovered that there is nothing to talk about.

author: tggzzz
author_rank: Super Contributor
timestamp: January 09, 2016, 08:49:00 pm
content: There is an easy answer to this question. It is simply that modern tinfoil hats are much more effective than the first generation tinfoil hats.In addition, modern hearing aids are no longer susceptible. I once made myself rather unpopular at work by demonstration how RF radiation could plausibly seriously harm infants...Grandparent is holding their newborn grandchild. Child is dropped onto the floor when someone's walks past. Why? Grandparent has deafaids, and when someone with an 1800MHz cellphone walks past they are startled by a sudden very loud noise in their ear - and the startle reflex causes them to drop the child.

author: Brumby
author_rank: Unknown
timestamp: January 10, 2016, 12:15:39 am
content: Quote from: amyk on January 09, 2016, 06:16:28 pmI certainly don't run screaming at the thought of RF fields - but I would have concerns about standing next to the radiating element of a 100kW radio transmitter or the pulsed beam of a high powered radar.My question is: When considering safety in EM fields - what is the threshold?

author: JimRemington
author_rank: Regular Contributor
timestamp: January 10, 2016, 12:45:41 am
content: My wife's dad was in the Navy around 1945, and he described how he and other sailors would sometimes stand in front of the radar dishes to warm up.He deeply regretted that he never thought of inventing the microwave oven

author: Syntax_Error
author_rank: Regular Contributor
timestamp: January 10, 2016, 01:43:29 am
content: Quote from: Brumby on January 10, 2016, 12:15:39 amSearch for maximum permissible exposure and specific absorption rate. These topics give a good introduction to RF exposure limits and how it relates to field strength and frequency, and the variables that go into determining those two derived variables. Very interesting reading. The TLDR version is that RF and microwaves are nonionizing radiation, so exposure risk comes down to energy absorption and heating value. Since different frequencies are absorbed to different degrees by the human body, there is no one singular limit; it varies with frequency. Also, duty cycle during an operating period and average power during transmission determine average field strength and dosage over time (along with distance and shielding).It may seem complicated, but the good news is that RF safety is taken quite seriously by governmental types, and laws are in place that require standoffs such as fencing and signs to ensure public safety from powerful transmitters. Your mobile phone or WIFI router pose no dangers to you, nor does your microwave oven as long as you don't defeat its safety features.

author: ADC-1995
author_rank: Regular Contributor
timestamp: January 10, 2016, 05:06:45 am
content: https://www.osha.gov/SLTC/radiofrequencyradiation/healtheffects.html

author: miguelvp
author_rank: Super Contributor
timestamp: January 10, 2016, 05:35:43 am
content: When my dad was on the U.S. air force as a technician stationed in Spain, they used to light up fluorescent lights below the radar transmitters to impress the girls. I guess my mom being one of those.Very stupid, yes, but at least not harmful enough for me to be conceived afterwards and after over 50 years I think I didn't have any adverse effects from the radiation.I think the genetically engineered crops we eat often now a days are way more harmful. But that's just a feeling more than reality.Good form/color but bad nutrition/taste.Still, I wouldn't want to live near a big power line.

author: Seekonk
author_rank: Super Contributor
timestamp: January 10, 2016, 08:01:36 am
content: Energy should always be respected. Tower technicians are required to wear energy monitors. There are studies that bees die near cell phone towers. There is a rise in breast cancer among women that stick a cell phone in their bra. The responses show an ignorance of energy. I knew a guy that used to wash his hands in used PCB transformer oil. He said it was the best degreaser ever. That doesn't mean you should do it.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: January 10, 2016, 09:19:42 am
content: Quote from: Seekonk on January 10, 2016, 08:01:36 amNo there aren't. The one 2009 Swiss study that woo salesmen claim showed that showed they reacted to ringing phones next to the hive by getting pissed off. There was no connection shown beyond that, and nothing to show any harm beyond bees finding them as annoying as many people do.QuoteNo there isn't. It's an urban myth. One woman who got breast cancer unfortunately young carrying her phone in her bra and (probably understandably) needed to blame something so blamed that isn't a rise in breast cancer amongst women that stick a phone in their bras. No studies have corroborated that claim but yet a cancer victims desperate grasping at straws still made international news with her claim presented as irrefutable fact. More women are getting breast cancer full stop, where they keep their phones seems to have no effect on that.

