Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: Prev 1 [2] 3 Next   Go Down
  Print  
Author Topic: Dangers of an indoor antenna.  (Read 11244 times)
KC8VWM
Member

Posts: 3119




Ignore
« Reply #15 on: March 02, 2012, 10:11:18 PM »

Please provide any single incident or existing example where it was documented where any antenna installation caused some sort of disease to occur. Let me save you some time.. There are none.

The percieved "danger" you speak of is sheer nonsense, because it's merely a large scale public perception that exists without any scientific documented facts.

It's kinda like saying ghosts are dangerous...
« Last Edit: March 02, 2012, 10:21:39 PM by KC8VWM » Logged
W0BTU
Member

Posts: 1672


WWW

Ignore
« Reply #16 on: March 02, 2012, 10:20:23 PM »

Please provide any single incident or existing example where it was documented where any antenna installation caused some sort of disease to occur.

The percieved "danger" you speak of is sheer nonsense, because it's merely a large scale perception yet it exists without any documented facts.

Bingo! I asked that same question several days ago in this thread, and so far, it has been met with complete silence. But we're waiting. :-)

The idea that RF at HF has ever hurt anyone in the slightest degree is utter nonsense. Period.

People have been exposed to RF at FAR higher levels than any ham has, with ZERO ill effects.

Can you say "paranoia"?  Wink



There are people who are exposed to a LOT more HF RF than amateurs are. When we visited the old Voice Of America radio station in Bethany, Ohio years ago, they had a huge 20 dB gain Sterba curtain antenna fed with a 250 kW transmitter. That's 2.5 million watts of ERP, my friend. There was so much RF in front of that antenna that you could sometimes hear the program audio emanate from tiny arcs in a low, rusty barbed wire fence along the road in front of that huge Sterba.

You know what was right across the road from that enormous Sterba and the talking fence? Houses with families living in them.

I'm not saying I would have wanted to live in one of those houses, but I think it's a safe bet to say that no one there looked like they had been at Hiroshima, Nagasaki, or Chernobyl.

This thread reminds me of something I did over 30 years ago. I had a 3' dia. receiving loop made from 1/2" hardline, not more than 3 feet from my operating position. One day I decided to feed it with as much power as an SB-220 would put out with 140 watts drive. Other than the extra eyeball growing on my face, I don't think it affected me. :rolleyes:
« Last Edit: March 02, 2012, 10:46:52 PM by W0BTU » Logged

KC8VWM
Member

Posts: 3119




Ignore
« Reply #17 on: March 02, 2012, 10:33:15 PM »



People have been exposed to RF at FAR higher levels than any ham has, with ZERO ill effects.



You mean like the people who work at the 1000's of radio stations across the country every single day who are exposed to 50,000 watts or more RF power for 5 days a week for 30 years of thier lives?

Funny how we have never heard of any TV weatherman dropping dead because of all the RF they were exposed to from the station they worked at over the years.



Logged
W0BTU
Member

Posts: 1672


WWW

Ignore
« Reply #18 on: March 02, 2012, 10:40:29 PM »

... You mean like the people who work at the 1000's of radio stations across the country every single day who are exposed to 50,000 watts or more RF power for 5 days a week for 30 years of their lives?

Funny how we have never heard of any TV weatherman dropping dead because of all the RF they were exposed to from the station they worked at over the years.

And we never will. See http://forums.qrz.com/showthread.php?278460-RF-exposure-question

So when is all this false information about how RF can hurt a single flea going to end?

And exactly WHERE did this nonsense get its start?

Whoever started this rumor ought to go to jail.  Grin
« Last Edit: March 02, 2012, 10:49:32 PM by W0BTU » Logged

W6RMK
Member

Posts: 651




Ignore
« Reply #19 on: March 03, 2012, 05:46:20 AM »


The idea that RF at HF has ever hurt anyone in the slightest degree is utter nonsense. Period.

People have been exposed to RF at FAR higher levels than any ham has, with ZERO ill effects.

