[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 great deal.

                               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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