author: tggzzz
author_rank: Super Contributor
timestamp: January 10, 2016, 09:58:58 am
content: Quote from: Seekonk on January 10, 2016, 08:01:36 amYes. So should science.QuoteCorrelation (if there is any) is not causation. After all bigger shoe size => better spelling ability.QuoteReference please. Ensure it contains sufficient information that we can assess its validity.Anecdotes will be ignored.

author: German_EE
author_rank: Super Contributor
timestamp: January 10, 2016, 11:17:59 am
content: All the information you need, your tax dollars at work.http://www.fcc.gov/oet/rfsafety/rf-faqs.htmlhttp://www.fcc.gov/encyclopedia/radio-frequency-safetyhttp://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet56/oet56e4.pdf

author: VK5RC
author_rank: Unknown
timestamp: January 10, 2016, 11:35:02 am
content: Re Bra phone transport and breast cancer, clearly there will be an association, as the woman is frequently doing breast self examination! There was, for a brief period of time, an association (NOT causal ) with breast trauma and cancer from precisely the same issue.Causality is best determined by1. Randomised Intervention study, preferably double blind, NOT a cross sectional study.2. Demonstration of a dose response curve/associationHigh power RF is good at cooking things, intended or not. My homebrew EME 1296MHz transmitter puts out about 400W, I am careful but not paranoid.

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: January 10, 2016, 12:25:13 pm
content: Quote from: Brumby on January 10, 2016, 12:15:39 amgood question , and how much appliance connected at the same time in order to not hit that limit.But still i think most ppl now accept the risk of RF waves in order to get that extra bit of confort. it's like the car or a plane, everyone accept the risk of accident or crash in order to get that confort.

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: January 10, 2016, 12:40:25 pm
content: Quote from: Seekonk on January 10, 2016, 08:01:36 amthose study as old as the cell phone it self, still the coincidence of two phenomena doesn't mean a cause-effect relation.

author: Seekonk
author_rank: Super Contributor
timestamp: January 10, 2016, 04:18:25 pm
content: No, it doesn't. I grew plants with ultrasonic sound. Certainly a half watt couldn't do anything, but it did cause major changes. Are you saying the suns radiation doesn't cause some cancers? Millions and millions of cells reproduce. Only an unimaginably small percentage have errors. Chemicals and energy change these statistics and it doesn't take much. In the end we are all a statistic. The government has set limits for radiation. Let's face it, many people would rather die than be without their cell phone. Mankind doesn't have to worry about Terminators in the future. We have met the enemy and it is us. It isn't even sport to continue this conversation with you.

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: January 10, 2016, 04:59:47 pm
content: Quote from: Seekonk on January 10, 2016, 04:18:25 pmi can agree on that

author: Seekonk
author_rank: Super Contributor
timestamp: January 10, 2016, 10:18:49 pm
content: Being out of the current news cycle doesn't mean that the science is in on radiation.

author: MrSlack
author_rank: Frequent Contributor
timestamp: January 11, 2016, 08:48:00 am
content: I used to work inside a large metal box with microwave radar equipment. As did many people I worked with and they'd been in there for 40+ years. We're all still here.A couple of guys accidentally left a body part in front of a waveguide/funnel and ended up with a neat toasted square on themselves and a nice bacon smell but that was about it. That heals up nicely after a couple of weeks.YMMV but meh.Shit that scares me is big lathes. One slip up and your torso is gone in 2 seconds flat.

author: VK5RC
author_rank: Unknown
timestamp: January 11, 2016, 09:11:29 am
content: @MrSlack, agree+++ that and the power take off on a tractor, the irresistible force.