I guess you haven't read IEEE/ANSI C95.1-2005, which is the RF exposure standard.  It's got about 100 pages of analysis in there, and yes indeed, there are plenty of cases where people have suffered ill effects from exposure to RF. Notable cases are crewmen on an aircraft carrier where significant VHF power was coupled through them between an aircraft on the deck and the deck, leading to ankle and wrist pain.  There are also numerous documented cases of people exposed to high RF power in transmitter and radar situations with burns and injuries, not to mention thyroid damage and cataracts.  There's a reason for the "don't look into the open waveguide with your remaining good eye" signs are around.

There's a ironically humorous FCC enforcement action from about 10 years ago where a worker was up a tower with a FM transmit antenna running at reduced power. Station manager was getting calls during drive time about the signal being weak, so he jacked the power back up.  The tower jockey's protective clothing caught fire.

In general, the limits are set based on documented thermal effects.  The cancer/RF connection is more tenuous. There's been some studies in vitro, and some more recent studies with cellphone exposure, but it's not conclusive.

The maximum permissible exposure for "controlled exposure" (i.e. you're working with it) is typically set at 1/10th of the level where effects have been seen. The MPE for "uncontrolled" (i.e. general public) is typically 1/10th of that.

Quote

There are people who are exposed to a LOT more HF RF than amateurs are. When we visited the old Voice Of America radio station in Bethany, Ohio years ago, they had a huge 20 dB gain Sterba curtain antenna fed with a 250 kW transmitter. That's 2.5 million watts of ERP, my friend. There was so much RF in front of that antenna that you could sometimes hear the program audio emanate from tiny arcs in a low, rusty barbed wire fence along the road in front of that huge Sterba.
And because that antenna is huge, the power density is fairly low.  If it's 20 dB and 250kW, that's 25 MW E*I*RP, but it's still just 250 kW being radiated, just over a smaller angle than the whole sphere.   The Delano VOA station radiated 500kW in a 12/6/0.5 array.. that's 12 dipoles wide and stacked 6 high, so it covers a huge area. Say they were radiating on 40m.. those 12 dipoles mean the antenna was 240 meters wide and probably half that high.   Spread 500kW across 20,000 square meters and the power density gets pretty low (25W/m2 or 2.5mW/cm2)  which is way below the MPE..
(MPEs are frequency dependent, but 10mW/cm2 for controlled exposure is about as low as they get)

As a practical matter, the EPA measured the field at the fence by the Delano VOA station (because of a suspected cancer cluster in McFarland) and I think the peak was <10V/m E field, which is about 0.025 mW/cm2.     

Quote
You know what was right across the road from that enormous Sterba and the talking fence? Houses with families living in them.

I'm not saying I would have wanted to live in one of those houses, but I think it's a safe bet to say that no one there looked like they had been at Hiroshima, Nagasaki, or Chernobyl.
because the field isn't all that high.  Stand in front of a 10kW average power magnetron fed into a horn, and you've got problems.
Quote
This thread reminds me of something I did over 30 years ago. I had a 3' dia. receiving loop made from 1/2" hardline, not more than 3 feet from my operating position. One day I decided to feed it with as much power as an SB-220 would put out with 140 watts drive. Other than the extra eyeball growing on my face, I don't think it affected me. :rolleyes:

That's hardly a valid test, and you know it.
Logged
W6RMK
Member

Posts: 651




Ignore
« Reply #20 on: March 03, 2012, 05:47:53 AM »

Quote from: W6RMK

146 MHz = a bit more than 2 meter wavelength.  6 feet away is only two wavelengths..



Just under 1 wavelength, actually.
doh..

ok, so you're definitely in the near field...
Logged
G3RZP
Member

Posts: 4591




Ignore
« Reply #21 on: March 03, 2012, 06:40:35 AM »

I know a guy in his 80s who worked for many years at HF and lower VHF stations with BIG tx's - like 6 off 100kW HF plus smaller stuff. The effect on him is that he lets his wife wash the dishes, cook and clean - he never does - and whenever possible, have other people pay for his beer - or wine - or whisky.

