Electromagnetic hazards.

[460 0]

I've looked at somes articles and I cannot find an appreciable hazard to humans from an exposure to RF radiation. The effect on tissue from RF is heating, which can permanently damage the eyes and temporarily damage the testicles (but a hot bath can do worse). The radiation will become much more hazardous above about 10GHz, especially at 22GHz at a water resonance absorption frequency, and generally for higher frequencies. Fortunately, most towers do not radiate at such high frequencies. I suspect some of the communication dishes do however transmit at such high frequencies, since the directionality of the antenna increases with increasing frequency. These may pose a hazard to equipment and or humans. There was an incident years ago where a jumper's camera fried once while in freefall as he passed a comm dish. The comm dish provided fields strong enough to induce currents in the metal and semiconductor components, resulting in a damaged camera. Notice also the diameter of the waveguide. The waveguide dimensions are comparable to the wavelength of the radiation. A narrow waveguide will generally transmit a much higher frequency. A large waveguide will transmit a lower frequency. I think the real hazard is related to arcing and the subsequent production of x-rays. I believe a transmitter will arc to a person if they stand too close to it. Also, there may be arcing occuring inside the transmitter, which will produce x-rays. This may provide a significant hazard. Arcing will also produce ozone, which is noticable by its distinct sweet humid smell. Some people will say the fillings in your teeth will heat up, etc. This doesn't seem plausible if the surrounding metal is not hot. However, heating of metal on the body or rig and portions of the tower should occur if x-rays are being produced. X-rays will be much more readily absorbed by metal and dense tissue than normal flesh. X-rays are very directional and may be the inadvertant source of much of the urban legends surrounding the hazards of towers. AM towers are a different issue. The absorption of radiation by the body follows the dipole model. Essentially what this model says is that absorption occurs when the wavelength is comparable to the length of the body (or some rational fraction of the wavelength, up to some point). I don't know if hazards exist simply from the small amount of current that flows through the body while on an AM tower, or if the hazard originates from low energy x-rays. The x-ray theory is testable by taking unexposed camera film into various radio tower scenarios.

I do have some knowledge of x ray production by equipment that creates VHF and microwaves. X ray production can be a real hazard.

X-rays can originate from arcing and bremstralung or so-called braking radiation from the deacceleration of an electron impinging upon a metal target. Arcing can significantly damage hardware in some radiotransmission systems, and will also greatly increase noise of the transmitted signal. Some systems such as klystrons, twystrons, magnetrons, etc... use something called a crowbar when the transmitter (located on the ground, not the transmitting antenna or stinger) arcs to prevent such damage. Arcing should be uncommon and therefore x-ray production should be uncommon. Tthe power on most AM towers is much lower than a TV tower. The chance of arcing and hence x-ray production should be much, much lower for a low power AM system.

In case you are curious about the skin depth effect, I think the skin depth may be somewhat deeper than a few mm. See for example

http://speech.llnl.gov/thesis/3_2.htm

which quotes a few centimeters to a couple tens of centimeters based on tissue measurements of horses and pigs at microwave frequencies. This seems consistent with the behavior of food heating in a traditional microwave oven.

These are all opinions and are not definitive.

Looks like a death sandwich without the bread - Steve Deadman Morrell, BASE 174

[grundleson 0]

wow. thats quite a piece right there.
i know dishes heat you up and you dont want to get in front of them, the fillings in your mouth heat up and cameras do funny things. but it all makes more sense now.


-e

[base570 1]

Thanks for the information as always chris, you are an assett to our commintyI have often comes across situations where my camera shuts down or picks up the station being broadcast from the tower. It always comes at the worst times too!!
Jason
570

[NickDG 23]

There are studies done by both sides spinning the issue to suit themselves. One side comes out with a study that says people who live underneath high voltage power lines have more cancers. These studies are paid for by people who live under power lines.

Then a power company pays for a study that says it's not true.

The studies by Universities can go either way. However, most of these call for more study.

I'm convinced exposure to high amounts of EMR causes changes on the molecular level. No one, so far, has been definitive, but I think the fact we now live in a virtual sea of EMR is causing some problems for some people . . .

I know it's hard to stay away if you have a very convenient local tower that happens to be AM. But, my advice is stay away. We did AM a lot the early days of BASE and we justified it by thinking we weren't going to last long BASE jumping anyway. Now, we know that a career in BASE jumping isn't necessarily a death sentence.

If you love jumping towers, move to Florida, but even with the FM/TV towers always practice, Get On, Get Up, Get Off, as fast as possible . . .

NickD BASE 194

[base736 0]

Quote

I don't know if hazards exist simply from the small amount of current that flows through the body while on an AM tower, or if the hazard originates from low energy x-rays.