author: MrSlack
author_rank: Frequent Contributor
timestamp: January 11, 2016, 09:39:06 am
content: Definitely. I grew up in the sticks on farms. In the Deere manuals there's this graphic that always made me laugh about that:

author: Richard Head
author_rank: Frequent Contributor
timestamp: January 11, 2016, 09:49:41 am
content: There is a rise in breast cancer among women that stick a cell phone in their bra.Hmm. I wonder if the rise in cervical cancer is related?

author: tszaboo
author_rank: Super Contributor
timestamp: January 11, 2016, 10:22:14 am
content: Quote from: hamdi.tn on January 09, 2016, 05:20:11 pmMe too, it is surprising, how many illness can be detected just by analyzing poo and wee.But think about the implications of smart connected devices. They work from batteries, and they dont need to be recharged every day, like phones. They have like a CR2032 and work years from it, or maybe AA and half a year.Your laptop or phone will generate orders of magnitude more RF.So, i'm not worried.

author: ADC-1995
author_rank: Regular Contributor
timestamp: January 12, 2016, 04:54:57 am
content: I think defining what is damaging and what is not is the key. The World Health Organization has a good overview and defines each type of radiation. Below are all taken from the site and sums it up. So “yes” and “no” for the potential effects of RF on tissue. Is it ionizing or non-ionizing, but don't stand in front of a gigawatt antenna and think it will not harm you.Ionizing radiation (harmful)Ionizing radiation is radiation with enough energy so that during an interaction with an atom, it can remove tightly bound electrons from the orbit of an atom, causing the atom to become charged or ionized.Here we are concerned with only one type of radiation, ionizing radiation, which occurs in two forms - waves or particles.Forms of electromagnetic radiation. These differ only in frequency and wave length.Heat wavesRadio wavesInfrared lightVisible lightUltraviolet lightX raysGamma raysLonger wave length, lower frequency waves (heat and radio) have less energy than shorter wave length, higher frequency waves (X and gamma rays). Not all electromagnetic (EM) radiation is ionizing. Only the high frequency portion of the electromagnetic spectrum which includes X rays and gamma rays is ionizing.http://www.who.int/topics/radiation_non_ionizing/en/Non-ionizing (non harmful)Non-ionizing radiation is the term given to radiation in the part of the electromagnetic spectrum where there is insufficient energy to cause ionization. It includes electric and magnetic fields, radio waves, microwaves, infrared, ultraviolet, and visible radiation.http://www.who.int/ionizing_radiation/about/what_is_ir/en/

author: helius
author_rank: Super Contributor
timestamp: January 12, 2016, 09:44:15 am
content: Ultraviolet A (UVA) radiation is not ionizing, but it does cause cancer by an indirect route, through formation of free radicals in the cell nucleus (a free radical is not an ion and will form at below the ionization potential). Ultraviolet B (UVB) radiation, although higher in energy than UVA, is also too weak to cause ionization, but it can damage DNA directly by forming thymine dimers. Indeed most organic chemistry happens at energy levels that are below the ionization potential.This idea that energy that is less intense than X-rays is therefore biologically harmless is very strange, and one wonders what kind of warped thought process gave rise to it.

author: Srbel
author_rank: Frequent Contributor
timestamp: January 12, 2016, 09:53:31 am
content: Quote from: Richard Crowley on January 09, 2016, 08:37:26 pmWelcome to my ignore list, Richard.

author: coppice
author_rank: Super Contributor
timestamp: January 12, 2016, 10:10:37 am
content: Quote from: helius on January 12, 2016, 09:44:15 amUltrasound can also be locally focussed by turbid biological fluids to an intensity that will break DNA chains. Modern medical ultrasound equipment appears to be entirely safe, but some of the early stuff used really high intensity levels. It used to worry some people I knew in the medical device industry at that time.

author: Brumby
author_rank: Unknown
timestamp: January 12, 2016, 11:09:25 am
content: Quote from: helius on January 12, 2016, 09:44:15 amThis is an example of one thereactions i had to the "Non-ionizing (non harmful)" heading.

