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Author Topic: RF safe distance  (Read 4408 times)
KK4IKO
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Posts: 67




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« on: June 02, 2012, 07:14:02 AM »

I'm building the portable 2m yagi in the June issue of QST.  I plan to mount it 10-12' above the ground next to my vehicle (Jeep Cherokee) on the opposite side of the vehicle from my operating position (sitting down next to the vehicle under a canopy).  My radio is restricted to 50W on VHF.  Is there any danger from RF at that distance?  The antenna will be hand rotatable, but not during transmission.  If I read Table B in the RF Safety section of the handbook correctly, this does not seem to be a problem.

Thanks.

73
Bruce, KK4IKO
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K1CJS
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Posts: 6034




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« Reply #1 on: June 02, 2012, 08:08:17 AM »

For VHF frequencies, there is NO danger at any distance, but of course now, if you insist on touching the antenna while transmitting....   Grin

The dangers of RF have been way overblown.  Some people have their homes within spittin' distance of 50,000 watt AM transmitters, and there is not one report of ill health on the books directly attributed to that exposure.  Ditto on quite a few TV band transmitters.

You really don't have to worry about RF radiation until the frequencies get up into the 440 mhz range--and even then there is little danger.  Now, on the other hand, you're working even higher frequencies, 800 mhz into the gigahertz range,  you do have to start worrying about RF exposure.  2 meter VHF at fifty watts poses no risk to anyone.
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W5FYI
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« Reply #2 on: June 02, 2012, 10:53:08 AM »

It appears you are OK. It wouldn't hurt to go to http://www.arrl.org/files/file/Technology/tis/info/pdf/rfex1_2.pdf, print out Worksheet A on page 2, and fill in the form, in case anyone asks if you have complied with the FCC's exposure rules. If you have a log, you can annotate in it the date you did the evaluation.

Although I've never known anyone to experience RF exposure complications, I do know there is a movement to caution cell phone users of unnecessary exposure, and to opt out of wireless utilities metering. And contrary to what some people may think about the safety of VHF frequencies, the reason the evaluation is for 50 watts and above on those bands, and much higher on frequencies above and below VHF, is because the government thinks VHF is riskier than the other bands. It is sometimes cited that tall people approach resonance in the 2-meter band, where a full wavelength in the human conductor is in the vicinity of six feet!
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KB4QAA
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Posts: 2367




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« Reply #3 on: June 02, 2012, 11:33:44 AM »

At VHF and mid to lower UHF, the main effect on the body is generalized heating.

At upper UHF into SHF, the risk of cataracts of the cornea develops.

For that reason I recommend not standing directly in front or behind a V/U gain antenna with running any significant power.

No reason to dive to the deck or get in a panic for short exposures, just applying an abundance of caution. 
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K0YHV
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Posts: 179




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« Reply #4 on: June 02, 2012, 01:47:30 PM »

Just build the antenna, use it and have fun. Life it too short to worry about problems that don't exist.
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K1CJS
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« Reply #5 on: June 02, 2012, 02:19:57 PM »

The one and only reason that the government has set 'exposure standards' is that this society that we live in is a sue and get sued society.  "There is the danger..."  "The government says...." and so on is only scare tactics for general insurance purposes.  In other words, if someone does develop cancer and points to a ham antenna/transmitter as the cause, the government can say "See!  We told you so." 

The truth of the matter is that there have been HF, VHF and UHF RF transmissions all around us for years,and absolutely nothing has happened that is directly attributable to those transmissions.  Those that say there are are the same ones that believe the call "The sky is falling..."
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K4SAV
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« Reply #6 on: June 03, 2012, 06:54:25 AM »

There are rules for limiting RF exposure that amateur radio operators have to follow.  I suggest you follow them and avoid recommendations by the amateur health experts.
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K1CJS
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« Reply #7 on: June 03, 2012, 07:53:35 AM »

There are rules for limiting RF exposure that amateur radio operators have to follow.  I suggest you follow them and avoid recommendations by the amateur health experts.

