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Author Topic: Calculating radiated energy  (Read 1059 times)
VK2HLG
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Posts: 12




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« on: January 06, 2012, 09:28:52 PM »

Hello. This is my first post after a year of lurking.

My wife, kind and generally excellent though she is, is a worrier. Anything that might have an adverse health effect, however obscure, is a big concern for her.

So, when she found out that when I am sometimes running 20m WSPR at 5 or 10 watts overnight on my G5RV dipole (about 40 feet above ground, about 30 feet above and perpendicular to the roof of our one-story house), she objected, claiming a radiation hazard.

I told her that the two nearby TV towers (both about 2km away) are surely blasting more energy into us than my WSPR experiment. I didn't say it, but I am sure our IEEE 802.11n (Wi-Fi) router is, also.

How can I prove this? She is a scientist and would listen to real calculations. She won't believe, "There are no reported cases..."

Thanks.

Dave
VK2HLG
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W6RMK
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Posts: 656




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« Reply #1 on: January 06, 2012, 09:48:07 PM »

FCC OET Bulletin 65 (google for it) has a lot of stuff.

Ultimately, IEEE/ANSI C65.1 has what your wife wants to see.  The recommended limits are in there, and 100 pages of summaries of the literature and reams of journal citations.

For actual field levels.. you can do an approximation based on far field, or you can fire up NEC and do a better calculation.  But, realistically, at your power level, you can do a "worst case" kind of calculation and see that at a few meters away, there's no way you can exceed the limits.

The lowest limit is on the order of 1mW/sqcm (HF has higher limits). The area of a 1 meter radius sphere is 125,000 sq cm.  40 W will be 0.3 mW/sq cm at 1 meter.
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WB6BYU
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Posts: 13334




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« Reply #2 on: January 06, 2012, 10:16:27 PM »

802.11n wireless signals typically operate at around +16dBm output, or 30 - 40 mW. 
They might crank up to +20dBm (100mW) worst case when signal strengths are
poor.

The strongest signal strengths most folks are exposed to are when they operate a
mobile phone because the antenna is very close to their head.

The FCC requires all US hams to perform an RF exposure audit - that's the FCC
bulletin that was quoted earlier.  There are online calculators for this  That's not
to say that it is a perfect implementation that will allay all fears while ensuring
100% safety, but it gives you a starting point for your analysis.
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VK2FXXX
Member

Posts: 102




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« Reply #3 on: January 07, 2012, 12:43:55 AM »

Gday Dave

You could start here
http://www.acma.gov.au/WEB/STANDARD/pc=PC_1826

http://www.aic.gov.au/en/publications/previous%20series/proceedings/1-27/~/media/publications/proceedings/18/joyner.pdf

the full standard
http://www.arpansa.gov.au/pubs/rps/rps3.pdf

This introduction
http://www.leishman-associates.com.au/arps2009/downloads/presentations/ACRBR%20Stream%2027%20Oct%20-%20Vitas%20Anderson.pdf

to this
http://www.acma.gov.au/ExclusionZoneCalculator/Default.aspx


there is the numbers she requests!


Good luck ;]
Brendan
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WX7G
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Posts: 6129




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« Reply #4 on: January 07, 2012, 08:03:28 AM »

The E and H fields and energy density from your installation are way below the U.S. allowed levels. At your power level one is not required to run calculations.
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W5DXP
Member

Posts: 3613


WWW

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« Reply #5 on: January 07, 2012, 08:09:09 AM »

At your power level one is not required to run calculations.

Except by irrational XYLs. Smiley
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
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