author: vk6zgo
author_rank: Super Contributor
timestamp: January 13, 2016, 10:26:04 am
content: Quote from: Brumby on January 12, 2016, 11:09:25 amAs a general rule itiscorrect.Despite all the panic,you have to spend a long time in the sun or a "sunbed" to get skin cancer.Statistics of exposure to RF over many years,& many people have shown no correlation between such exposure & cancer,or any other ailment.Humans are a lot tougher than is popularly believed---they have been exposing themselves to massive amounts of electromagnetic radiation in the form of heat from open fires for millennia.

author: amyk
author_rank: Super Contributor
timestamp: January 13, 2016, 11:46:59 am
content: Quote from: MrSlack on January 11, 2016, 08:48:00 amThe real danger with microwaves is getting it in the eye, which does not sense heat and can easily get cooked. Otherwise it is entirely a thermal effect.

author: timb
author_rank: Super Contributor
timestamp: January 13, 2016, 11:59:59 am
content: Quote from: Richard Head on January 11, 2016, 09:49:41 amFun Fact: A woman puts you inside her and later is diagnosed with cervical cancer. You could actually be the cause.This message brought to you by HPV, the *new* sharing is caring disease.

author: Brumby
author_rank: Unknown
timestamp: January 13, 2016, 02:20:16 pm
content: Quote from: vk6zgo on January 13, 2016, 10:26:04 amA "general rule" that it's ok - followed by a statement that (at whatever dose) it is not? This then begs the exact question I have put -where do you draw the line?As for the 'heating effects' - areallheating effects benign? If not, then the question arises once again - where do you draw the line?

author: tggzzz
author_rank: Super Contributor
timestamp: January 13, 2016, 03:23:59 pm
content: Quote from: Brumby on January 13, 2016, 02:20:16 pmNo, heating effects are not necessarily benign. The worst case for cellphones is the cornea, since it is exposed and has a poor blood supply so heat is poorly removed an it experiences larger temperature rises. Basically the cornea is "cooked" and cataracts form.The critical factor is the temperature(s) at which the protein(s) in the cornea start to "denature" (an obsolete concept meaning "change shape") as they do when cooked. The rate of deterioriation is typically an exponential factor based on that temperature. The only remaining factor is the relationship between incident power/frequency, and temperature rise.Both the temperature and rate are easily measured in the lab and are well understood. Similarly the relationship between power, frequency and temperature rise is easily determined by experiment. In short, all those factors are well understood.Are there other factors? Despite looking for many decades, none have been found. If someone makes the extraordinary claim there are other factors, it is up to them to provide extraordinary proof. It isnotup to others to refute any such claims.

author: helius
author_rank: Super Contributor
timestamp: January 13, 2016, 03:32:17 pm
content: I am not aware of any results that show a specific sensitivity to RF. However, scalar electric or magnetic fields have been studied in relation to biological effects for many decades: from changing plant growth patterns to altering consciousness, their effects are many.

author: VK5RC
author_rank: Unknown
timestamp: January 14, 2016, 09:51:28 am
content: Remember that frequency of the EMR is a critical factor, EMR does not start to ionise molecular bonds till the soft X-Ray portion of the spectrum, as Radiant heat is a lot closer to that potion of the spectrum than radio, the EMR worried guys should be MUCH more worried about the radiative heater (hundreds of watts and you sit next to it for hours) or wood fire than mobile phones or WiFi.

author: Zero999
author_rank: Super Contributor
timestamp: January 14, 2016, 04:29:23 pm
content: Quote from: VK5RC on January 14, 2016, 09:51:28 amIR and the high microwave end of the spectrum is absorbed at the surface. The danger with RF is lower frequencies penetrate the human body more deeply and can harm internal organs such as the brain.

author: Tinkerer
author_rank: Frequent Contributor
timestamp: January 15, 2016, 11:35:28 pm
content: I took a class on bioelectrics once and looked at the data. The effects from all this EM stuff is either nonexistant or on the order of .01% increase in cancer rates.In other words, its not really worth worrying about if any effects even do exist.

