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Discussion in 'The Lounge' started by TSGB, Nov 30, 2006.

  1. TSGB

    TSGB 1 ton status

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    What's the lowdown on RF hazards from your typical every-day devices? Cell phones, walkie talkies, and whatnot? The talkies I just got from Radio Shanty had a warning about how to keep it away from your head... :yikes:
     
  2. chevyfumes

    chevyfumes Court jester

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    Watch for the muzzleflash!
    Thats what tin foil hats are for stoopid...
     
  3. chalet2506

    chalet2506 1/2 ton status Premium Member

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    If rf waves do cause a problem, I don't think keeping the device away from your head is going to help. It's not like those things transmit in one direction or the transmission loses that much strength in the 30" from outstretched arm to your head. It's like duck and cover for an atomic blast. Makes people feel like they're doing something to protect themselves, but they're still just as well off kissing their ass goodbye.
     
  4. newyorkin

    newyorkin 1 ton status

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    Jagged should be able to throw some info in here, too, he builds and experiments with antennas, so I'm betting he knows way more than me about RF safety... I'm required to pass an RF safety course annually, but it's pretty easy.

    Consumer devices are generally pretty safe. Most consumer devices operate in milliwatts to single-digit watts, so the safe-distance from the antenna is usually a few cm to a foot. Ever see the big thick plastic antennas on cordless phones? The antenna is actually a wire inside that plastic thing, the plastic is a sheath to make sure nothing can get unsafely close to the antenna.

    Here's the book-sized post to explain it a little:

    RF radiation is non-ionizing, meaning it doesn't permenantly alter the molecules it affects. But your body does convert RF energy to heat, and since RF can go through just about anything, it can theoretically cook you from the inside out, similar to the old myth of a microwave oven cooking food in the center. The RF doesn't cause instantaneous permenant damage, but a continuos period of exposure will cause cell damage from the heat buildup. Part of RF safety awareness is timing your exposure to certain antennas and getting away from them for cooling periods. I saw a label somewhere that said "2 minutes on, 3 minutes off", meaning work near it for 2, get away from it for 3 to let your body cool. RF exposure has different symptoms for different people. For my boss, it makes him need to take a leak, even if he's dry. For me, it makes me very sleepy and headached.

    A Microwave oven is an RF transmitter that's concentrating RF energy into the food to cook it. Because it's non-ionizing, it doesn't change the molecular structure of the food other than how the heat alters it, so you can eat it as if you cooked it under radiant heat.

    Distance form the antenna is actually very important. Radio Frequency energy attenuates (loses strength) over distance, so the further you are from the transmitting antenna, the less the RF will affect you. If you're right on top of the antenna, such as holding the phone to your head, you may have bio-cells (skin/brain/bone/blood/etc) in a zone that's only considered safe for xx minutes.

    The FCC mandated modern cell phones to be safe for continuos exposure for some crazy long period of time, but old cell phones just had a warning label in the manual, which no one ever read, and they were found after several years to be pretty dangerous the way people were using them. I know a guy with brain tumors who used to constantly be on his cell phone during the 90's. Even though I know RF is not supposed to cause permenant damage, I don't doubt the cell phone's transmitter made a huge contribution to brain cells turning cancerous.

    Your 2-way is probably safe to have near your head while transmitting for a few seconds, but it depends on the power. The label is probably generic, to avoid being too complicated for people to understand. It might even be an FCC required label now.
    If it's a strong tx with some power, it wouldn't be a good idea to keep it too close to your head for a long time. But guys have been using fairly powerful two-way handhelds that they have to hold near their mouth to talk/transmit anyway, and most of them are ok...

    The key is the antenna more than the device (the RF should be internally contained up to the antenna). The antenna is what pushes out the RF, so if you're using an external antenna and all you have near your head is a piece of coax, you should be fine.

    These Bluetooth things worry me a little cause they're constantly on a persons head. I don't know anything about Bluetooth, it's frequencies, if the tx is always on, or what. But with an omnidirectional antenna to get to your phone which I think they say can be 30 feet away, it's not as powerful a transmitter as your cell phone, which may need to go miles...

    That was a nice quick answer...:doah: :wink1:
     
  5. randy88k5

    randy88k5 1/2 ton status

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    Just a little elaboration on the point made here. RFs cause atoms and molecules to vibrate. The vibration and speed of these molecules is the definition of heat.

    Microwave ovens used a magnitron which puts out a frequency that matches a resonant frequency for water molecules. Near resonance, a small input can lead to a large output. (Takoma Narrows bridge, breaking step crossing a bridge, trampoline, etc...)

    Also, light (all forms, including RF) intensity is inversely proportional to the square of the distance. IE ... the father the source is from you, the less intesity it has.

    With that being said, I do not believe the myth about (consumer) cell phones and the like. It does not affect my cell phone usage one bit.
     
  6. readymix

    readymix 3/4 ton status

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    The danger is NILL from anything you could buy at the store.

    Even a CB putting out 4 watts won't hurt you for a few reasons. The 4W is what comes out of the radio, but the V/M measurement would be way less. As stated before they are omni-directional.

    Now look at my CB setup which will light a 40W fluorescent bulb from about 10 feet away from the antenna......Still not really gonna do any damage. Mainly because it is still relatively low power and non-ionizing RF.

    Still the non-I RF could still hurt. Like standing in front of one of my Weapons Radars would boil the fluid in your body in a few seconds and cause 3rd degree RF burns. They put out FAR more RF energy than anything you will likely ever get your hands on.
     
  7. Jagged

    Jagged 1 ton status

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    As has been said. The only way RF affects your body is heating it up. However, there are two critical areas of your body that cannot dissipate heat as fast as the rest of your body. Your eyes, and your testicles.

    Also, like has been said, RF density pretty much follows an inverse logarithmic pattern as you increase distance from the antenna.

    Here's a short list of minum antenna distance required in a controlled environment (as in you are using the radio, controlling your exposure)

    29.7 MHz (CB, and some radio control devices):
    100 Watts (more than 25 times legal CB output) -- 4.6 feet

    50 MHz (other radio control devices):
    50 Watts -- 3.3 feet

    1240 MHz (around cell phone frequency IIRC)
    50 Watts -- 1.6 feet


    Keep in mind, these limits are for an ideal, 1/2 wavelength antenna. (Your cell phone antenna GMRS/etc antennas are not ideal). Also, most cell phones operate at under 1 watt of power. Most handheld radios are below 5 watts.





    I once burned myself with 200 watts of RF at 7.0 MHz. I was trying to adjust an indoor antenna for my HF radio, and knocked something over. My microphone was on VOX (voice activated), so the radio keyed up because of the noise... sending 200 watts through my finger. I got a burn similar to what you would get touching a car's cigarette lighter while hot.
     
  8. newyorkin

    newyorkin 1 ton status

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    Thanks for the correction and elaboration, fellas. :thumb: :thumb: :waytogo:
     
  9. TSGB

    TSGB 1 ton status

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    Thest are the exact type of answers I was looking for! Detailed, but not over my head. I appreciate the time and knowledge! :waytogo:

    Galloping Girdy, as we say in the TaComa area... :D
     

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