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Author Topic: Dangers of an indoor antenna.  (Read 13180 times)
KD2BDG
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Posts: 16




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« on: February 26, 2012, 03:04:17 PM »

I have an indoor antenna. Its a slim jim-jpole antenna. It's made of 450 ohm twin ladder lead cable. I was told by someone today that it is extremely dangerous to have this hanging next to my window at the power I was using. I use 20 watts on low and 45 on high power. he told me to move it outdoors unless I want to develop cancer. Is this true?
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WB6BYU
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Posts: 13484




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« Reply #1 on: February 26, 2012, 03:24:59 PM »

How will you know for sure unless you use it for 40 years to find out?

The FCC has RF exposure guidelines, and all licensees are expected to analyze our stations
against them.  There are calculators on the web that will step you through the process.

The guidelines are for the protection of others, not the operator.

The links between RF radiation and cancer are disputed.  There are other ways it can
damage humans, especially in the UHF range.  (Consider the microwave oven, for example.)
Whether or not it is a problem in your case depends on the frequency, power level, and the
distance between you and the antenna when you are transmitting.

Personally I have a 440 ground plane hanging from a suction cup on the inside of the window
by my desk.  I might think twice about running it on high power, but I leave at 5 watts because
it works well enough.  If you need 20 or 45 watts then it may be worthwhile improving the
antenna regardless of the risk from RF exposure, and getting it outside is one way to do that.
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LB5KE
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Posts: 141




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« Reply #2 on: February 26, 2012, 04:39:36 PM »

Also, I think a 5watt handheld will produce just as much or more RF.
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AC5UP
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Posts: 3927




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« Reply #3 on: February 26, 2012, 05:23:03 PM »

I was told by someone today that it is extremely dangerous to have this hanging next to my window at the power I was using.

Six years ago I had a Melanoma excised. Went through adjuvant radiation and interferon therapies to increase my odds of making cancer a one-time event and the important part of that first sentence is "six years ago". This probably means I'll live long enough to die from heart disease. I've had some lovely sunburns in my youth and most likely one of them encouraged the Melanoma 20 - 25 years later. Or, might not be related at all, but it was quite a coincidence I had a Squamous Cell Carcinoma a few inches away from Ol' Mel and both are allegedly caused by too much sunlight. Point being that almost everything you do today will affect you in some way down the road and some of those effects can be life-altering. Your job today is to figure out which ones you'll regret later if you ignore them...........

If I knew then what I know now I'd have avoided those sunburns and that oddly-shaped dark spot would have been removed muy pronto.

Run the minimum power needed for a reliable contact. Not only could you be saving yourself some grief down the road but you'll also be operating in the spirit of Part 97. I have no doubt there will be comments from folks who are 100% sure RF exposure carries no health risk. You know... Like back when cigarette smoking was so safe that most doctors smoked unfiltered Camels.   Tongue

http://wellmedicated.com/lists/40-gorgeous-vintage-tobacco-advertisements/
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K0ZN
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Posts: 1560




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« Reply #4 on: February 26, 2012, 05:40:56 PM »


 You never indicated what frequencies and how far away from the antenna you are at the operating position.  There are guidelines available.  440 MHz is where you
 do need to be concerned.  "Some" concern on 2 M.

 Give more specific and detailed information.

73,  K0ZN
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KD2BDG
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Posts: 16




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« Reply #5 on: February 26, 2012, 05:51:08 PM »

Ok, yea Im operating 2m only and the antenna is only 5 or 6 feet from my desk. Would an attic antenna be a better choice? I can't really put one outside right now.
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K0ZN
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Posts: 1560




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« Reply #6 on: February 27, 2012, 09:22:48 PM »

 
Without going into a lot of details.... Yes, at 4 or 5 ft., you are probably too close to the antenna. Personally, if I was that close to a 2 M antenna, I would
keep the power pretty low.  Attic would be much better as you would be well below the main radiation pattern.  Worst place is broadside to the antenna.  The "Best" place is directly above or below it.

73,  K0ZN
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VA7CPC
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Posts: 2406




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« Reply #7 on: February 27, 2012, 11:58:45 PM »

Why rely on our guesses?  Run your numbers through an RF-exposure calculator!   One is here:

http://www.eham.net/articles/24456

There's a _long_ article about E/M field dangers on the ARRL website:

http://www.arrl.org/rf-radiation-and-electromagnetic-field-safety

You'll be better off learning what the issues are, and doing your own calculations and making your own decisions about the dangers.