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 16, 2016, 12:02:57 am
content: Quote from: Tinkerer on January 15, 2016, 11:35:28 pmBe careful what you say. Srbel may put you on his ignore list!

author: Dongulus
author_rank: Regular Contributor
timestamp: January 16, 2016, 01:23:24 am
content: Quote from: NANDBlog on January 11, 2016, 10:22:14 am

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 16, 2016, 01:37:23 am
content: Quote from: NANDBlog on January 11, 2016, 10:22:14 amThey have been predicting for a long time having "smart toilets" that could do urinalysis "on the fly".We already have home medical equipment that have built-in cell phones so the docs can check up on you. Dunno whether they "push" data or are available to "polled" on demand? (Or maybe some of each kind.)The medical school at the uni where I used to work has the world's first proton accelerator outside a research lab. Its about half the size of the Australian Synchrotron. It is used exclusively for medical treatment and they have several output beams which are scheduled almost 7x24x365. I know several people who were treated for prostate cancer there. Apparently you can manipulate protons so the beam focuses at some distance from the lens, reducing heating/damage to unaffected tissue. But I'm not familiar enough with the physics and I've never studied it at depth.

author: Brumby
author_rank: Unknown
timestamp: January 16, 2016, 02:12:34 am
content: Quote from: Tinkerer on January 15, 2016, 11:35:28 pmThis might be correct for everyday situations - but there is no such qualification in statements like these.I could specify a set of conditions that anybody here with RF experience would get cold shivers, so there IS a point at which danger exists - where my question still stands: "Where do you draw the line?"Let me throw thisvery specificscenario out there for comment:Conditions:* Type of energy: Unmodulated carrier RF* Frequency: 2.4GHz* Exposure time: 1 hour* Power:1uW - - - - - - - 1mW - - - - - - - 1W - - - - - - - 1kW - - - - - - - 1MW - - - - - - - 1GWWhere do you draw the line?

author: vk6zgo
author_rank: Super Contributor
timestamp: January 16, 2016, 04:12:22 am
content: Quote from: Brumby on January 16, 2016, 02:12:34 amSorry,but that isn't specific at all.Are you talking aboutreal power( I^2R) or EIRP?If real power,what kind of antenna? (The signal strength in any direction,of an isotropic radiator fed with 1kW will look like that of a 30dB gain antenna fed with 1W in its direction of maximum directivity .)How far away?

author: Red Squirrel
author_rank: Super Contributor
timestamp: January 16, 2016, 04:29:37 am
content: Personally I prefer to go wired for anything stationary, not because of it being "harmful" but just because you need to run power to it anyway, or mess with batteries. If you have 50 different gadgets around the house that are running on batteries even though it can last years you will find yourself at some point having to change all these batteries. If you have something that's wired and self contained it's always powered, and it's also safe from any potential hackers that may be able to heck said devices... a lot of these "smart home" things arn't made with security in mind at all. I rather have everything wired to a central server, then make that server available on the wireless network if I want to control it from a phone. At least it's a single point of security to worry about. It also means less RF in the air and less potential for interference.Now start modifying these things to transmit in the kw range, and yeah, you might get cancer.Most wireless devices tend to transmit in the mw range I believe. (mili, not mega).

author: tggzzz
author_rank: Super Contributor
timestamp: January 16, 2016, 08:27:18 am
content: Quote from: Brumby on January 16, 2016, 02:12:34 amYou asked that question before and I provided you with the answer, and the answer has not changed. I suggest you read it.Note that at 2.4GHz the answernhas been very well studied, and that domestic microwave ovens leak up to 1W and that people stand very close to those. I would not put my eyeballs anywhere near a domestic microwave oven with unknown provenance.

author: miguelvp
author_rank: Super Contributor
timestamp: January 16, 2016, 08:32:58 am
content: Who has the signature: don't become the antenna? I think it's Sue but not sure (no pun intended)

author: Brumby
author_rank: Unknown
timestamp: January 16, 2016, 11:24:03 am
content: Quote from: vk6zgo on January 16, 2016, 04:12:22 amOK - let's go for EIRPQuoteN/AQuoteFor a number, how about 1m.Anything else needed?Quote from: tggzzz on January 16, 2016, 08:27:18 amA response was posted, but the question was not answered.Quote... yet here you acknowledge the very issue I have been trying to address. On these, your very own words: "anywhere near" I ask - just how close do you mean?My point in all of this is rather simple - and I have tried to make it clear. At some point much, if not all, radiation - both ionising and non-ionising - becomes harmful. I simply want to know when that transition occurs - and if it's a fuzzy line, just how fuzzy it is.Yes, I know there will be a number of parameters - frequency, power, duration, distance, etc., etc., etc. and certainly the conditions are not likely to be commonly occurring (we would hope) - but nobody here seems to want to look past the simplistic answers.

