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Initial WLAN antenna test

Antenna's for the 2.4ghz wireless lan band were built and then tested on a cold day in december 2001.

Written by: G4RFR ( FRARS ) Wednesday, 6 February 2002

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The main idea of this was to prove in concept that a high speed data link could be obtained over a reasonable distance.

The 2.4Ghz antennas are made from sky mini dishes, which are around 12" X 18", and have a gain of around 16-19db. The antenna's were initially made and tested with an swr meter to make sure a good 50 ohm match existed, and once this has been established, a 2.4Ghz video link was tried with some success.

The main aim of constructing these antenna's is to provide a community wireless network using the 802.11b standard, which operates in the license free ISM band of 2.4ghz. Of course, laws exist of course to prevent abuse of the band with high gain antenna's, but of course in our case, we need antenna gain to overcome coax losses, and to provide a directional element to our signal.

It would seem that being licensed radio hams, we can use these cards in the portion of 13cm's with our high gain antenna's providing the traffic is in the clear.

At the feed point of the dishes used in the link test, are a tin can feed on one dish, and the other has a double quad antenna. Both antenna's have been designed and adjusted for optimum performance on the 2.4Ghz band.

The tests performed were as follows:

1st - Simple test with about 10m seperating the antenna's. The TX used had a power output of around 10mW, and the RX was a simple diode detector. This allowed the antenna's to be adjusted, and the optimum feed point to be established.

2nd - A test over 1.1Km with wireless lan cards produced a good result, with a S/N ratio of about 26db being obtained. The path in this case was obstructed by some trees and hedges. This was a very encouraging test.

3rd - More distance was needed, so this time, the link was extended to 2.9Km but with 100% line of site. Again, a good S/N ratio was obtained, being in the order of 25db.

4th - Still more distance, so this time the link was tested over a 6Km path, with a S/N ratio of 22db being obtained. The connection speed was 11mbps and full duplex comms were tested using netmeeting and netcat. A 16K ping packet was sent at all times to verify the link.

All these tests were carried out near the Purbeck hills, as there is plenty of open space there.

Carl G6NLC was at one end of the link, and I would like to extend my thanks to him for his assistance.

Designs of the antenna's will appear on this site in the near future.

The accompianing photo shows the dish pointing to Carl who is sat in the freezing cold up at White Ways carpark. The inset picture is me, with dish and laptop setting up the 2.9Km link.

The plan is to try a 20Km test with the same dishes. The compaq wl100 card has been modified to remove the diversity antenna switch, and therefore all transmission and reception occurs via the SMA connector.

The output of the wl100 is around the 35mW mark. The compaq site quotes these cards, along with the WL200 PCI varient as having an output of 100mW. The PA in these cards, in both cases is the Intersil HFA3983 chip.

This link distance has now been beaten with our latest 14Km 802.11b link test.


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