Setting exposure limits to anything potentially harmful is a legal and medical minefield. The best I ever hope for is guidance, not limits.
As George notes, some people have suffered significant harm from RF fields. Others, not at all. Remember, the microwave oven was "invented" by an engineer working around magnetron RF sources and discovered the "Hershey" chocolate bar in his shirt pocket had melted. When he figured out why, the "Radar Range" (first brand of microwave oven) was born. One cold night in the late 1950's, working outside on a flight line of F-86D fighters lined up wingtip to wingtip for preflight repairs and testing, I concluded I must be catching the flu. I felt weak hot and sweaty after several minutes talking with someone. We were standing in front of the planes, most of which had the nose radomes removed for testing the fire-control radar systems. Looking up, I noticed the radar antenna of one plane across the way with someone sitting in the cockpit was pointing directly at me. On a hunch, I took a few steps to one side and the antenna twitched to follow me. I immediately moved completely out of the way and within a short time I felt quite normal. Relating the experience to other people working the flight line, I learned it was a common occurance. The concept of being "cooked" by RF radiation was new and no one thought much of it. I don't think I, nor did I hear of anyone else, being injured by the experience, although I was thereafter careful not to stand in front of a transmitting radar antenna again. Not that Lockheed wasn't paying attention. We used to gather around the tailpipes on break after an engine run, occasionally roasting a hot dog or sausage on a stick held up just inside the afterburner which often still glowed red, and they quickly forbade that practice for safety reasons. But non-ionizing electromagnetic radiation was not on anyone's "radar" so to speak back then. 73, Ron AC7AC -----Original Message----- From: Elecraft [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Gmail - George Sent: Friday, April 7, 2017 12:55 PM To: elecraft@mailman.qth.net Subject: Re: [Elecraft] Was Amplifier - Now RF exposure limits Ed & Brian, My father had severe health consequences from working in a classroom with operating military radars! Since the adoption of OET 65 in the late 90s, all licensees (including Hams) have had the responsibility to insure their station is in complete compliance with RF exposure limit guidelines. Most likely during your last license renewal or application for a new license, you checked a box stating you would insure compliance with non-ionization radiation limits. Those guidelines are contained in bulletin OET 65. For Hams OET 65 Supplement B (https://transition.fcc.gov/bureaus/oet/info/documents/bulletins/oet65/oet65 b.pdf) gives us some shortcuts to insure compliance without the tedious calculations. Many of the tables were provided by ARRL & the W5YI Group. There are also calculators available on the internet to make it quite easy. Googleing "amateur radio oet 65 calculator" returned many to choose from. The only caveat I will give is that most of the shortcuts and calculators are for a single transmitting antenna at a specific location. Multiple radiating antenna WILL change the protection distances - Field Day & group contesting come to mind! Use to be we had to submit OET 65 compliance statements when licensing all transmitters for Broadcast Stations ranging from 150 MHz to 23 GHz. I believe we finally could use just a blanket cover statement ; but it has been a while since I licensed a non-Ham transmitter. You do need to insure you are in compliance - to protect your family, friends, neighbors and yourself. 73 George AI4VZ From: brian "Considered dangerous" isn't quite right. The jury is out of the exact danger levels of RF for all the various frequencies. These distances are more of an accepted limit that protects you from inquiries regarding RF exposure. Pointing to the distances being met helps get you off the hook. People will be surprised to see how small the distances these calculations are-- especially at lower frequencies. One note often overlooked. The distance is defined as the distance from feedpoint (usually center) of the antenna. Also the duty cycle can be considered in the calculation. There are stock duty cycles for SSB and CW given in the documentation. Antenna gain may have to be included. It used to be that anything at 100 watts and below at HF was exempted. I believe that has changed. 73 de Brian/K3KO On 4/7/2017 16:06 PM, Edward R Cole wrote: > In the USAmerica ham's now have the *responsibility* of determining > the safe operating zones for each antenna per FCC regulation. I doubt > many ever do the calculation. Fortunately Australian ham Doug > MacArthur (sk) VK3UM (a well known eme'r) has written a program which > you can download for free. I will simulate the emf fields base on > your input data like antenna, power, height, band and produces the > legal exclusion zones where RF exposure is considered dangerous. > > http://www.vk3um.com/emr%20calculator.html > > Its not hard to use and provides some interesting if not surprising > info about your station safety. > > As I already stated, it is the legal requirement for all US hams to > have evaluated safe range for humans before operating. > > Eg: half-wave dipole, 1400w, line loss 0.5 dB, 14.2 MHz: exclusion = > 3.06m radially; safe height 2.60m for FCC. Also provides ARPNSA and > CEU radiation limits. > > 73, Ed - KL7uW ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to r...@elecraft.com ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
