On Sat, 1 Jan 2005 11:34:16 -0700, "Rich" <nomore@spam.no> wrote:

>
>"Mike" <inundated9@yahoo.com> wrote in message
>news:57jdt0pmdffjmm2tfs29t8uimuusqqvege@4ax.com.. .
>> On Sat, 1 Jan 2005 09:59:22 -0500, "JoshIII"
>> <josh3iREMOVE@hotmail.com> wrote:
>>
>> >I have noticed the same thing with my GSM phone when hold it next to my
>> >computer speakers. My 800MHz CDMA phone doesn't make much if any
>> >interference like this. When you make a call with the 850+1900MHz GSM
>> >phone (Nokia 1100), the noise in the computer speakers is unbearable.
>>
>> I think you're right...it's GSM (and TDMA/iDen) vs. CDMA here, not the
>> frequency like the OP believes.
>
>Does GSM cause more harmful radiation than CDMA?
>
>
>>
>> I had the same problem with my then-Pacific Bell Wireless GSM phone
>> near speakers. (Pacific Bell Wireless has been absorbed into Cingular
>> in California and Nevada.)
>>
>> Mike

It is a curious thing that a radio device such as a cell phone can
cause interference to a non-radio device such as computer speakers,
conventional telephones, hi-fi systems, and even medical devices such
as hearing aids and pacemakers have reported problems. The cause is
not "harmful radiation", but rather a consequence of the type of
signal generation used by some (but not all) cell phone systems.

The type of interference can occur if the following things happen
together:
1) a pulsing radio transmitter,
2) with relatively strong power,
3) in very close proximity,
4) to a non-linear circuit element.

The non-linear circuit element is usually some sort of solid state
device such as a transistor or diode. If the non-linear element is
subjected to a strong pulsing radio signal, it will act as a rectifier
and "detect" the pulsating waveform, i.e., convert the pulsations from
a radio frequency to an audio frequency (if the pulsation rate is in
the pass-band of audio frequencies.) For example, a hearing aid
consists of a microphone, an audio amplifier and a small speaker. If
a strong pulsating radio signal impinges upon the first transistor
amplifier stage, the transistor will be driven into its non-linear
range and detect the pulsations. If the pulsation rate is in the
audio frequency range, the rest of the hearing aid amplifier will
amplify this and deliver it to the speaker, to the great annoyance of
the hearing aid wearer.

The above kinds of things were never reported with analog cell phones
because these phones use an FM waveform which is at a constant
strength, i.e., no pulsations. When the first GSM and TDMA phones
came into the consumer marketplace, such things began to be reported.
This happens because the fundamental waveform of these standards is a
pulsating waveform that has either a 1/8 or 1/3 duty cycle, depending
on which standard it is (also iDEN does this.) In the case of the US
TDMA (IS-136) standard, the pulsations occur at a 67 Hz rate. The
digital speech signals are gathered up over a 20 msec time interval
and then transmitted in two bursts of 3.33 msec. The rest of the time
(13.3 msec) other cell phones will transmit. Because the transmitter
is only on 1/3 of the time, it must transmit at 3 times the power
level that would be needed if continuous non-TDMA waveforms were being
used. In the case of GSM, the duty cycle is 1/8 and the burst rate is
a little over 200 Hz. Of course, the GSM signal has a peak power 8
times higher than the average power.

CDMA, on the other hand, when operating at the highest vocoder rate,
has a continuous waveform; i.e., no pulsating. Along with this, the
peak power and average power are equal. The average power is also
somewhat less than for GSM and IS-136 because of better modulation and
coding and much more accurate power control. Hence, one rarely hears
of people experiencing interference to non-radio type electronics with
CDMA cell phones.

If you're stuck with a GSM or TDMA phone, your alternatives to get rid
of this interference are pretty obvious - you eliminate one or more of
the 4 things required to cause the interference. The first two things
can be eliminated by switching to CDMA or trying to arrange to be
close to a base station so you won't be needing maximum power. The
third thing is to separate the cell phone from the victim of the
interference and the fourth thing is to replace the victim device with
a more interference withstanding device. Unfortunately, consumer
electronics are usually not designed with such interference rejection
capability in mind so there's not a lot that can be done. I suspect
that in the 12 years since TDMA systems were introduced that hearing
aids, pacemakers and the like have been redesigned with such
interference rejection in mind.

Good luck,
Klein