The AM Forum

I've been involved in a QRZ thread concerning antenna resonance vs radiated field strength. This thread segued into a discussion of the effect of RF levels of intensity on the human anatomy. I'm copying my QRZ post below for consideration and comment:

"Years ago when I was more unwashed than I am today, I had a lingering pain in my right wrist. I was aware of the benefit one could obtain from diathermy treatment for such a condition.

I procured a rubber knee pad, cut it into two pieces, and slit the pieces so two 4x4-inch metal plates could be inserted. Using a 6' zip cord I connected the plates to a coil coupled to the tank of my 14 MHz final amp using two PP 304TLs.

I then positioned the two rubber-covered plates around my right wrist, turned on the amp and increased the power until I could feel the heat. I kept the heat on for ten minutes, and continued the treatment once a day for three days. The lingering wrist pain disappeared.

At that time I was unaware that I could have damaged the arm bones, but obviously I didn't. I have never performed that stunt since.

Consequently, this is my position on damage to the body from RF radiation: If the RF is in the HF range, and if you feel no heating in any part of the body, the level of RF intensity is insufficient to cause any damage to the body. I wonder where the regulators who determined the intensity level they believe causes damage to the body obtained their numbers? Did they pick them out of a hat?"

Walt

Totally non-scientific reaction...

RF heating your wrist probably won't hurt anything short term and probably long term.

Heating your head in a similar manner or getting enough heat through other RF exposure to feel, is probably bad in the short term and almost certainly bad in the long term. Your brain and some other tissues are pretty heat sensitive and may undergo cellular level changes (possible cancer).

Being a LITTLE careful seems to be common sense.

The official numbers for RF exposure from the IEEE/ANSI have been around for years, and have been selected based on being a fraction of the level that causes enough power deposition to heat tissue internally. I seem to recall 4 Watts/kg being used. After picking a number 1/10 of that level, then conversion to field units for E and H, you come up with the limits specified as xx mW/cm^2 as measured by E or H field probes and converted with free space impedance to power units. For a real good look at how it all comes about, get a copy of IEEE C95.1-1991 standard. Its big. A good book on the topic is Radio Frequency and ELF Electromagnetic Energies, by Hitchcock and Patterson (1995).

With localized medical treatments like diathermy gave, the acceptable exposure levels were exceeded locally around the pads. I have two real diathermy machines, one at 13.56 MHz Xtal controlled and one that free runs somewhere around 20-17 meters, and both do the same thing, apply concentrated electric field between pads or plates. It is important to keep the fields away from eyeballs and "other" organs (testes) that cannot dissipate the heat through blood flow rapidly enough. As for cancer, no, this hasn't been proven for HF or MF fields. UHF and VHF fields are another story since there is a problem of whole body resonances, approaching a wavelength of the applied field. The official standards do take all this into account, and reduce the acceptable levels appropriately.

Thanks for the excellent insight, John. N0WEK's comment about the brain sensitivity is also right on.

Walt

Hmmmm, this reminds me of when I used to sit on the safety committee at work. I learned quite a bit. Also one of the things I'm required to do is repair CO monitors along with different gas and LEL sensors. The one thing I found is that threshold values were generally place 100 times below the point of LDH point was. An easy example: Most CO detectors in the house trip their alarms at 35 PPM CO. The LDH threshold is 350 PPM. This keeps people from coming close to an exposure that would put them at risk. Generally speaking, our hot work permits can not exceed a LEL of 10% LEL. This runs true for most gases such as ammonia, hydrgen sulfide. I guess the point is that they intentionally place low levels as to keep people safe. The lesser, the better.

EMF's are non-ionizing radiation and have specific limits set by SAR's.

Here is an article on the latest Specific Absorption Rates (SAR)

http://www.ets-lindgren.com/pdf/sar_lo.pdf

The following is a research paper that has a lot of info.

http://www.icnirp.de/documents/emfgdl.pdf

For high power microwave studies in the lab we limited exposure to eyes because the uWave energy could heat the cornea and cause cataracts, since it does not have a cooling mechanism.

