Practical way for partial blocking of radio wave

Oct 17, 2007 6 Replies

I live in an area where the only Internet access I can get is through my mobile phone provider's (Sprint) EVDO network. I use a D-link Kyocera KR1 EVDO router to get Internet access through my computer (CAT5 cable from router to computer).



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Because my apartment is so small, the only practical place to position the KR1 is on a shelf about 18 inches away from my head. I know that long-term exposure to cell phone radiation is probably harmless to me, but I think the KR1 puts out a much stronger signal than a cell phone.



I'm wondering, does it sound practical to place a 6" x 10" piece of cardboard covered in aluminum foil about 1 inch from the KR1, in between the KR1 and my head, with the purpose of interfering with the radio waves (blocking them?) in that particular direction?



I believe my Internet access would be unaffected, because the KR1 would still more than 75% of a "sphere of radiation" to propagate its signal.



Would such a setup potentially "block" radio waves in the way that I'm thinking? (Or have the waves already messed up my thinking?)



Thanks in advance.



Ask your landlord about an external antenna. Or, at those freq's/power levels, you could probably mount a directional antenna indoors (closet?) and point it at the tower.

Good Luck! Rich

Tin foil hats are common in SED, and that is regardless of radio waves.

The human body is not resonant at 2.4 GHz, to power transfer will be extremely low. There is no evidence to suggest cellular harm by anything other than tissue heating, which will not happen with the power level this device broadcasts.

Also, I would bet putting an "external antenna" on the device will violate FCC Rules. (and it may not work any better either). So, why bother.?

Metal in the near field of the antenna will scatter (not "block") RF Fields. Where (and how) it scatters affects both absorbed RF (which is going to be a tiny, tiny fraction anyway), and more importantly, could cause detrimental multipath to the OFDM signal. Your best bet is to leave several inches unobstructed all the way around, and even below and on top of, the devices antenna(s).

Lastly, the FCC's website has a decent write-up on Radiofrequency Radiation Safety if you're interested. There'll be a link on the main site, or you can Google the FCC's Office of Engineering & Technology (OET) to locate the RF Safety pages. But in short, you do not have a problem with RF levels. Not even close. -mpm

Here's the relevant RF Safety page at the FCC web site:

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Equation 3 on Page 19 of the document is the simplified approach to your question. Because the power is low, and it's divided by the square of the distance, the power density rolls off in a big hurry. Plus, the RF losses due to non-resonance at 2.4 GHz are enormous.

But I'll still be exposed to the (relatively-more-powerful-than-a-cell- phone's) radio waves.

Would aluminum block those waves in the way I've described?

I don't know that the energy would necessarily be more powerful. The cell phone uplink power is controlled by the cellular base station, and that will vary according to lots of factors that vary moment-to-moment - and too numerous to get into here.

The same is true of the router. Where each is in respect to the other at any given instant in time is impossible to say with any certainty. However, even at continuous max output power, neither device is going to present a problem. Off hand, I'd say they each represent less than

0.0001% of the allowable standard. (And that might be if you actually licked the antenna!)

As to your other question, aluminum foil will scatter the incident radio wave. If you were to construct a "shield", you could expect a reduction of energy behind the "shield". But again, the reduction is inconsequential, because the energy levels are inconsequential in the first place.

Now, having said that, I can tell you I've been involved in many tower site zoning hearings where this exact sort of question comes up -- only in those instances, the power levels are MUCH higher and actually do present a hazard. (at least to the tower climbers and antenna repair personnel). They are much closer to the high-power side of this situation....

I fully understand that some individuals remain unconvinced by the "evidence" that there is no detrimental effects attributable to low- levels of non-ionizing radiofrequency radiation. Other than certain rare forms of cancer (lukemia) that have a higher than expected incidence near 60 Hz high tension wires (likely, a much different problem than RF), I believe the evidence and research is very, very solid that chronic exposure to low-level RF is not a problem.

ANSI Standard C95.3 (IEEE) provides a good bibliography if you want to review the research.

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