VHF - Maximum Permissible Exposure

[18rabbit]

Some folks here might be interested in this… I just got off the phone with the EM people at Underwriters Laboratory about VHF radiation and its (controversial) effects on human tissue. What occurs is the VHF transmission frequency is an ideal wavelength to penetrate and vibrate cells in the human body. The vibration action heats the cells such that we are slowly cooking ourselves. No one knows the long-term affect of this VHF bar-b-que so the FCC has established guidelines to limit the cumulative exposure. When a product does not test within FCC regulations, the manufacturer puts the responsibility for compliance on the installation, where corrections for the product’s shortcomings have to be made. (Note: VHF radiates through the antenna so how the receiver could ever be made to comply is beyond me.)<br /><br />I ran into this issue while pre-reading the manuals of VHF radios prior to purchasing a radio. I decided on an ICOM IC-M602 with a Shakespeare 6db gain antenna. ICOM mentions that a 9db gain antenna needs to be at least 5-ft away from everyone at all times or metal shielding in place to protect people from VHF radiation. We can’t get 5-ft away, about 2-ft at most, so we need to install the shielding. Obviously, we aren’t shielding the antenna, or it would be an antenna anymore. The directionality of the antenna could become an issue if the transmission beam is focused at people. Our antenna will be located overhead, vertically so this shouldn’t be a concern. It was suggested a grounded foil or even metal mesh as large and simple as chicken wire, installed across the top of the cabin is all that is needed. We will install a metal mesh before reinstalling the cabin headliner.<br /><br />1w, 3w, and 5w, handheld VHF radios are worth rethinking if this issue is important to you. They are powerful enough and they radiate right into your head, but to an unknown total affect. It is a similar issue to the cell phone controversy. That was mentioned also, and yes, from what I was just told cell phones are a source of brain cell damage, but again, the long-term affect is not known. Maybe it doesn’t matter. Could go either way. (Does this imply I have extra brain cells? And can I wire them for immediate use? ) The person I spoke with seemed to think a lot of the cell phone controversy is motivated more by politics than actual science. There is also some controversy with the VHF as well. The person at UL looked up the references for the actual frequencies and suggested it may not be a bad idea to go ahead protecting against them.<br /><br />Has anyone on this forum done anything to address this with your VHF radio/antenna?

 

[burp]

Re: VHF - Maximum Permissible Exposure

18rabbit, Not to alarm you but you are constantly being blasted by RF energy, from TV/radio stations, CB/Ham radios, cell phones, radar, garage door openers and who know what else. Ever had an MRI (magnetic resonance imaging) exam? They use RF pulses to disturb the resonating hydrogen molecules in your body to produce the images.<br /><br />I wouldn't loose too much sleep over shielding your VHF antenna unless you live under the antenna and are transmitting constantly at high power. In an emergency I'd rather be radiated a little bit than limit my transmission range.

 

[Boatist]

Re: VHF - Maximum Permissible Exposure

Rabbit<br />If worried about it then get a 6 DB antenna and mount it up on the cab with a 4 foot extension. The 6 and 9 DB antennas have a very low and narrow radiation pattern. This will put you out of any radiation pattern unless your standing on a 10 latter in the back of the boat. Lots of testing on this in ham radios and Cell phones. The jury still out. Cell phones probably the worst since they are held with the antenna right against the head. Both VHF ham radios and VHF marine the radio is held in front of you and antenna goes above the head. VHF ham Handheld raido's are limited to 7 watt because of this fact.

 

[18rabbit]

Re: VHF - Maximum Permissible Exposure

Burp – I am aware there is a lot of stray radiation whipping thru every corner of this planet from man, earth and solar. If only you could only see what’s in the kitchen when you turn on the microwave oven. That said, I still don’t put my head into the microwave while it’s cooking...unless there’s a bag of popcorn in there… You’re right about infreq VHF exposure.<br /><br />Boatist – what you said is pretty much in line with what UL said. Cell phones xmit in milliwatts (500-600mw) and handheld VHF is up to 5w. The affect (if any) is thought to be cumulative, cell use results in much more exposure, but at a different freq. The actual xmit frequency (in MHz) is their concern. Cells are up there at 824-894 and 1850-1990 while VHF is down in the 100-200 (156-163 for marine use). It was suggested that shielding from the lower VHF freq. was a good idea, shielding from cell's freq. is political. ?!?!? I have no experience with any of this.<br /><br />Fwiw: Radar is a whole different matter. I knew it was dangerous to watch while cooking. UL said the units used on commercial cargo ships have actually fried birds that flew in front of function radar. I got a mental image of a bunch a salty dogs tossing a Thanksgiving turkey up into the radar beam to cook their holiday dinner.