Also for FM, the length of the human body corresponds to about a half wavelength, which is why the FCC set exposure limits and minimum tower heights for FM transmission systems.

What you were doing was more like diathermy or "Deep Heat" medicine:

http://emedicine.medscape.com/article/325046-overview

Phil - AC0OB

I would venture to say that Walt is living proof that rf exposure, at least to non-critical body parts, causes minimal if any long term damage.

When I was about 19, I pulled a 1930's-40's vintage medical fluoroscope out of a dumpster, re-filled the transformer that had leaked dry, with oil from a pole pig (PCB no doubt), and fired up the X-ray machine.   I played with it several times, thinking I was being careful enough by staying clear of the window that the x-rays were supposed to come out of.  One time I turned it up full strap and I was able to light up the screen to moderate brilliance through a 1/4" thick steel rack panel.

I quit playing with it after I borrowed a Geiger counter and it observed that the counter gave off a sound like power line noise in a receiver, when placed on the work bench on the other side of the room while the x-ray machine was turned on, even though the beam was aimed in the opposite direction.  I moved the screen around in the vicinity of the the x-ray unit and found that there were visible hot spots off the sides and to the rear, well away from the window where the beam was supposed to exit.

At about age 35 I was diagnosed with cataracts, even though they didn't become a problem until about 5 years ago and I ended up having surgery in both eyes.  I have often wondered if the x-ray exposure was related to the cataracts, although both my parents developed them in their 60's so it could have simply been hereditary.

One thing I regret about that fluoroscope is not keeping the auto-transformer.  It had extremely good voltage regulation with output from about 60 to 120 volts in 10 steps or so, at about 25 amps.  The contacts on the switch were almost the size of a quarter.  I used it to control the plate voltage in my transmitter until I came across a 20A variac.  After I had already traded off the autoformer, I found that the regulation of the variac was very poor in comparison .

I try to not dwell on things that aren't yet a problem but it occasionally occurs to me that the whole RF exposure junk science bogey man may be the next thing antenna haters try to gin up in their agenda to have these weird looking (to me at least) zero antenna neighborhoods.  You know, the ones that have this kind of creepy look to them because they combine the look of modern homes with the 18th Century look of no antennas.

Luckily I have nothing to worry about then :D

Carl
/KPD

Unfortunately this sort of apocraphyal story provides little or no true substance. It is like saying that smoking is fine because George Burns smoked until he was 99 or 100. His long life probably was unrelated to his smoking...

What the long term effects of exposure to high level RF fields are unclear since it hasn't been studied in a large enough population afaik... sort of like the folks who live under or near those HV power lines, is there any effect long term or not??

Otoh, Rife suggested that one could target microrganisms and viruses by finding their resonant frequency - which presumably was not the same as something else in the body - and zapping them directly as a result... a neat idea, but one that has yet to prove to be practical.

Otoh, while not RF, lithotripsy (sp?) - ultrasonic sound waves - are used to blast kidney stones into little bits inside the body. So that larger concept would seem to work on some level.

               _-_-WBear2GCR

The ultrasonic work on kidney stones is purely a physical/mechanical action - completely different from any RF interaction with the human body.

I'm surprised that hasn't already happened.  Not just from antenna haters, but from the same  people who have already expressed alarm over HV power lines and other sources of 60~ electromagnetic fields.  It is easy enough to get the public into a state of panic over an unfounded fear.  Just a little misinformation carefully embedded in the stream of drivel that emanates from the boob tube. Those unsightly ham radio antennas produce dangerous radiation that may cause cancer!  Or worse still, may cause cancer in children. We hafta do it for the children.

This reminds me of a CBer we had in hour town many years ago.  He would sit at short table with a Phantom 500 Amplifier. This amp had 12 6LQ6 tubes in a string.  He took the top cover off so it would "run cooler" and had a desk fan blowing over the tubes.

This guy would sit hunched over that amp night after night and drink a 24 pack of beer. He played music, Yelled at people ect..  I was friends with his Brother. We went to his house one day and he had what looked like the worse case of sunburn in history. Major damage to his Chest, Neck and Face.  Skin falling off in patches. Just sickening.

