Posted: 6/18/2015 7:03:25 PM EDT
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In the thread about the new "Hi-power" HT's, Kekoa posted this question and I realized that even though I should know this, or know where to find it, I don't. Is there anyone who can point me towards more information about ERP and RF safety/limits?
Thanks in advance. (Apologies to Kekoa, seemed like a good topic for its own discussion) Quoted:
Quoted:
ETA: Back on topic, I wouldn't use an HT near my head with more than 5W... I like my eyeballs cool, and I don't like tissue heating. This is what I was going to say. I haven't researched it, so I don't know what the safe level is. And maybe I'm being overly cautious. But how many watts, of 440 MHz RF do you really want near your head? |
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RF Safety Calculator
I started looking at it, because my antennas are in the attic, about 10 feet above my head. I'm OK, but an 1500w amp is not in the near future. 
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ARRL page on RF safety
RF intensity calculator Acceptable levels are frequency dependent (makes sense, given how RF interacts with the large bags of water we are.) Per that calculator, a 8W 440 HT would be out of compliance if you were 1 foot away from a 1dB gain antenna. |
| FCC's guidelines, linked to from Kekoa's link Evaluating Compliance with FCC Guidelines for Human Exposure to Radiofrequency Electromagnetic Fields |
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Copying someone on another website.... Here is the complete list of Hams that have had will admit they have experienced health issues from RF exposure: fixed for you. My mom was a flight data recording nco in the airforce, on an airplane, right next to the recording racks, which were right next to the HF amplifiers. All tube. All leaky. She swears that she suffered reproductive harm by having to be next to the amplifiers all that time. Anecdotal, yes. But do you really believe that people stupid enough to ignore the guidance are going to admit that's what caused their cancer? |
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Quoted:
.... My mom was a flight data recording nco in the airforce, on an airplane, right next to the recording racks, which were right next to the HF amplifiers. All tube. All leaky. She swears that she suffered reproductive harm by having to be next to the amplifiers all that time. Quoted:
.... My mom was a flight data recording nco in the airforce, on an airplane, right next to the recording racks, which were right next to the HF amplifiers. All tube. All leaky. She swears that she suffered reproductive harm by having to be next to the amplifiers all that time. I'm going to leave that one alone!%@@! 
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But do you really believe that people stupid enough to ignore the guidance are going to admit that's what caused their cancer? Sure - this is litigious America - hence the deluge of phony lawsuits re cellphone cancer, cellphone causing gas pumps to explode, overhead power lines causing aliens to attack, etc.... Bottom line is: decades of study, tens of millions of users, gajillions of hours spent in close proximity to RF fields - and exactly zero cases of harm (at ERP levels Hams can generate). I know you'll find this shocking, but what we have here is a case of bureaucrats trying to justify their existence by sensationalizing, then pretending to fix a problem that doesn't exist with a bunch of non-scientifically supported rules. . . You have to worry about burning out your computer speakers LONG before you have to worry about exposure to HF/VHF fields. OTH, close exposure to multi-tens of KW ERP at UHF and above, and now your in the region where you begin to need to worry about exposure. |
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FWIW my job has had me around fairly high E-fields quite often at frequencies from HF to millimeter wave.
It takes a lot to make it a problem in the HF to UHF range because the standards specify a 6 minute average or even sometimes a 30 minute average. At the duty cycles associated with ham communications of any type it would be difficult to exceed the Maximum Permissible Exposure (MPE) under all but the most extreme circumstances. For instance, consider a 10dB gain antenna at 29MHz with 1500W input to the antenna running a digital mode or RTTY at 50% TX/RX duty cycle. That's about as bad as it's going to get for an HF scenario. Even with those numbers the limit for an uncontrolled environment is going to be a mere 90'. And that's before you consider any elevation pattern effects, which in general will make it perfectly safe for that antenna to be on the roof of the house. For additional reference military regulations are laid out here: http://www.dtic.mil/whs/directives/corres/pdf/605511p.pdf Those now reference the IEEE standard which can be found here: http://emfguide.itu.int/pdfs/C95.1-2005.pdf |
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Who's the Uniden guru at RR? Anyway, he loves to claim that there is no point in making a GMRS HT with an output rating of more than 2.5W because of SAR numbers in Part 2 for body worn transmitters (within 8 inches of the body). However, if you continue to read said SAR guidelines it gives the 6 minute time span. If you know how a Watt is derived (as in the SI unit) then you know that 2.5W at over a 6 minute interval is 2.5W @ continuous duty (i.e. 900 J). From that you can derive that 4W at 38% duty still fits that rating, 8W at 19% duty will still fit that rating. Most handhelds are designed for transmitting a 5-10% duty…
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