                Charles

PS -- I don't know if anyone has asked, but:

. . . How many hours per day are you actually transmitting? 
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ONAIR
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Posts: 1747




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« Reply #8 on: February 28, 2012, 12:07:37 AM »

Ok, yea Im operating 2m only and the antenna is only 5 or 6 feet from my desk. Would an attic antenna be a better choice? I can't really put one outside right now.
  Wouldn't hurt to be on the safe side and put it in the attic if you can, and it might even work better!  Otherwise, I would just try to relocate the indoor antenna a greater distance away from your desk.
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KB4QAA
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Posts: 2450




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« Reply #9 on: February 28, 2012, 03:49:25 AM »

There are no consistent scientific studies that have ever shown a cause-effect relationship between RF and cancer.

RF causes general tissue heating, but does not cause genetic changes which result in cancer.  The biggest dangers come at VHF and above where corneal damage (cataracts) result from high exposure.

The FCC set RF standards based on an abundance of caution but no proof of any real danger based on the recommendations of the IEEE and other organizations.

In summary, having a VHF antenna inside, by  a window is not a specific hazard.  Don't sit next to it if you are running high power.   I would always avoid sitting in front or behind a directional gain antenna like a yagi or quad which essentially multiplies the exposure.

Don't worry, be happy.  Radio has been in use for over a century.  Millions radio operators and technicians have spent whole careers bathed in RF without danger.  Smiley   b.
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N6AJR
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Posts: 9921




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« Reply #10 on: February 28, 2012, 10:56:57 AM »

We stick a cell phone as close to our brain as possible, ( a cell phone is really a 900  mhz transceiver) and we talk on a HT at 5 watts, again next to our heads,  so 10 or 40 watts at some 10 or 15 feet is not something I would worry about.

 Reminds me  of the brother of my old  neighbor. He would come out and visit for a month at a time.  Every morning he would run a couple of laps around the block for his health.  One day he was doing his morning run, had a heart attack and died, bang, But boy was he healthy when he died.

the point is to take care and use reasonable precautions, buttttttttttttttttt throw some common sense  in the deal too.
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W0BTU
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« Reply #11 on: February 29, 2012, 05:42:51 AM »

There are no consistent scientific studies that have ever shown a cause-effect relationship between RF and cancer. ... The FCC set RF standards based on an abundance of caution but no proof ... Radio has been in use for over a century.  Millions radio operators and technicians have spent whole careers bathed in RF without danger.  Smiley   b.

Right on. Couldn't possibly have said it any better myself.

Have you noticed the absolute lack of any real-life examples of harm to anyone, anywhere, from being near the high-power RF field of an antenna at HF? (Or for that matter, at any frequency?)

I've talked to people who spent their lives making their living in the field of an HF antenna IN THE ERP MEGAWATT RANGE.

Point us to just ONE proven example of someone getting harmed by RF from an antenna below 30 MHz
, and I'll reconsider.

This 'danger from HF radiation' hype is simply utter nonsense.
« Last Edit: March 02, 2012, 06:25:19 PM by W0BTU » Logged

WX7G
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Posts: 6213




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« Reply #12 on: February 29, 2012, 05:52:31 AM »

An RF safety calculator shows that you are on the edge of safe/unsafe given 45 watts, antenna 5 dBi, 6 feet distance, 146 MHz. Change the distance to 5 feet and you are no longer safe.

http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=11352
« Last Edit: February 29, 2012, 05:55:47 AM by WX7G » Logged
W6RMK
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Posts: 662




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« Reply #13 on: March 02, 2012, 03:23:41 PM »

146 MHz = a bit more than 2 meter wavelength.  6 feet away is only two wavelengths..

All those online calculators use "far field approximation"   (that is, they convert to an Effective Isotropic Radiated Power, and assume a point source) and a couple wavelengths away isn't "far field"..  The division between far and near field is a fuzzy one, but in general, one likes to say "several wavelengths" to be sure. (and don't get confused by  the term "far field" used in antenna range measurements: the 2*D^2/lambda criteria.. that's not relevant here.. that's where a "plane wave approximation" is valid)..

The problem with the near field is that there are antennas with very large near field energies (compact HF loops are notorious) even if their gain is terrible in the far field.  You have to look at the actual magnetic and electric fields to determine whether you are within the limits.

Another notorious problem is being close to the bottom of a HF vertical on low bands.  Wavelength is 40 or 80 meters, and most of the time, the antenna is sitting your backyard, and most people's backyards aren't 80 meters or 160 meters long.

OET bulletin 65 gives you some "safe harbor" calculations for things, and if you happen to exactly match one of their canned solutions, then you've met the legal requirement.  They've actually gone out and measured/modeled the near and far fields and generated the tables accordingly.

Do anything else, and you're on the hook to do a real analysis (or find someone who can).
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WB6BYU
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Posts: 13484




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« Reply #14 on: March 02, 2012, 04:37:14 PM »

Quote from: W6RMK

146 MHz = a bit more than 2 meter wavelength.  6 feet away is only two wavelengths..



Just under 1 wavelength, actually.
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