Later, The doctor explained the "device" which was the amplifier, must be giving off Radiation.  He healed but never really looked the same. 

It was winter and the heat from the amp kept him warm so he sat there just hunched over the amp for hours a night.

A short time later,  He was on the air one night. He moved the amp away from him to his right.  He keyed down and said "oh man, One of those spring clips on the top of the tubes keeps arcing when I talk."  Then we heard.. BRRRRR and his signal went away.  He reached down to put the clip on tighter with it keyed up!.   Needless to say he suffered a major Shock. which blew out his Elbow into the metal table.  That pretty much ended his radio days.  True story...

I doubt the tubes would have caused sunburn.  That requires ultraviolet.  He may have received 1st degree burns from the infra-red, but he must have had his shirt off and been pretty numbed by the suds not to feel some discomfort.

I fell asleep in front of the heater one night, with my down jacket still on.  When I woke up, there was a big hole melted in the nylon outer layer, but I didn't feel any burns anywhere.

RF burns.. All over his Chest, neck and face.


Clark

It's appropriate.... the crowd loves it!

All of this discussion reminds me of a humorous, albeit expensive experience we had with a microwave path that we were planning to establish between two of our telephone central offices in the heart of Indiana. 

After a significant amount of study, path surveys and pre-planning, we determined that an intermediate repeater site was required to provide a reliable system.  We embarked on an effort to secure some land for a tower site and an equipment hut.  We also made the necessary contacts with local (county) government to obtain the necessary building permits and zoning clearances before proceeding.  Well, ordinarily this was just a formality, and considering the very rural nature of the area and the absence of any significant nearby residential developments, we thought that there would not be any issues.

Well……that was before a newspaper in a nearby small town got wind of our plans and started a fire-storm amongst local farmers and residents.  Their concern had nothing to do with aesthetics of towers, but rather they were concerned about exposure to radiation!  They had no significant objection to radio towers; in fact there was an existing 300’ CATV relay tower less than a mile from our proposed site.

The problem? ….In our application/notification we had called the new planned station exactly what it was:  a telecommunications microwave relay station.  Unfortunately, the locals associated the term microwave with microwave ovens.  All sorts of terrible images were racing through their minds about such an installation irradiating them and their dairy cattle with harmful radio rays.  Those people were genuinely very afraid of having such a perceived hazardous nuisance in their area.  In spite of efforts to educate them to the reality that any radiation on the ground from our proposed station would be less than that an individual would receive from the moon on a clear night, they refused to listen to any arguments and pressured the County to refuse any building permits or authorizations.  They were reminded that the CATV tower had already been constructed in the vicinity, their response was: “well that’s OK that is for TV”.  Of course, they were not realizing that it was also a microwave repeater station….actually running much more power than our proposed telephone microwave system.

Not wanting to cause significant PR damage or unnecessarily concern our neighbors and customers, we ended –up dropping our plans for the new system.  We eventually installed a fiber optic route for the needed facilities.  This was a considerably more expensive approach due to right-of way requirements and construction costs.  Of course, eventually the fiber route proved to be a good way to go and provided significantly more bandwidth capacity.

The point is, however, that the public’s perception and fear of RF radiation is probably much greater than what it needs to be regarding safety or potential for long-term harmful effects.   While standards may be needed to protect the public from unnecessary exposure to RF hazards, those standards certainly need to be realistic and not based upon unreasonable or emotional response playing upon fears and suspicion.  You thought you had problems with neighbors complaining about TVI, how about being called cow killers?

73,  Jack, W9GT

Clark,

Let's not forget our mutual friend who every time he keyed his 16 "pill" amp (or was it an 8 transistor, I forget now, I <<think>> it was 16), would go blind.  After 4 or 5 times at a CB Shootout, he said something to both of us, like "What should I do about it"...  Clark and I both replied "I think I'd stop keying the radio!".

