Subject: (Curry) Re Modulated signals (or pulsed???) (fwd)
Date: Wed, 13 Jan 1999 131752 -0600 (CST)
From: "Roy L. Beavers" <rbeavers@llion.org>
To: emfguru <rbeavers@llion.org>
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---------- Forwarded message ----------
Date: Wed, 13 Jan 1999 12:40:35 -0700
From: "Bill P. Curry"
To: "Roy L. Beavers"
Subject: Re: Modulated signals (or pulsed???)
Roy,
I would like to inquire of your readers whether anyone knows whether the
fodulation technique for cell phones is amplitude modulation or frequency
modulation. I am ignorant on this score. If the carrier wave is amplitude
modulated at audio frequencies, then I think the situation resembles the case
of the digital PCS phones, which employ pulses at a pulse repitition
frequency near 200 Hz.
I think the significance of this is the following: 1) Experiments
carried out (I think) at Columbia University have investigated a range of
frequencies to determine sensitivity of bioeffects caused by sinusoidal
EMR to frequency.
As I recall, the range investigated was from 0 to several thousand Hz, but the
range of greatest sensitivity was from 0 - 500 Hz. Note that the pulsing rate
of digital PCS phones is around 200 Hz and well within the frequency range of
greatest sensitivity. 2) Since cell phones are not high fidelity audio
devices, the range of audio modulation frequencies i n cell phone
transmissions is probably about 40 Hz to 8,000 Hz. (A high fidelity audio
system would be about 20 Hz to 20,000 Hz - slightly beyond the range of human
hearing.) Thus, amplitude modulation at the audio frequencies also covers the
range at which there is sensitivity of bioeffects to EMR. 3) By Fourier's
theorem, any complex wave form - whether it be a rectangular pulse or an audio
modulated signal - can be decomposed into an infinite number of sine waves,
each of which has a particular frequency and a particular amplitude. Because
the majority of information in this expansion is carried by relatively few
terms in the Fourier series, the infinite series effectively becomes a finite
series - one with relatively few sinusoidal terms (This is the principle on
which the Fast Fourier Transform method of analyzing dynamical response fo a
system is based.) Thus, either a series of pulses or an audio modulated
carrier wave will be equivalent to a number of sine waves (of different
amplitudes) whose frequencies cover the range in which bioeffects have been
found to be most likely.
If, on the other hand, cell phones use frequncy modulation, instead of
amplitude modulation, then I don't know how to analyze the situation, but I
speculate that bioeffects would be less likely than with amplitude modulation
(assuming there is also no pulsing). I would like to see yours and your
readers' comments on this.
----
Bill P. Curry, Ph.D. |Physics is fun.
EMSciTek Consulting Co. |Trying to make a living!
22W101 McCarron Road, |Phone: (630) 858-9377
Glen Ellyn, IL 60137 |Fax: same, but require prior notice
Home page: http://www.EMSciTek.com
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Reprinted with permission of Roy Beavers, http://www.feb.se/EMF-L/EMF-L.html