Must be the long term effects of RF exposure!
Logged
AC5UP
Member

Posts: 3872




Ignore
« Reply #22 on: March 03, 2012, 07:04:18 AM »

Stand in front of a 10kW average power magnetron fed into a horn, and you've got problems.

Back in the early 70's I was told that anything beyond a brief exposure to the business end of a five watt microwave link might try to cook your bone marrow and this was well before most of us had heard the words "microwave oven" used together. Damaged bone marrow won't drop you off the tower like a bad habit, but it does improve your odds of developing blood related disease(s) down the road. Which in turn paves your path to a premature demise...

And that's why it needs to be repeated that any time you're dealing with any chronic disease, or cancer in particular, there can be years if not tens of years between the cause and onset of symptoms... More than enough time to make the relationship difficult to find.

If any of you have an interest, take a look at this: http://www.alz.org/downloads/Facts_Figures_2011.pdf

We are on the verge of a modest epidemic in Alzheimer's. Partially due to the aging of baby boomers, partially due to genetic traits and also by geographic distribution. And that's what makes it an intriguing puzzle. Hispanics have the highest rates of occurrence compared to Caucasians and Negroes, yet the northwest states show the highest rates per capita in the country despite modest representation by the riskier populations. Researchers can't tell you what causes Alzheimer's.

Which....... To paraphrase WØBTU...... Can inspire comments like: " No one can give you one, not one, case of anything causing Alzheimer's. Therefore it's a phony disease. If it has no cause it's just a scam and the people who invented the rumor ought to go to jail... "
Logged

Never change a password on a Friday                
K4SAV
Member

Posts: 1840




Ignore
« Reply #23 on: March 03, 2012, 08:54:13 AM »

Whether RF radiation can cause cancer is certainly debatable, but fortunately we don't have to do that.  Besides, I seriously doubt there is anyone on this forum qualified to determine if RF exposure is harmful.  Of course that doesn't mean you can't express your opinion.  As radio amateurs, we have a rule that requires us to do an RF assessment and to abide by the rules in that document.  Those limits were based on a best guess (lacking conclusive data) and are likely to be very conservative.  So you see, whether it is harmful, or not, doesn't matter, we still have to abide by the rules. 

The RF safety rules which we have to follow are contained in this document:
http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/oet65b.pdf

RF safety calculators, as W6RMK pointed out, have some limitations especially in the near field.  The best way to evaluate an antenna is to model it in EZNEC (or 4NEC2).  You can plot the E fields and H fields at any location and compare the results to the limits in the document listed above.

From the Appendix of that document, for the general population, the E field limit on 2 meters is 27.5 V/m, and the H field limit is 0.073 A/m.  You get to derate that number based on the duty cycle that you actually transmit, and that also varies by mode of operation.  You can get that data from the document and do the derating.  I don't know you use the radio, but I can give you the 100% duty cycle number.

I quickly plotted the E and H fields from a 2 meter Slim Jim made with ladderline and with 45 watts applied.  I ignored the feedline common mode currents, which are always significant with these antennas (and likely to cause higher fields at the operating position).  I put the antenna at 10 ft height.  The E field limit was exceeded at about 5.4 ft from the antenna. The H field was exceeded at about 5.6 ft from the antenna.   Remember those are for a 100% duty cycle and a low duty cycle will allow less distance. 

If you use EZNEC, notice the disclaimer on the EZNEC output.  W7EL doesn't claim to know anything about RF safety of antennas either, although this software is capable of calculating the RF field strength.  That's all you need to know too.

Jerry, K4SAV
Logged
W6RMK
Member

Posts: 651




Ignore
« Reply #24 on: March 03, 2012, 09:35:58 AM »

Whether RF radiation can cause cancer is certainly debatable, but fortunately we don't have to do that.  Besides, I seriously doubt there is anyone on this forum qualified to determine if RF exposure is harmful.  Of course that doesn't mean you can't express your opinion.  As radio amateurs, we have a rule that requires us to do an RF assessment and to abide by the rules in that document.  Those limits were based on a best guess (lacking conclusive data) and are likely to be very conservative.  So you see, whether it is harmful, or not, doesn't matter, we still have to abide by the rules. 