author: tggzzz
author_rank: Super Contributor
timestamp: January 16, 2016, 03:37:49 pm
content: People have spent a lot of time and money looking "beyond the simplistic answers". The non-simple answers are, unsurprisingly, complex.What research have you done to try and find the answers?Expecting people here to provide very long answers to a casual question is, um, optimistic. You will have to do the research necessary for you to be able to know all the parameters that affect the answer. And then you will have an appreciation of why answers cannot be exact.

author: Brumby
author_rank: Unknown
timestamp: January 16, 2016, 04:18:47 pm
content: Quote from: tggzzz on January 16, 2016, 03:37:49 pmI am fully aware that the non-simple answers are complex.QuoteThe point of my question was not to have numerical answers dished up to me, but to see if there was anyone who was willing to concede my question had any validity and try to address it. Most of the responses were dismissive - and your latest one was the only one that stood out as at least declaring the issue as being a complex one to answer. It would seem I should now take the horse as dead and completely flogged.I do not doubt that I have annoyed some of the members here and for that I do apologise - but not for asking the question.Nevertheless, at this point I will step down from the soapbox.

author: Zero999
author_rank: Super Contributor
timestamp: January 16, 2016, 06:52:10 pm
content: Quote from: Brumby on January 16, 2016, 11:24:03 amThat's still not enough information.Does the beam spread or is it concentrated energy?For example, a couple of minutes of exposure to near IR, UV and visible light from the sun will not cause any damage, even on clear day, at the top of a mountain, at midday on the equator, but concentrate the energy using a magnifying glass or parabolic mirror and it can cause severe burns.

author: Brumby
author_rank: Unknown
timestamp: January 17, 2016, 01:57:20 am
content: Quote from: Hero999 on January 16, 2016, 06:52:10 pmIf I have it right, the parameter you're homing in on here is W/m2- and it is certainly key to answering the question quantitatively, but for the sake of argument, let's just pick an average microwave antenna that you might find in a place like this:But before this continues into farce (and I'm sure some will say 'too late'), I would like to cut to the chase...Even if all the parameters you wish to throw down as a challenge are defined - would youthenattempt to answer the question?I somewhat suspect the answer is 'not really'. If so, this highlights the point that I have been trying to show - that we can are fairly clear about very low levels being safe and very high levels being unsafe, but we don't have much confidence in defining the risks over the transition zone or even where the transition zone starts and ends.

author: Bob F.
author_rank: Regular Contributor
timestamp: January 17, 2016, 02:13:03 am
content: Quote from: Richard Crowley on January 16, 2016, 12:02:57 amAnd not even with any warning whatsoever! Now that can't be fair surely? I think you should apply for compensation - clearly your Human Rights have been violated... Oh, the inhumanity!

