Hey Chuck-

The first of the two sources that you have linked below seems to contain
misleading, inaccurate information. My first tip as an RF Engineering
Student was the claim that you can "increase the effiency of your
antenna". They claim that "The increase gain can be from 3dB (100%
increase in signal strength) to 9dB (400% increase)."

The first part of this statement is accurate: 3dB increase in signal
strength, in general, is *about* double the gain. (3dB = 10 *
Log10(1.99526) and 1.99526 is about 2, or twice the gain.) The second
part, however, is inaccurate. 9dB = 10* Log10(7.94328) or about a gain of
8, not 400% or 4. This means that a one-watt signal would effectively be 8
watts, not 4 watts. This means that our friend mis-calculated something or
didn't get his calculator out at all when creating the web page.

Perhaps the most tell-tale sign that something is amiss when I am reading
web sites on the internet is when I see statements like:

"Without getting into the  physics of why it does not work,..."

Whether the device does or does not work doesn't seem more apparent then
the accusations on the web page, and the tests done by the author seem to
lack any technical detail.

The second link is interesting, as it comes from the Federal Trade
Comission. I always looked to the FTC for consumer advice on products,
until now. The FTC claims that:

"According to the FTC, there is no scientific proof that the so-called
shields significantly reduce exposure from electromagnetic emissions."

Perhaps this is true, given the current-day consumer-sold RF shields. But
that is not to say that we can't create RF shields. The real problem is
that consumers want small size, and don't want ugly antennas getting in
their way of cell phone usage.

Do cell-phones cause cancer? Dr. Dean-Edell last night on the radio
dispelled this common belief. There is no scientific evidence either way.
Perhaps my RF engineering professor put it best:

In the early days of cell phones in Europe, heavy users of early 1 and
5-watt cellphones complained of getting headaches after using the phones
for an extended period of time. After some experimentation by the
goverment, Europe set it's limit at 1 Watt for hand-held phones with
radiators next to your head. In the USA, the FCC set that limit at .5
watts. As a result, most of your cellphones radiate 450 mW = .450 Watts.

The FCC also sets the safe RF exposure limits for humans. According to the
assignment that we recently handed in, located at:

   http://www.ece.umn.edu/class/ee4601/4601F02Ass3.pdf

(see problem 3) The FCC says the safe exposure limits at 2.2 Ghz in a
24-hour period are 2mW/cm^2. Let's take my cellphone, a voicestream phone,
for example:

I have a 1.9 Ghz phone, like most other digital phones. The Professor
estimated that about 1/3 of the power from the cellphone is disappeated
into my head as I use it. That's 450 mW /3 = 150 mW. The antenna on my
phone spans the entire length of the phone casing, but I will discount
that for now and only talk about the external antenna. The external
antenna is 3cm tall by about 1 cm wide. This is 3cm*1cm = 3cm^2.

Roughly, I am disappating 150mW/3cm^2 or 50mW/cm^2 into my head. If I can
assume that the FCC's guidelines for 2.2 Ghz are close to that of 1.9 Ghz
(since they are close in frequency) then I have exceeded the 2mW/cm^2
exposure limit if I use my cellphone for a 24-hour period.

But then again, the batteries on my cellphone only last 2 hours max. So, I
am exposed to 50mW/cm^2 of power for 2 hours, where the safe limit is
based on a 24-hour period. If I only use my phone 2 hours a day before the
battery dies I believe I will come just above the daily exposure
guideline.

I apologise now for getting all technical and stuff here, but I have seen
some things go by on the list as of recent that are completely off-base
and I haven't had time to reply to all of them until now.

Regards,
---Matthew Genelin---



> Jeff asked where I saw these notices, so I thought others might enjoy
the references...
>
> Fraudulent cell phone antenna boosters described here:
> http://cellantenna.com/internal_cell_phone_antenna.htm
>
> also sold with similarly fraudulent "radiation shields":
> http://www.ftc.gov/bcp/conline/pubs/alerts/cellshlds.htm
>
> I'm not sure that the ad I saw for lead-lined jeans was a joke... might
have been a product for sale!  Be careful!  The power output of a
typical wireless card or cell phone is much more than a million times the
natural radiation around "sensitive parts", so maybe TCWUG should make
some public service announcements...
>
>
>
> ---
> Chuck
>
>
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