 

[snapperbait]

Re: VHF - Maximum Permissible Exposure

Radar is great for making popcorn...

 

[mattttt25]

Re: VHF - Maximum Permissible Exposure

should see what the radars we use in the navy can do. i've seen plenty of birds go down hard after flying by when active. also lost a $600 camcorder in about 2 seconds of standing to close to a SPY transmitter. fun stuff.

 

[waterinthefuel]

Re: VHF - Maximum Permissible Exposure

Dude, unless you transmit on high power while getting very intimate with your antenna you have nothing to worry about. The food you eat while out on the water will kill you faster than your VHF radio! LOL

 

[ThomWV]

Re: VHF - Maximum Permissible Exposure

This is almost laughable.<br /><br />Let's start with the easy part. Where is your antenna? Not that 8-foot-tall white shaft that's bolted to the hardtop or console side, I mean the real antenna, the radiating element? Easy, its a chunk of wire, or mabe a rod of brass, that is about 18 inches long and held firmly in the very tip top of that white tube we call the antenna. So if the thing is 8 feet long and pointing up there's a built in 6 and a half feet distance right there. If the base of the antenna is on the hard top then its all shooting 8 or 10 feet over your head anyway.<br /><br />Now, how much power are we talking about here? Folks, its 25 watts. That happens to be the wattage that is often used in the bulbs in a refridgerator or oven. Immagine that intensity of light, or energy in any other form, shining on your arm for an hour ... just immagine all the damage its doing to your person .... NOT!<br /><br />At any rate the FCC, not Underwriter's Laboratorys (which is in fact a good source of information, just not the best one for this purpose) sets the standards here. I know they publish tables for how close a person might be exposed to RF energy from different types of antennas at diffeent frequencys of different powers. I don't recall ever seeing one for a 2-meger dipole antenna of anything less than 50 or 100 watts. They may exist, and that would be the final word on how safe it is (there's no commercial value in this regulatory function of the FCC so it hasn't been deregulated and thrown in the trash just yet). They were in the study guides when I got my HAM license, but I gave all those books away to some folks who were studying to get their tickets.<br /><br />Thom<br />KC8NID

 

[18rabbit]

Re: VHF - Maximum Permissible Exposure

I’ll take an independent lab’s standard over that of a gov’t agency’s any day. Reference; the allowable exposure to microwave oven radiation in the US is about 1000 time more than the allowable limit set in the USSR. My brain’s attempt at logic tells me the safe limit is probably somewhere between the two.<br /><br />A lot of the standards set by the FCC, FAA presume a ‘normal’ exposure over an average lifetime. You need look no further than the gov’t recommendations for consuming the fish you caught. Here’s something that should bring the value of those standards into focus:<br /><br />A few years back we experienced a huge influx of migration from the Pacific Rim and an associated increase of fish consumption. As a result, the gov’t decided it should re-evaluate the mercury levels in fish caught in the SF bay. I had an opportunity to meet with a biologist contracted to do some of the testing. He tested every consumable part, the fillet, the skin, the fins, eyeballs…everything that is normally consumed in the Asia cultures. His tests were immediately tossed and he was admonished to test only the fillet, the part that has the least concentration of mercury. He argued the skin has a much higher concentration of mercury and should be considered because it is frequently consumed by all cultures. “Nope! Don’t want to hear it. Test only the fillet.” Thom – there’s your gov’t (not ind. lab’s) “final word on how safe it is.” <br /><br />Most folks don’t have an idea of how extensive testing at UL is or how often it is repeated and re-evaluated. I doubt there is a single piece of wire or plastic on the face of this planet that is not manufactured and/or labeled to UL standards.<br /><br />UL’s issue is with the marine VHF frequency, not refrigerator light bulbs. Different frequencies have different effects. While the 25w light bulb may not be an issue with your arm, exposure to a 25w microwave source for an hour is going to have a different result. Wattage?…if you know where the bird is, effective satellite communications with consumer products requires as little as 3w.<br /><br />The marine VHF frequency is tuned to your body’s tissues. There is no question that it is doing accumulative damage, whatever the wattage. The only question is how much damage over how long a period should be considered safe. And for that, I’m going with the independent lab’s recommendations.

