On Wednesday 02 April 2003 10:45 pm, Richard Fennell wrote: > When u say illegal, how illegal is it? I can't seem to get a straight answer > on what to do about this and if anyone will get interruption due to my > link? Has anyone got contact details for the people I should contact with > regard to this?
Contact the Radio Authority (if you really want to) and see radio.gov.uk and radioauthority.org.uk. > My Antenna is 15db The AP is about 15db I think (same at both ends) all I > want is a connection over the 2 miles at 11mps minimum and hopefully 18 > mbps Assuming you are using an Airstation 54Mbps, according to Buffalo's datasheet it outputs 32mW (15dBm). In the UK you are limited to 20dBm EIRP so the max TX antennae gain you can use is 5dBi. (not incl. cable & connector losses.) > I don't want to upset anyone and I also don't want to break any laws > either. I just want to use this technology to provide a stable link Unless someone complains it's unlikely that the RA will bother you, and if they do, it's likely they will want to help you get legal not prosecute you. That said, you are putting out a fair amount of energy into a crowded urban area and *may* cause problems for others in your signal path. It really depends whether you cause problems and to whom. E.g. Surrey Fire Brigade use WLAN's and I guess anyone interfering with them would be more of a concern than say Joe Bloggs household user. > P.S. if I am "over powered" how easy is it to drop the output gain > without damaging the input sensitivity? One approach is to use antennae diversity to separate your TX and RX paths, thus you can have high gain RX and legal EIRP. I don't think the Airstation supports true diversity, though the datasheet is not clear. Alternately there are antennae that have differing TX and RX gain (using circulators etc.) but these cost LOTS of wonga. Assuming the Buffalo has RX sensitivity of -83dBm @ 11 Mbps (they don't say) and you use 5dBi TX and 15dBi RX then: radio output = +15dBm radio sensitivity = -83dBm at 11Mbps transmit antenna gain = +5dBi receive antenna gain = +15dBi output to air = +15dBm + 5dB = +20dBm(i) (legal) off-air sensitivity = -83dBm - 15dB = -98dBm difference = +20dBm - -98dBm = 118dB allowing 13dB signal to noise leaves 105dB difference that can be lost in the path between the transmitter and receiver. Equating this to the calculated Free Space Loss (FSL = 20log(Freq in MHz) + 20log(Dist in miles) + 36.6) Theoretical range = 1.2 Miles (2.0Km) at 11Mbps All the usual notes about RLOS, Fresnel zone infringement etc, apply. These figures are adapted from some posted to the Consume list by Malcom Cartledge. Any errors are mine. -P -- general wireless list, a bawug thing <http://www.bawug.org/> [un]subscribe: http://lists.bawug.org/mailman/listinfo/wireless
