On Fri, 2006-08-04 at 08:13 -0400, Andrew Kohlsmith wrote: > 1. Fresnel zones. If you're shooting over a distance there are a number of > elliptical zones which you have to try and keep clear of signal-reflecting or > absorbing material (buildings, trees, etc.). Just because you can see the > far side doesn't mean the signal will get there with any kind of usable > strength. http://www.zytrax.com/tech/wireless/fresnel.htm for more > information.
In the past I've had better luck over large bodies of water using horizontal instead of vertical polarisation... > 2. Height. The earth is round, so if you're shooting for anything over about > 10km or so you need to get up high to compensate for the curvature of the > earth. 2.4Ghz RF doesn't bend at the same rate as the earths curvature... > 3. EIRP. In order to go long distances reliably you need power. The FCC and > CRTC are pretty close in terms of what they'll allow you to send through the > air. Thankfully they let you use big-ass antennas if they're highly > directional. Unfortunately highly directional means narrow beam widths which > makes aiming less fun. Actually the Yanks are crazy, although they try to compensate by asking for "approved overall setup" meaning you have to certify the setup (but you can self certify so kind self defeating), they also required uncommon connectors which keeps most from doing anything likely to cause any harm, although out of that came a whole industry to build the new kinds of connectors, also self defeating. >From memory in the US for each dBm less in output over 20dBm (30dBm max) you get 3dBm extra in antenna gain output, or something to that effect. 10 dBm less in output and 30dBm more in antenna gain, works out at some where over 400W output from the antenna iirc. Luckily for all of us signal strength decreases at a exponential rate. -- Best regards, Duane http://www.cacert.org - Free Security Certificates http://www.nodedb.com - Think globally, network locally http://www.sydneywireless.com - Telecommunications Freedom http://e164.org - Because e164.arpa is a tax on VoIP "In the long run the pessimist may be proved right, but the optimist has a better time on the trip."
