Subject: Re Qualcom cellphone (fwd)
Date: Fri, 20 Feb 1998 004220 -0600 (CST)
From: "Roy L. Beavers" <rbeavers@llion.org>
To: emfguru@hotmail.com
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---------- Forwarded message ----------
Date: Fri, 20 Feb 1998 12:39:38 +1100
From: Stewart Fist
To: "Roy L. Beavers"
Subject: Re: Qualcom cellphone (fwd)
I know that Bertha thinks that I am being disloyal, and out to 'get' her
in some way. But I'm not. I just think we need to get our information
right.
Antenna and aerial are the same. One is a British term and the other an American.
It doesn't matter (from a manufacturers viewpoint) whether the R/F radiating
element is within the plastic case, or external. The decision is probably
made mainly on the basis (in the early days) of the expectation of the
customer, and later, on the need for compact size.
The length of the antenna/aerial element is a mathematical relationship with
the frequency being used, so at cell phone frequencies (longer wavelengths)
the radiating element needs to be longer than at PCS frequencies. One of the
advantages of PCS over cellular is that the hand-helds can be made smaller
since all parts of the radio-frequency stage are dealing with wavelengths that
are roughly half the size (8-900MHz as against 1.8-1.9GHz).
Qualcomm phones can often operate in both analog and digital systems (called
dual-mode) but these modulation systems aren't linked to frequency.
So the QCP-800 dual-mode phone from Qualcomm operates in both analog and
digital format at 800MHz, because it contains both the CDMA system of
modulation/demodulation (called Code Division because it is a peculiar form of
digital) and AMPS which is the old FM analog form of modulation/demodulation.
Qualcomm also make a PCS digital handset, the QCP-1900 which operates in
digital-only at the higher PCS frequencies of 1.9GHz.
The characteristics which probably distinguish CDMA digital systems from other
forms of digital, is that they use less power and don't pulse the power they
do output. In fact, CDMA generally operates at a lower output power than AMPS
— but since power output of a handset is under control of the base-station,
this is a pretty meaningless claim in any cellphone system. However CDMA
alone of all radio systems is capable of operating at power levels so low that
the signal can't be easily distinguished from background radio noise.
This is why it was kept secret for so long. It was a valuable tool for the
military because not only couldn't the enemy decipher the transmissions, they
often couldn't detect that transmission was taking place.
Which is not to say that CDMA phones aren't a potential problem up against the
side of the head, because here they are obviously putting out R/F power, even
though probably at a slightly lower level than AMPS, and much less than the
peak power of TDMA/GSM systems.
The confusion of CDMA PCS with Qualcomm's satellite system (called Globalstar)
is another problem. Globalstar operates on quite different frequencies
(1.6GHz and 2.5GHz) to both PCS and the cellphone dual-modes. Eventually
someone may build a dual-mode PCS/satellite handset, but I've not heard of any
attempts yet, and I suspect that there will not be in the immediate future,
simply because PCS is designed to transmit over distances of a mile or so,
while Globalsta must reach out 1414kms, at the closest — and be able to punch
through the atmosphere over much longer distances as the satellites pass from
the horizon, to overhead.
There will be very significant power differences here, so satellite handsets
could well produce a power problem.
However each Globalstar satellite is powered by a solar panel producing 1100
Watts, which is the power of a single-bar electric radiator. This drives all
the control and receiving electronics, and the transmitter also. The signal
output power is about 500 Watts, which is the power of my front garden light.
This power is beamed over 1400 kms, and spreads over a continental area
"several thousand kilometers in diameter", which means at a minimum, a million
square kilometers.
The chance of you getting sunburnt from a garden lamp at 1400 kms, spreading
its light over a million square kilometers, is rather remote. As is the
chance of you getting a brain tumor from such a device beaming radio signals
at a slightly lower frequency than the light.
So while there is a legitmate worry about GSM and TDMA cellphone handsets
against the side of the head, I fail to see why we need to panic about
satellites.
When we do, we are rightly seen as irrational, and rejected in legitimate
scientific and political circles as panic-mongerers.
This diverts attention away from the real potential problems of handsets, held
in close proximity to the head.
--
Stewart Fist - technical writer and columnist
See: http://www.australian.aust.com/computer/cmpcols.htm
http://www.abc.net.au/http/sfist/ (some archives)
http://www.electric-words.com (main archives)
Archive provided courtesy of WaveGuide, http://www.wave-guide.org
Reprinted with permission of Roy Beavers, http://www.feb.se/EMF-L/EMF-L.html