I've been near field to a quarter megawatt before.  I was about a football field away, and it made ALL the hair stand on end.  This was from a PAIR of 120+ thousand watt (peak) transmitters, so the total could have been near a quarter megawatt, or much lower, depending on how "in phase" or out of phase they where.  Suffice to say, it didn't do any MAJOR damage.

I've worked on a mobile setup once that had 70+ kilowatts available.  At 45 thousand, the antenna blew apart, and the guy went to quarter waves, no more problems.  When that radio keyed, along with another (in the neighborhood of 100+ kilowatts total), it blew the tape out of the camcorder, fried the AC supply (which was plugged into the wall via a REALLY long antenna, err, extension cord), and the camcorder never turned on again.  Another true story.

If people really want to see what lots of RF can do, look at some of the idiots in the shootout scene.  Lots of tumors, softball sized, golfball sized, etc.  I used to attend nearly every one, but stopped after seeing some of the health effects that friends of mine where suffering.  Just isn't worth the health risks, thanks.

--Shane

Shane. I remember that..  He had an open antenna Mount less then a foot from his head with out 7000 watts.  It would get into his Optic nerve and he would lose is sight when he keyed up.. LOL

He moved the atenna to the back of the Truck and this of course stopped.

CLark

Note his head, six inches or less away from the antenna.

http://www.youtube.com/watch?v=Nxp_Nsa54_Q&feature=channel_page

Unreal...   Just unreal.

C

http://www.bigradios.com/tollfree
http://www.bigradios.com


At one time, it was the premier site.  Then I started to realize what radiation was :)

--Shane

Don, not just the antenna, but he's got the LOADING coil at his head!

What a maroon!

--Shane

Exactly, Robert.

These junk science types are relying on the public's ignorance to differentiate between IONIZING and NON-IONIZING radiation.

BTW, X-rays are considered ionizing radiation. So Don, I am glad there were no long term effects from this exposure.

 Phil - AC0OB

Jack, If folks want fear of RF, then they should go to some of the hilltop FM and TV sites on the West Coast. I forget one mentioned many times for their RF levels so dangerously high that personnel have to wear special clothing to protect themselves.

Walt, What do the "good buddies" Chicken Band, think about when they have their "keydown" and transmitting thousands of watts at 27 mhz right over their heads???

We had a similar problem to increase the height of a microwave tower to mount some bigger dishes for a 40 mi diversity link.
Fred

Not quite so different, actually similarities in the ways that I mentioned.

The ultrasonic waves are focused (somewhat) at a point in space, the object has to be able to "receive" the energy from the waves at a high enough level of absorption to cause the calcium stones to "explode". That is a resonance in effect.

The RF method I referred to presumes that some organisms are resonant at some specific frequencies, therefore will be destroyed when the energy impinges upon them at a high enough level.

The concepts are similar, the waves used different.

I said as much... I referred to "the larger concept".

             _-_-bear

Bolded emphasis mine - Al

Phil

Precisely!  I do power density calculations for a living and deal with this issue every day  HF frequencies are considered non-ionizing radiation and such considered non-carcinogenic.  Here's a link that might be helpful:

http://www.osha.gov/SLTC/radiofrequencyradiation/

A little snippet from that site:

"...Bioelectromagnetics. 2003;Suppl 6:S74-100.  Presents critiques of epidemiologic studies and experimental investigations, published mostly in peer-reviewed journals, on cancer and related effects from exposure to non-ionizing electromagnetic fields in the nominal frequency range of 3 kHz to 300 GHz of interest to Subcommittee 4 (SC4) of the International Committee on Electromagnetic Safety (ICES). The preponderance of published epidemiologic and experimental findings do not support the supposition that in vivo or in vitro exposures to such fields are carcinogenic..."

