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Parabolic Antennas Parabolic antennas are generally grid type and have more oomph than your smaller directionals. They are also a lot bigger and are easily noticed by neighbors. You can usually pick these up for less than $100.00. If you have covenants or homeowner association rules banning antennas, using a Primestar dish may be the loophole you need to get around those rules; just don't tell them that it isn't actually for satellite TV.
There has been talk on the MailingLists of adapting surplus DBS dishes (e.g. Primestar, DirecTV) for 2.4GHz use. A few of the comments point to this surplus Primestar dish setup reporting 10-mile line-of-sight coverage at 22dB gain.
How 'bout a 26-mile hop via 2.4GHz parabolics tested by these folks at the Maui High Performance Computing Center at the University of Hawai'i . Whooooee! <--doesn't workie! <--neither for me!!
A source of these, used and surplus, is Aerialix.
Heres a guide on how to use a DirectTV antenna for 802.11 -http://people.wallawalla.edu/~Rob.Frohne/Airport/Primestar/Primestar.htmll
Trevor Marshall has a guide on how to use a BiQuad for a dish feed. http://www.trevormarshall.com/biquad.htm
There's also a guide for modifying Conifer antennas for wireless networking - see http://martybugs.net/wireless/conifermods.cgi
Here is a guide on how to make a small clyndrical parabolic reflector for your access point. It yeilds ten or twelve dBi in a trivial to construct package which can be made with a Pringles Can and sissors. Stick it in a window and you can easily complete a 1 km link between two nodes which have clean LOS, if the other end is similarly equipped.
When tested with a MA111(a usb card that does not have any way to connect an external antenna) there is about a 20% increase in signal strength. If both sides have a reflector the gain is 40%. The reflectors were built out flashing(roofing) and plywood. you can make about 10 reflectors for a little more than $5 http://www.freeantennas.com/projects/template/index.html
calculate your own template: http://www.uvigii.hit.bg/TMP/Parabola.xls or http://www.uvigii.hit.bg/TMP/Parabola.xls.zip Some math: http://mathworld.wolfram.com/Parabola.html