Due to the skin effect, high-frequency radiation (ie, anything over, say, a kilohertz -- definitely including AM) doesn't penetrate more than a millimeter or so. Only your epidermis knows you're on the antenna, as long as you're not grounded (which is the real danger on an AM antenna). Heat can spread from there, causing tissue heating as you noted.

If you're getting x-rays, though, then what you're climbing is definitely not an AM antenna. Or a communications tower of any kind. Maybe a death ray or something?

[460 0]

X-rays can originate from arcing and bremstralung or so-called braking radiation from the deacceleration of an electron impinging upon a metal target. Arcing can significantly damage hardware in some radiotransmission systems, and will also greatly increase noise of the transmitted signal. Some systems such as klystrons, twystrons, magnetrons, etc... use something called a crowbar when the transmitter (located on the ground, not the transmitting antenna or stinger) arcs to prevent such damage. Arcing should be uncommon and therefore x-ray production should be uncommon. Tthe power on most AM towers is much lower than a TV tower. The chance of arcing and hence x-ray production should be much, much lower for a low power AM system.


I think the skin depth may be somewhat deeper than a few mm. See for example

http://speech.llnl.gov/thesis/3_2.htm

which quotes a few centimeters to a couple tens of centimeters based on tissue measurements of horses and pigs at microwave frequencies. This seems consistent with the behavior of food heating in a traditional microwave oven.

Looks like a death sandwich without the bread - Steve Deadman Morrell, BASE 174

[base736 0]

Quote

I think the skin depth may be somewhat deeper than a few mm. See for example

http://speech.llnl.gov/thesis/3_2.htm

which quotes a few centimeters to a couple tens of centimeters based on tissue measurements of horses and pigs at microwave frequencies. This seems consistent with the behavior of food heating in a traditional microwave oven.

Cool! The sources I've seen quoted millimeters, and a quick calculation confirmed that; clearly I've missed something.

[veter_ 0]

Are there any radiation level detectors for AM/FM available to consumers?

While effects of radiation on humans is a controversial subject, relative level of radiation for different antennas (or different places on same antenna) is valuable data.

[truckerbase 0]

The article you analyzed also mentioned the effect of body heating on endocrinal homeostasis, resulting in a change in hormone levels in the body. Theoretically causing weight gain, mood shifts, and other tangible medical problems given long term exposure. Presumably minimal with an hours exposure (climb) and of temporary duration (until homeostasis is reacquired in body chemistry).

Also, with a background in electronics, I can say that "arc-ing" is one of the last things you want going on in an electronics environment, as this production is adverse both to signal integrity and mechanical longevity. Design should preclude significance. Tower equipment should not be doing this to any significant degree, or immediate service would be indicated. At least Navy equipment was designed where "arc-ing" was in no way a factor, and x-ray production from an electronic source was of so negligible an amount as to be unmentionable if not impossible. Most electronics with this kind of potential are shielded, to protect not only technicians but also circuits. EMF pulses will knock out electronics. Also, Electrical "arc-ing" produces bursts along the entire spectrum of electromagnetc energy, including heat and light and all ranges of Radiofrequency energy, including X-rays. X-Rays being only a small percentage of the energy budget produced, and the total energy produced by arc-ing would be dwarfed by the frequency that the equipment would be designed to emit. Hence maintaining that intended frequency as the primary hazard. Lastly any X-rays being produced by jumper proximity electronics would not only be in all frequencies but would also be omnidirectional in no way focused on the jumper: further reducing its adverse effects. Most heavy transmitting equipment is in the building at the base, not on the tower itself...soooo...

Anyway, thanks for the analysis of the article you posted long ago. Appreciated.

[460 0]

I overemphasized x-rays. Arcing is rare, hard on the equipment, and disrupts communications. Any x-ray production (which would depend on how the rf radiation is generated, i.e. like a magnetron with high energy electron bunches that are stopped on a metal target) would generally be confined to the transmitter module housed (and shielded) in a building. If equipment is arcing, it is generally malfunctioning. Tissue heating is the only issue that seems to be relevant. I don't understand how this could be very hazardous since our bodies can get extremely hot for extended periods with a high fever.

Looks like a death sandwich without the bread - Steve Deadman Morrell, BASE 174

[base736 0]

My understanding (from FAA stuff, which I expect you've already read) is that tissue heating of the type experienced by tower workers is hazardous only to the eyes and nuts. The effect on both (but certainly the second) was, as I recall, temporary.

A lot of people (not necessarily reliable) seem to make noise about this stuff causing cancer, but frankly I'm skeptical about mechanism. Covalent bond breaking (which tends to be the mechanism by which radiation causes cancer, as I understand it) just doesn't happen with RF/MW -- at least not without generating a plasma. Can anybody shed some light on this?