[kismac] Re: Wireless Link
- From: Brad Knowles <brad.knowles@xxxxxxxxx>
- To: kismac@xxxxxxxxxxxxx
- Date: Mon, 17 May 2004 10:09:54 +0200
At 8:52 AM +0100 2004/05/17, Ian Beeby wrote:
In many administrations, there is a fixed maximum effective radiated
power for 802.11 systems, and this is calculated by taking the power
output of the transmitter, subtracting the feeder and connector loss
and adding the antenna gain.
Keep in mind that this varies greatly by country, region, etc....
If you don't know what the EIRP limits are in your area, before you
go playing around with high-gain antennas you should talk to local
ham radio operators and experienced wireless network operators to
find out what the limits are. The last thing you want is to have a
complaint filed against you for causing interference, and run the
risk of possible criminal and civil action.
Here, the US is much less limited than Europe. In the US, with
clear line-of-sight and good high-gain antennas on both ends, you can
legally get distances of 50-75km or more. In Europe, it can be
difficult to get more than 10-20km. Carefully choosing your wireless
cards (on both ends) so as to have maximum sensitivity can help a
So if you have a manufactured system
with 20dBm eirp (effective isotropic radiated power) and replace
the 7dB antenna with a 20dB one you'll strictly need to reduce the
power output of the transmitter by 13dB - by a software setting or
by adding more feeder loss.
Keep in mind that many manufactured systems are shipped with an
EIRP that is significantly *below* the maximum allowed for that area.
At issue here is not what is shipped, but what the total maximums are
in your area and how different aspects of the overall system may need
to be modified to stay under them.
Sorry that this was a bit off topic.
I don't think it was off-topic at all. I think it was a very
good message, which delivered a lot of useful information.
Brad Knowles, <brad.knowles@xxxxxxxxx>
"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety."
-Benjamin Franklin, Historical Review of Pennsylvania.
SAGE member since 1995. See <http://www.sage.org/> for more info.
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