The IEEE/ANSI standard (from which OET Bulletin 65 limits are derived) has the research that establishes the safety limits. It's not opinion.  Let's be clear here, while cancer connection is sketchy, damage from thermal effects is fully substantiated and backed up by data.  There is *tons* of data on what power dissipation causes a burn, *tons* of data on absorption (particularly at non-microwave frequencies), so there's no doubt about the harm resulting from excessive RF exposure, any more than doubt about harm resulting from grabbing onto a 440VAC power line.  I'll bet there's more than one person reading this who has actually gotten an RF burn.

The safety limits are NOT talking about instant death.  They are talking about injury or measurable adverse effects.  You might consider accidentally smashing your finger with a hammer benign, but it's an injury none-the-less.

The limits are also set lower for the casual public, because they, presumably, are not deriving any benefit from the exposure, so their presumed risk tolerance is less.  This is true for virtually all "exposure to hazard" kinds of safety rules and is no different for EM fields.

Quote
The RF safety rules which we have to follow are contained in this document:
http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/oet65b.pdf

One thing to keep in mind, when considering chronic vs one-time exposures, is the cumulative effect over time.  So far, there appears to be no such cumulative effect for EM fields (a few studies showing correlation with some cancer, but nothing conclusive, yet) as there is for ionizing radiation or things like smoking.  (that is, one cigarette won't cause any appreciable damage, smoking them for years definitely will)

Limits are all the more important when it comes to your neighbors and the general public. I don't much care if you want to go out and juggle running chainsaws in your backyard, but I certainly don't want you doing it with me standing next you, exposing me to the hazard.

Do the analysis, keep the records.  It's not that hard. 
Logged
W0BTU
Member

Posts: 1672


WWW

Ignore
« Reply #25 on: March 03, 2012, 10:50:00 AM »


The idea that RF at HF has ever hurt anyone in the slightest degree is utter nonsense. Period.

People have been exposed to RF at FAR higher levels than any ham has, with ZERO ill effects.

 Notable cases are crewmen on an aircraft carrier where significant VHF power was coupled through them between an aircraft on the deck and the deck, leading to ankle and wrist pain.  There are also numerous documented cases of people exposed to high RF power in transmitter and radar situations with burns and injuries, not to mention thyroid damage and cataracts.  There's a reason for the "don't look into the open waveguide with your remaining good eye" signs are around.

I don't dispute the dangers of RF at those frequencies at all. Please note that I specified "HF", and not VHF, UHF, or microwaves.

HF means below the six meter band, and that's where the lack of evidence I spoke of is. It seems to me that 10 meters and lower has been incorrectly included in what can harm us. When I see reliable proof of harm at HF, and especially at amateur power levels, I'll reconsider.
Logged

W6RMK
Member

Posts: 651




Ignore
« Reply #26 on: March 03, 2012, 11:29:23 AM »

This applies at HF too, not just microwaves and UHF. 
It's all about heat absorption and getting cooked, literally.
(there's also a "shock" issue, but that comes up a lot less frequently with RF)

Here's some basic numbers:  Sunlight is about 800 Watts/square meter, or 80 mW/square centimeter.   If I took you out, dressed you all in a black ninja suit and staked you down in the noon sun, you'd be in a world of hurt after an hour or two.  Maybe you'd have heat stroke, maybe not, but nobody would argue that this is totally benign.
Likewise, if you hold a 25 watt lightbulb in your hand (about 250 square centimeters), you're getting exposed to about 100 mW/cm2, and that's going to be pretty uncomfortable if you keep it up for long, and it might result in damage.