author: vk6zgo
author_rank: Super Contributor
timestamp: January 19, 2016, 07:08:16 am
content: Quote from: Brumby on January 17, 2016, 01:57:20 amParabolic dish antennas are designed to convert diverging rays into parallel rays( OK ,wavefronts are not really rays,but it is how such reflectors are explained,both in optics & antenna descriptions)Imagine ,a Parabolic dish used as a receiving antenna:-Parallel rays from the remote station strike the dish,are reflected at an angle depending upon its curvature at that point,& all converge at the focal point of the Parabola,where the feed device,(let us assume,a dipole)is situated.The transmit case is the converse of the above.The RF signal is radiated from the dipole into the dish,& is reflected as parallel rays which then proceed to the remote receive antenna.There is only one “focal point” with such an antenna,& that is where the feed device is situated.Even if it were possible to "focus RF signals to a point"somewhere in mid-air using such antennas,there is nowhere in Communications where such a thing would be useful.Note on EIRP:-Say the dish has a specified gain of 28dB &,the dipole has a gain of around 2dB,both w.r.t Isoptropic,for a total gain of 30dB.If the dipole is driven with 1 Watt of RF,to the remote receiverthe signal strength received is the same as that which would be supplied by an Isotropic antenna driven with 1kW.Remember,however,the original 1W is all you have to work with,distributed across the whole area of the Dish.If you suspend yourself 1m in front of the dish your body will only intercept some of that 1 Watt.To the signal,you are two dimensional---parts of your surface area which don’t face the antenna don’t count.I don't think your question is something that can be easily resolved.The RF Exposure Rules are extremely conservative,for that very reason.Frequency is important-----I have spent longer than 1 Hour within a few metres of the base of an MF Radiator fed with 60+kW.& longer than that on another occasion working in close proximity to a HF curtain Array fed with 50kW.I have also spent the best part of an hour behind VHF antennas fed with 10kW (EIRP 100kW).I would be very wary of Microwave signals at such levels.Quite apart from the fact that high gain antennas usually make it unnecessary to produce extreme levels ofrealpower at Microwave frequencies,most people do not spend a lot of time in front of such antennas because by their very nature they are "up in the air".Maritime & Military people are more likely to be exposed to high levels of Microwave RF power,due to the fact that RADAR does producerealpower levels in the kW region,as witness folks getting eye damage by looking down waveguides.

author: Brumby
author_rank: Unknown
timestamp: January 19, 2016, 08:22:58 am
content: I appreciate your effort in examining the scenario in detail, but you could have stopped with this:Quote from: vk6zgo on January 19, 2016, 07:08:16 amI most certainly agree - but however easy or difficult it may be, the implications of getting it wrong are somewhat of a concern.Quote from: vk6zgo on January 19, 2016, 07:08:16 amThat is reassuring - but my interest has been justhowconservative they are, which is only really going to be apparent when the range of transition from safe to unsafe has been defined.We certainly seem to know enough to keep safe enough - but I don't think it can be said we know everything.

author: Zero999
author_rank: Super Contributor
timestamp: January 19, 2016, 12:14:27 pm
content: At low frequencies, it just not possible to focus the radiation into an intense beam because the wavelength is so large. I'd also suspect the wavelengths much larger than the human body are low risk because they won't be absorbed, unless you're in the near field or near something which could act as an antenna.

author: vk6zgo
author_rank: Super Contributor
timestamp: January 19, 2016, 03:24:55 pm
content: Quote from: Hero999 on January 19, 2016, 12:14:27 pmNormal antennas do not "focus" the radiation "into an intense beam",as there is no practical purpose in so doing.Maybe an "Evil Genius" might do that,but we are dealing with normal Communications & Broadcast Antennas.

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 19, 2016, 06:23:36 pm
content: Quote from: vk6zgo on January 19, 2016, 03:24:55 pmA great many antennas focus RF beams. Every parabolic dish and directional antennas of several varieties "focus" radiation.There are excellent reasons for focusing RF both at the transmitting end and at the receiving end.Everyone who watches satellite TV understands that. Anybody who has seen microwave dishes has seen it at work.The definition of "intense" is ambiguous and undefined.

author: Zero999
author_rank: Super Contributor
timestamp: January 19, 2016, 08:05:40 pm
content: Quote from: vk6zgo on January 19, 2016, 03:24:55 pmBut an antenna can convert the radio waves into electricity which can cause nasty burns.Take a person who's 1.75m standing near a huge 1MW 1MHz transmitter. All will be fine because the wavelength is 300m and they're a tiny fraction of that. Now put the person between two 150m long metal poles, forming a1/2wave dipole and they'll get zapped.