Jerry, the only rule is that a form be filled out if an antenna is close to a residence or building and the power level is over a set amount.  IOW, mother government is trying to protect you.  The fact of the matter is that there is absolutely no proof that VHF RF hurts you in any way.  Police and fire units have been running radios in their cars for all too many years, and there is not one report where the people who rode in those cars have been affected in any way.

What K0YHV saids is true--
"Just build the antenna, use it and have fun. Life it too short to worry about problems that don't exist."

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KB1GMX
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« Reply #8 on: June 03, 2012, 08:14:19 AM »

Do the RF evaluation.  Its a worthwhile exercise. 

You will find there is no issue for several reasons.

Your antenna is many feet higher and you are not in the primary beam and at 50W
you are only approaching threshold power anyway.

If it were an issue you would then know the max power or added height needed.

It's not stupid rule or the sky is falling, it's taking due care to understand and know.
The likelihood of risk is very low, but having done the evaluation you have ground
to stand on and say based on 0ET-65 there is no issue.  That simple.


Allison
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K4SAV
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Posts: 1840




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« Reply #9 on: June 03, 2012, 11:02:16 AM »

Jerry, the only rule is that a form be filled out if an antenna is close to a residence or building and the power level is over a set amount.  IOW, mother government is trying to protect you.  The fact of the matter is that there is absolutely no proof that VHF RF hurts you in any way.  

Here are the rules that must be followed.
http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/oet65b.pdf

Your opinion of what is safe or not (or that of any other ham for that matter) is irrelevant.  We have many rules we must follow as hams.  They are not optional.  You can't run 5KW either just because you want to and you happen to have an amp that will do it.  Abide by the rules.

Jerry, K4SAV
« Last Edit: June 03, 2012, 11:11:59 AM by K4SAV » Logged
KB4QAA
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Posts: 2367




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« Reply #10 on: June 03, 2012, 12:33:57 PM »

As long as no one else is involved, you can do anything you want with your equipment including testing for voltage with your tongue, hanging yourself with coax, and getting that perfect RF tan in front of your full legal limit gain antennas.

Again, the key points are:

-There is no proof that RF causes cellular mutations or cancer
-There is no reason for fear of RF at the level's authorized to hams
-Do some 'what if' calculations so you get a feel for what 'recommended safe' levels are for your equipment
-Take reasonable precautions to limit your RF exposure
-If RF was incredibly dangerous or curative, Radiomen, technicians and hams would either be the sickest or the healthiest people on earth.  They are neither.
-Don't worry, be happy.
« Last Edit: June 03, 2012, 12:37:46 PM by KB4QAA » Logged
KK4IKO
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Posts: 67




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« Reply #11 on: June 04, 2012, 04:39:23 AM »

Thanks all, for the information.

Not to sound like a smart @&*, but I wasn't looking for dissertations on the possible effects of RF exposure pro or con...I already know, having been an electrical/electronics technician all my working life (now retired).  I was just asking for knowledgeable opinions about exposure to a specific antenna in an area where there will be other people wandering around, which I certainly got from several folks.

The consensus seems to be that it won't be an issue if set up and used as described.

Bruce, KK4IKO
« Last Edit: June 04, 2012, 04:42:33 AM by KK4IKO » Logged
KG4NEL
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Posts: 373




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« Reply #12 on: June 04, 2012, 10:47:18 AM »

Thanks all, for the information.

Not to sound like a smart @&*, but I wasn't looking for dissertations on the possible effects of RF exposure pro or con...I already know, having been an electrical/electronics technician all my working life (now retired).  I was just asking for knowledgeable opinions about exposure to a specific antenna in an area where there will be other people wandering around, which I certainly got from several folks.

The consensus seems to be that it won't be an issue if set up and used as described.

Bruce, KK4IKO

When making a power/antenna change, I like to enter the parameters into this calculator: http://hintlink.com/power_density.htm

Sure, the FCC white paper is the one to refer to, but reading that in its entirety reminds me of 8AM calc classes I'm glad I finished with. Something to be said for a quick "go/no go" check. And I haven't been BBQ'ed yet. Cheesy
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K1CJS
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« Reply #13 on: June 04, 2012, 06:26:17 PM »

At least you've got one thing right.  You can't run 5 KW--because the regs limit you to 1.5 KW. 
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