On 2007-05-03, Klay Anderson <klay@klay.com> wrote:
> In article <16mj33hsi82mlmnac0q90rju1q1l76rn08@4ax.com>,
> karlkrandall@sbcglobal.net wrote:
>
>> Just means your radio or PC speakers are likely junk from China
>> and not adequately shielded. Not Cingular's fault at all.
>
> No no no. Look, a cell phone is a two-way radio running somewhere in
> the 800-1900 mHz band. This means it transmits and receives. The radio
> waves emitted by a GSM handset can have a peak power of 2 watts, and a
> US analog phone had a maximum transmit power of 3.6 watts. Other digital
> mobile technologies, such as CDMA and TDMA, use lower output power,
> typically below 1 watt.

That's not quite right. All digital phones seem to run about the
same average output power these days, about 0.2-0.3 Watts. GSM
phones may actually be on the lower end of this judging by how
long a charge in their teeny tiny batteries tends to last. The
thing about TDMA phones (i.e. TDMA, GSM and Nextel) is that they
transmit in short bursts, being quiet most of the time and then spitting
out a narrow-band signal over a short period. To have an average power
of, say, 0.25W, when you are only transmitting 1/8th of the time
the peak power needs to be a lot higher, but the average is still
the same as, say, a CDMA phone which transmits continuously when
connected.

The problem with all these TDMA phones is that the bursts themselves
tend to be transmitted at audio frequencies, i.e. a burst every
few milliseconds. It doesn't take much to demodulate this into
something you can hear, and while the remaining audio frequency
power is tiny if it gets into the front of an amplifier section
it can, as you say, be amplified a lot. It is still a fault of
the electronics that it is receiving this stuff (it is obviously
possible to design circuits resistant to this; the phones themselves
don't usually interfere with their own audio) but the nature of the
signal makes this more difficult.

The thing I wanted to point out, however, is that this isn't
limited to GSM phones. I've heard Nextel phones doing it too, and
I suspect TDMA phones probably did it as well. I think it is
inherent to the technology.

Dennis Ferguson