author: vk6zgo
author_rank: Super Contributor
timestamp: January 20, 2016, 12:20:37 am
content: Quote from: Richard Crowley on January 19, 2016, 06:23:36 pmThe "focussing" is between the feed point and the dish itself---the signal leaves the transmitting dish as parallel rays,which do not converge again (in fact,they diverge) until they reach the receiving antenna.The region of the most intense RF energy is directly at the feedpoint.Many people believe that 'gain antennas" have real power gain,& that 1kW EIRP can perform the same amount of work as 1kW ofrealpower (including cooking unwary passers-by).This is,of course,nonsense,as it implies "over-unity".Our hypothetical "Evil Genius" would have to approach the problem from another direction.Perhaps an array of collinear elements (covering an area equal to that of a dish),fed with high power & mounted directly in front of that dish.At the "focal point"would be another small dish,firing through a hole in the middle of the main dish,then some other hardware producing an adjustable focal point he could use on "Mr Bond".

author: Brumby
author_rank: Unknown
timestamp: January 20, 2016, 01:29:51 am
content: Quote from: vk6zgo on January 19, 2016, 07:08:16 amHere's a question:If it is so darned difficult to define a scenario, then how is it possible for the "RF Exposure Rules" to have any practical meaning?

author: helius
author_rank: Super Contributor
timestamp: January 20, 2016, 01:56:35 am
content: There's a well-known logical fallacy called the Argument Of The Beard. It goes something like: We would like to prove that there is a real difference between being clean-shaven and being bearded. But no one can agree just how many face hairs must one have, or how long they must be, to be a beard. Any precise definition would be arbitrary, for we could ask, What is the reason you do not draw the line a little lower, or a little higher? and you would have no good answer. So, we cannot show any difference between clean-shaven and bearded. Thus the fallacy.It's commonly accepted that there are safe levels of RF, and there are dangerous levels of RF. They are sufficiently different in terms of their effects that it is easy to tell between them (just like beards). The fact that there are intermediate levels which are not obviously safe or obviously dangerous can't affect that.

author: Brumby
author_rank: Unknown
timestamp: January 20, 2016, 02:21:43 am
content: From what you have said, the "Argument Of The Beard" is based on an opinion. Defining safe levels of RF exposure is, to my mind, directly associated with measurable impacts on human health.Quote from: helius on January 20, 2016, 01:56:35 amMy prime interest isinthose intermediate levels.

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: January 20, 2016, 07:07:51 am
content: Quote from: helius on January 20, 2016, 01:56:35 amSolution is simple.In Hegelianism that later was developed into Dialectical Materialism this is described as transformation of quantity into quality.https://www.marxist.com/science-old/dialecticalmaterialism.html#Quantity and Quality.For this case of harmful radio waves we should use analogy of nuclear reaction - if we have few atom of Plutonium they will emit some electrons that will set other atoms in chain reaction but if we don't have many atoms of Plutonium reaction will die out. If we have enough - we have an explosion. So in case of RF radiation if organism is exposed to amount of power that is small enough that it can heal itself faster than it receives damage then we definitely say it is NOT harmful and otherwise it is harmful. Now that amount of RF radiation became very clear definitive quantity. Following this idea we can calculate which hair will make beard, which atom of plutonium will make it go bOOOOm and we know what amount of RF power will cause harm.

author: VK5RC
author_rank: Unknown
timestamp: January 20, 2016, 08:28:46 am
content: For measurable effects the "beard" issue is not a problem, the standard measure is the LD50. The lethal dose that kills 50% of an aged standardised population. For ionising radiation these levels to approximate values (order of magnitude) are known. RF radiation can heat and can therefore kill/main but those levels are exceptional but again reasonably known. The idea that at levels of uncertainty, i.e. whether you get burns or not, does not mean that there is uncertainty of effect e.g. it gives you cancer. (or NOT)The other good place to look for RF safety is in the epidemiological data, in the last 15-20 yrs the number of people sticking a small and modestly powerful RF transmitter right next to their head for hours a day has skyrocketed. perhaps 100,000x compared to 1960s levels, yet the number/distribution of illnesses has NOT followed such a trend.In my mind the most dangerous aspect is the bus I have seen people nearly walk into while talking on the phone.