Nevertheless, There are power density limitations that are imposed on me and that's why I have to do the calculations.  Conclusion, at least for me, don't be stupid and deliberately expose oneself unnecessarily to levels higher than necessary.  See this link from ARRL:

http://www.arrl.org/news/rfsafety/exposure_regs.html

Yet another link titled "MEASUREMENTS OF ENVIRONMENTAL ELECTROMAGNETIC FIELDS AT AMATEUR RADIO STATIONS":

http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/reports/asd9601/asd9601.pdf

73 and yes,  "Switch to safety!",  Al

 

Bear said:
Not to hijack the thread but being a former service guy with the company that invented Extracorporeal Shock Wave Lithotripsy, (Dornier Medzine Technik), The shock wave is created buy using a HV power supply (shock wave generator) into a 'spark plug' which is submerged in Deionized and degassed water. The swg produces a voltage between 18K~25K VDC. which creates a shockwave at what is called F1. The spark plug is in a brass parabola of about 65%. At F1 the shockwave is 'bounced' in the parabola and reflected at a point which is called F2. This is the place where all the waves that were initially radiated come together with a combined mechanical force of about 35000psi, (its quite a bit, but a millimeter off of F2 and you feel just a discomforting pain). By using a 3 axis table/gantry, the patient is positioned by using a dual lo-flouroscopy X-ray so that the offending kidneystone is in F2. This is what pulverizes the kidney stone, (usually made of calcium oxelate) to nothing more than grains of sand. Incidentallly the machine was originally created by the Luftwaffe in the '60's to help prevent jet aircraft from being pitted by water vapor droplets when transiting from sub-sonic to sonic speeds.

Back in 1989, I was passing through Lahti, Finland, where YLE's (now dark) longwave broadcast station was located. I was fortunate enough to be walking distance from the very cool-looking T-top Marconi, strung between two self-supporting towers, about 450 feet tall. It was possible to walk right up to the chain-link fence that surrounded the transmitter building, allowing one to get to within about 40 feet of the vertical wires, connected to a feed coming through a very large glass insulator in the building. They ran (if I remember correctly) 250 kw on 254 kc, later moving to 252. The only ill effect was a memorable r.f. burn from the fence while leaning on it to steady my camera for some pictures. The site was liberally posted with warning signs for high r.f. fields, for people wearing pacemakers.

Ya. I didn't think it had any thing to do with resonance. Just a mechanical shock wave - like hitting it with a hammer from a distance.

Well, perhaps not resonance in the usual high Q sense, but one can contrast the effect with a material that is transparent to the waves, pick RF or ultrasonic... and last time I hit a rock with a hammer it seemed to make a sound...  :D

Well, nvm... it's not a big deal.

             _-_-bear

Not the most fun experience that I ever had, but it works!  They knock you out during the process, so not painful then, but its not real enjoyable for a couple of days following the procedure.  Those particles remaining are not necessarily as small as grains of sand!   :o :'(

73,  Jack, W9GT

Jack said:
So I have heard. I've been told it the closest thing a man can feel that is similar to child birth. It beats the hell out of removing kidneystones percutaneously. You only get three chances there and then the kidney is dead.  :'(

I have had to do SAR on a couple of body worn devices and have been to the labs so I have some info.

The lab that we used was in the DC area. In the case of my devices, the antenna is actually attached to the body by taping it onto the skin.

The SAR limits are as mentioned, in mW per cm squared. To measure the SAR (Specific Absorption Rate), you first must simulate the human body tissue. This is done by mixing up some goop per government recipes. At this lab they had a sink made of non-RF absorbing plastic shaped like the human upper torso.

The goop is poured in to fill the form (like you are made creepy crawlers as a kid).

Next the UUT (Unit Under Test) is place near or in my case taped on the part of the body that it will be near on the bottom outside surface of the sink.   

Next a calibrated heat probe is centered over the part of the body of interest and the probe is inserted all the way to the bottom of the sink near the device. At this close depth, a robotic scan is initiated. The probe is withdrawn slightly and the scan is repeated. After a while a calibrated 3D heat profile is printed out and you clearly see how deep the RF is causing an effect.

In my case the devices exceeded the general public safety limits slightly, but were well within the occupational and professional limits (yes uncle has two limits and the public is protected by 10X).

It took a while to get a spot in the lab because the cell phone folks had it backed up. The object with a cell phone is to be JUST in spec - that is JUST under the limits. Otherwise you would complain that your cellphone did not work!

Mike WU2D