So the problem with RF, particularly at MF,HF and VHF is this.. it gets absorbed throughout your body (RF skin depth is meters at those frequencies in a conductor like you).  And it gets preferentially absorbed in some tissues, so while your body as a whole may not get too hot, some pieces might, and you won't feel it.  You don't have temperature sensing nerves *inside* your body, just on the skin surface.  There's also an issue of "how much RF does a person absorb in a given field".. VHF is worst, because the body is comparable to a wavelength, so you make a real good absorber.  At lower frequencies, you absorb less.  That's why the exposure limits are higher at lower frequencies.  At higher (microwave) frequencies, the limits are higher because all the power is absorbed in the skin, and getting a "sunburn" is considered less bad than "cooking your internal organs". You're also more reflective at microwave frequencies (which is how motion detectors work, after all).

They've done a LOT of studies on what happens when you heat up various parts of your body (some on laboratory animals, some done on willing subjects, some on not so willing subjects), so there's a very well established science of "how much energy can we put into component X" of the body without causing adverse effects.  (Called Specific Absorption Rate in the literature).  They turn that into a EM field strength that will cause that energy density (using some carefully derived models of the body's RF properties, also based on measurements, some of which I've done myself).

They take those numbers, pick a nice safety margin (like a factor of 10) and draw some straight lines on the graph to make it easy to figure out, and that becomes the limit.   The reason for the safety margin is several fold:
1) you don't know if the person being exposed happens to be especially sensitive
2) you don't know if the environment the person is in happens to be bad. Full Sun falling on you if you were naked in below freezing might be wonderful, not so wonderful in 120F heat.
3) it's hard to accurately measure the field.

Don't forget that the limits are not "instantaneous" power.. they're averaged over a time period (e.g. 30 minutes).  5 minutes in the sun in that ninja suit followed by 25 minutes in the cool shade is probably not going to have the adverse affect that sitting continuously is.  Most hams are not running 100% duty cycle. Most people working near broadcast transmitters are not exposed to full field 100% of the time. (A friend tells me that on Navy ships with lots of externally mounted antennas radiating high power, they have signs in high field areas that say "Sailor, keep moving")


So when you say there are no cases of RF injury at HF, you are just wrong.  There are plenty of them, and the references are all in the back of the C95.1 spec, pages and pages of them.  Industrial accidents, diathermy treatments, etc. All at HF kinds of frequencies. This isn't some sort of speculative, oh, maybe the exposure shows up 20 years later thing.  We're talking about easily discernable acute injuries and their subsequent effects: burns, reddened skin, tissue necrosis, gangrene, the whole shooting match.

If you've ever felt that "RF tingle" on some band when you touched the mic or chassis: you've just exceeded the MPE for RF.  Odds are, you don't sit there hanging on for half an hour, though, any more than when you get zapped by touching the 110V line, you just hang on for the thrill of it: like those crazy people taking an "electric cure" at the turn of the last century.

RF burns are nasty. It turns out that unlike a DC or line frequency shock/spark, RF is high enough in frequency to not trigger the pain nerves in your skin.  The current tries to flow in the low resistance tissue (i.e. inside your skin) so they tend to be deep burns with small entrance wounds, and remarkably painless when they happen (because although the current density is high, burning the tissue, the total energy deposited is small, so it doesn't get noticeably warm). It's like having a very sharp hypodermic needle poked into you when getting a tetanus injection: you don't feel it going in, but the tissue damage or inflammation sure hurts later.
Logged
W0BTU
Member

Posts: 1672


WWW

Ignore
« Reply #27 on: March 03, 2012, 02:28:30 PM »

Yes, I know about diathermy, and I have gotten my share of RF burns. :-)

I see that I should have worded things a little differently. I meant specifically injuries from either short- or long-term, non-contact RF exposure to an antenna, and particularly amateur radio antennas below 30 MHz.

High-power radio at HF and below has certainly been around for more than a lifetime, and countless people have had a lifetime's worth of exposure to amateur, AM, and shortwave broadcast RF fields. Therefore, there certainly ought to be reliable, verified evidence of harm from that. That's what I'm saying is missing.

