From: "Ed Price"
Subject: Re: Cell phone emissions
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Fri, 11 Oct 2002 08:39:34 GMT
NNTP-Posting-Date: Fri, 11 Oct 2002 04:39:34 EDT
Organization: Cox Communications
"carltons" wrote in message
> In article , "Ed Price"
> > "News2020" wrote in message
> > news:firstname.lastname@example.org...
> > >
> > > No. At the point of skin contact, the energy seems to be significant.
> > >
> > > "Ken Taylor" wrote in message
> > > news:ao2q8a$in39d$1@ID-76636.news.dfncis.de...
> > > > "News2020" wrote in message
> > > > news:Cv5p9.email@example.com...
> > > > >
> > > > > I just did a quick/rough calculation.
> > > > >
> > > > > Comparing a microwave oven to a cell phone in power.
> > > > >
> > > > > A 0.3 Watt cell phone flush with the skin would be approaching
> > kind
> > > > of
> > > > > density ?
> > > > >
> > > > Approaching what, that you were inside the oven??
> > Show us your numbers.
> > Ed
> Hi Guys,
> I joined this thread kind of late, but my contribution is that I measured
> a microwave oven in our engineering lab at one meter in front of the door
> with a vertical dipole tuned for 2.5 GHz and measured 20 dBm. The oven
> was one of those low power small jobs, but that gives you some idea about
> the ovens anyway. I hope it helps. Also, Dr Q Balzano at Motorola did
> extensive measurements of cell phone power effects and concluded that the
> emissions were non-harmful to humans. I guess that someone, somewhere,
> will disagree, but they probably don't have the evidence that Dr Q does
> and are probably shooting from the hip.
> BTW, Did anyone consider near-field versus far-field, VSWR, etc. ?
> Antenna return loss is not so good when the antenna is placed against
> someone's face, for example. This problem is extremely complicated as far
> as engineering goes, but it is further complicated by the emotional
> aspects of the discussion. I would really hate to be given this problem
> to solve as I won't know how to resolve it completely. I'll leave that to
> the PhD's and others who are a lot smarter than me.
> Please don't bother to flame me. This is just, after all, my opinion with
> some hard data included. :-)
> Steve Carlton
> Plantation, FL
As I suspected, we won't be able to discuss your observations very well,
because there's a big level of suspicion right from the start. Now this
isn't a flame; we're talking about non-ionizing radiation. Since you are a
college-level engineering student, you should be able to easily handle the
I assume your used a typical spectrum analyzer, with a 50 Ohm input
impedance, to measure your reported 20 dBm. Wow! This is a high level at the
analyzer; I wouldn't allow my analyzer to see +20 dBm at its input. I would
use attenuators to bring the input power down to a maximum of 0 dBm.
Anyway, let's get the units adjusted to those typically used in emission
measurements. +20 dBm (in a 50 Ohm system) is +127 dBuV. If we assume you
used a good coax cable, the loss at 2.45 GHz might be about 5 dB. So that
means a voltage out of the antenna of +132 dBuV.
Now things get messy. A dipole antenna isn't normally used to measure field
strengths above about 1 GHz; horns are more accurate. I couldn't find an
example of a calibrated, commercially available, 2.45 GHz dipole antenna.
So, I'm assuming you made your own antenna. A dipole would have a
theoretical antenna factor of about 32 dB at 2.45 GHz. (A home-made dipole
is anybody's guess, but it likely would not be better, so 32 dB could be
used as a minimum.) So, that +132 dBuV at the antenna output corresponds to
a field strength of +164 dBuV, or +44 dBV, or about 160 V/M at the
measurement antenna position.
160 V/M is one helluva field; I spend tens of kilobucks to generate fields
like that for military testing. I can guarantee you, based on personal
experience, that you can feel the heating effect from a 160 V/M field at 2
GHz. Since you didn't report feeling any heating effect, I have to assume
that you did NOT have a 160 V/M field. So that means something is wrong
somewhere. Is the analyzer calibrated? Are you sure you didn't read +20 dBuV
instead of +20 dBm? (That alone would be a 107 dB error.)
In the USA (and other places), microwave ovens are limited to a maximum
leakage of 5 mW/cm sq at a distance of 5 cm from the oven surface. At 1
meter (20 times greater distance), a 5 mW/cm sq field would decay to 1/400,
or 12.5 uW/cm sq. (OK, 5 cm is NOT far-field, so we can't extrapolate
perfectly, but you tell me what factor to use.) Even a decay to 1/100 would
be 50 uW/cm sq. And that would be undetectable to a typical Hand-held Narda
or Holaday exposure meter. (The 160 V/M field that you thought you had is
equivalent to a power density of about 68 W/ m sq, or 6.8 mW/cm sq.)
Before you can work on tough problems, like tissue absorption and energy
reflection off tissue layers and thermal conductivity of bodily fluids, you
have to have mastered microwave field measurement technique. And since
microwave measurements always disturb the field as you try to measure it,
you have to cross-check all your observations to guard against polluted
data. You can't get anywhere trying to base a line of inquiry on outrageous