 

[ThomWV]

Re: VHF - Maximum Permissible Exposure

No its not. It might be argued that microwaves are somehow mystically "tuned" to your body, but that's about as close as you could come. This is a 2 meter wavelength were taling about here, about as benign as a TV broadcast signal.<br /><br />And where on earth do you think you're beloved UL got the standards they use? The FCC of today is not the FCC that put together a realistic set of scientifically derived performance and safety standards in the 50's and 60's, the hayday of American radio.<br /><br />Anyway you're warnings nice but unnecessary. I have no idea why you'd want to scare people away from what is easily the most important safety device they can have on the boat, and particularly when you consider that if the radio's being used properly it won't be outputting any power at all for more than mere minutes on the hour out of any trip. I mean, how much are you guys using your radios to talk? I might go 10 trips and never key the mike on mine. There's no radiation in receiving, so lets get away from anything that might make a person leary of buying this, the most important thing you can have next to PFD's.<br /><br />Thom

 

[18rabbit]

Re: VHF - Maximum Permissible Exposure

From page iii of the ICOM IC-M602 VHF marine transceiver instruction manual:<br /><br />RADIO OPERATOR WARNING<br /><br />Icom requires the radio operator to meet the<br />FCC Requirements for Radio Frequency Exposure.<br />An omnidirectional antenna with gain not<br />greater than 9 dBi must be mounted a minimum<br />of 5 meters (measured from the lowest point of<br />the antenna) vertically above the main deck and all possible<br />personnel. This is the minimum safe separation distance estimated<br />to meet all RF exposure compliance requirements. This<br />5 meter distance is based on the FCC Safe Maximum Permissible<br />Exposure (MPE) distance of 3 meters added to the<br />height of an adult (2 meters) and is appropriate for all vessels.<br />For watercraft without suitable structures, the antenna must<br />be mounted so as to maintain a minimum of 1 meter vertically<br />between the antenna, (measured from the lowest point of the<br />antenna), to the heads of all persons AND all persons must<br />stay outside of the 3 meter MPE radius.<br />Do not transmit with radio and antenna when persons are<br />within the MPE radius of the antenna, unless such persons<br />(such as driver or radio operator) are shielded from antenna<br />field by a grounded metallic barrier. The MPE Radius is the<br />minimum distance from the antenna axis that person should<br />maintain in order to avoid RF exposure higher than the allowable<br />MPE level set by FCC.<br /><br />FAILURE TO OBSERVE THESE LIMITS MAY ALLOW<br />THOSE WITHIN THE MPE RADIUS TO EXPERIENCE RF<br />RADIATION ABSORPTION WHICH EXCEEDS THE FCC<br />MAXIMUM PERMISSIBLE EXPOSURE (MPE) LIMIT.<br />IT IS THE RESPONSIBILITY OF THE RADIO OPERATOR<br />TO ENSURE THAT THE MAXIMUM PERMISSIBLE EXPOSURE<br />LIMITS ARE OBSERVED AT ALL TIMES DURING<br />RADIO TRANSMISSION. THE RADIO OPERATOR IS TO<br />ENSURE THAT NO BYSTANDERS COME WITHIN THE<br />RADIUS OF THE MAXIMUM PERMISSIBLE EXPOSURE<br />LIMITS.<br />Determining MPE Radius<br />THE MAXIMUM PERMISSIBLE EXPOSURE (MPE) RADIUS<br />HAS BEEN ESTIMATED TO BE A RADIUS OF<br />ABOUT 3M PER OET BULLETIN 65 OF THE FCC.<br />THIS ESTIMATE IS MADE ASSUMING THE MAXIMUM<br />POWER OF THE RADIO AND ANTENNAS WITH A MAXIMUM<br />GAIN OF 9dBi ARE USED FOR A SHIP MOUNTED<br />SYSTEM.

 

[waterinthefuel]

Re: VHF - Maximum Permissible Exposure

Look man, do you have a cell phone? If you do the radiation from the antenna a half inch from your head is doing more damage than your seldomly used VHF. <br /><br />Don't worry, just go fishing and have fun.