Do you have a link, etc. where I can go to see these many pages of injuries? I'd like to see if they include the type of exposure that I'm talking about.

I still think that Charles was right on when he posted "Please provide any single incident or existing example where it was documented where any [HF or below] antenna installation caused some sort of disease to occur. Let me save you some time.. There are none.  The percieved "danger" you speak of is sheer nonsense, because it's merely a large scale public perception that exists without any scientific documented facts."
« Last Edit: March 03, 2012, 02:33:31 PM by W0BTU » Logged

AC5UP
Member

Posts: 3872




Ignore
« Reply #28 on: March 03, 2012, 03:12:53 PM »

...if anyone reading this has been in law school, been part of a debate team, or studied logical deduction, please share a few words about how to prove something doesn't exist.  Wink
Logged

Never change a password on a Friday                
W6RMK
Member

Posts: 651




Ignore
« Reply #29 on: March 03, 2012, 08:55:28 PM »

Yes, I know about diathermy, and I have gotten my share of RF burns. :-)

I see that I should have worded things a little differently. I meant specifically injuries from either short- or long-term, non-contact RF exposure to an antenna, and particularly amateur radio antennas below 30 MHz.

High-power radio at HF and below has certainly been around for more than a lifetime, and countless people have had a lifetime's worth of exposure to amateur, AM, and shortwave broadcast RF fields. Therefore, there certainly ought to be reliable, verified evidence of harm from that. That's what I'm saying is missing.

Do you have a link, etc. where I can go to see these many pages of injuries? I'd like to see if they include the type of exposure that I'm talking about.

http://standards.ieee.org/findstds/standard/C95.1-2005.html  (and I now see you can download it for free as a pdf)

 IEEE/ANSI C95.1-2005 is where you want to look.  Plenty of references there. Probably not any citing injuries of hams that I can recall, because realistically, most hams don't have exposure issues AND if they do get hurt, they don't report it.   HF (and lower) field exposures and injuries ARE reported in a occupational context, so they do show up in the literature.  I don't have any here at home, but I can probably dig some up.

Let's bear in mind we are NOT talking about chronic exposure.  Whether you have a lifetime of exposure doesn't make a difference, other than if you are working in a dangerous place, the longer you work, the more likely you are to be injured.

The deleterious effects of RF heating are not speculative. The physiology science is there, the physics is there, there is ample evidence of tissue damage in microscopic analysis, etc.   The saving grace is that even in most cases in high fields, the exposure time is very short or low duty cycle (seconds, not even minutes), so the energy deposition is small and the corresponding heating is small, and injuries are uncommon.  That doesn't mean it's safe.

And most certainly, it doesn't mean you get to ignore the FCC rules because you don't happen to have personally witnessed an RF field injury.
Quote


I still think that Charles was right on when he posted "Please provide any single incident or existing example where it was documented where any [HF or below] antenna installation caused some sort of disease to occur. Let me save you some time.. There are none.  The percieved "danger" you speak of is sheer nonsense, because it's merely a large scale public perception that exists without any scientific documented facts."

We're not talking disease here.  We're talking acute effects: injuries and tissue damage. The same as if you held a soldering iron in your bare hand, or burned your mouth on hot pizza or coffee.  In general we are NOT talking death, dismemberment, lasting damage, crippling mayhem,  but it is damage nonetheless.  You might find it ok to get sunburned. Others may not.  As a FCC rule, you're required to make sure that nobody gets injured by your transmitters and antennas.  Pretty easy.. do the analysis, record it, and for the vast, overwhelming majority of hams, you're done. The way you get into trouble is boneheaded things like 1 meter compact loops running a hundred watts siting on the picnic table next to your rig, or poor placement of a VHF antenna with a 50W rig on a car. And even there, duty cycle is usually the saving grace.

It is quite clear that you aren't going to actually go and read the C95.1 standard, which explains all the science and WHY it is dangerous, and why it *is* a scientifically documented fact.
Logged
Pages: Prev 1 [2] 3 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!