In article <(E-Mail Removed)>,
(E-Mail Removed)
says...
> Alan Gauton wrote:
> > In article <(E-Mail Removed) >,
> > (E-Mail Removed) says...
> >
> >>I have a Planex 802.11b adapter that I bought in Japan. I live in the US...
> >>
> >>I can pick Africa, Asia, Europe... and also Japan and US....
> >>
> >>What's up with that? Are there different 802.11b standards for each
> >>'region'? Could my japanese CF card be looking for a Japanese AP????
> >
> >
> > Nope, there aren't different standards for 802.11b - what there is is a
> > difference in the part of the radio spectrum allowed for traffic. The
> > regulators in different countries restrict areas for commercial use,
> > emergency services, etc.
> >
>
> OK, so where can I find out about this? I assume that some regions also
> allow greater signal strength than others...
>
> Any details available?
Maybe not the best reply, but Wikipedia gives this:
Channels and international compatibility
802.11b and 802.11g divide the spectrum into 14 overlapping, staggered
channels whose center frequencies are 5 megahertz (MHz) apart. It is a
common misconception that channels 1, 6 and 11 (and, if available in the
regulatory domain, channel 14) do not overlap and those channels (or
other sets with similar gaps) can be used so that multiple networks can
operate in close proximity without interfering with each other, but this
statement is somewhat over-simplified. The 802.11b and 802.11g standards
do not specify the width of a channel; rather, they specify the center
frequency of the channel and a spectral mask for that channel. The
spectral mask for 802.11b requires that the signal be attenuated by at
least 30 dB from its peak energy at ±11 MHz from the center frequency,
and attenuated by at least 50 dB from its peak energy at ±22 MHz from
the center frequency.
Since the spectral mask only defines power output restrictions up to ±22
MHz from the center frequency, it is often assumed that the energy of
the channel extends no further than these limits. In reality, if the
transmitter is sufficiently powerful, the signal can be quite strong
even beyond the ±22 MHz point. Therefore, it is incorrect to say that
channels 1, 6, and 11 do not overlap. It is more correct to say that,
given the separation between channels 1, 6, and 11, the signal on any
channel should be sufficiently attenuated to minimally interfere with a
transmitter on any other channel. However, this is not universally true;
for example, a powerful transmitter on channel 1 can easily overwhelm a
weaker transmitter on channel 6. In one lab test, throughput on a file
transfer on channel 11 decreased slightly when a similar transfer began
on channel 1, indicating that even channels 1 and 11 can interfere with
each other to some extent.
Although the statement that channels 1, 6, and 11 are "non-overlapping"
is incomplete, the 1, 6, 11 guideline has merit. If transmitters are
closer together than channels 1, 6, and 11 (e.g. 1, 4, 7, and 10),
overlap between the channels will probably cause unacceptable
degradation of signal quality and throughput.
The channels that are available for use in a particular country differ
according to the regulations of that country. In the United States, for
example, FCC regulations only allow channels 1 through 11 to be used. In
Europe channels 1-13 are licensed for 802.11b operation but allow lower
transmitted power (only 100mW) to reduce the interference with other ISM
band users.
--
AG
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Alan Gauton E-Mail agauton @ postmaster.co.uk
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(Damon Hill - 16th June 1999)
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