Post by thread:[EE]: Long range with 802.11b

Here's a NZ application of internet connection over 802.11b with a 13 km range and they use multiple links to extend it even further. The only addition are high gain aerials - they are using standard devices with a normal expected range of 50 metres. May be interesting to see what range could be achieved in rocketry applications with an obvious trade-off between range and operating angle as the aerial gain goes up. http://www.idg.net.nz/webhome.nsf/NL/6427FF9C08B25D78CC256BAA00794CF2 <www.idg.net.nz/webhome.nsf/81476e1c0cf66ad0cc256896007c00e7/456b51a3 2a6977a7cc256b87007fd8c0!OpenDocument> Our local regulators advise that this is legal in this country as long as the EIRP does not exceed 4 watts. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

> >Our local regulators advise that this is legal in this country as long as > >the EIRP does not exceed 4 watts. > > YOW! Note that this is EIRP - the concentrated effective power. A dipole (or is it a completely isotropic radiator) would require 4 watts input to produce this signal level. A high enough gain antenna can do this from mWatts. Lets see simplistically what is required. A 10 mW signal is 10/4000 = 1/400th of 4 watts. Area of a sphere = 4 x Pi R^2 An antenna transmitting a circular expanding beam from inside this sphere would transmit over an area at distance R of 2 x Pi x R x h. This area is 1/400 of total area so 800 Pi R H = 4 Pi R^2 or 200 H = R. H = 1/200 R = 0.005R If I have it right this means the transmission half angle is cos^-1(0.995) = 6.4 degrees Full angle = 12.8 degrees SO The beam angle to convert 10 mW to 4 watts EIRP is about 13 degrees The power gain over a spherically unidirectional antenna is 10 x log(400) = 26 dB. A look at the ARRL antenna handbook suggests this would need about a 3 foot dish at 2.4 GHz - maybe slightly less. (Hey - I've got a 2 foot dish in my back yard - found in local inorganic rubbish collection :-) !) -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

On Sat, 4 May 2002, Russell McMahon wrote: {Quote hidden}>> >Our local regulators advise that this is legal in this country as long as >> >the EIRP does not exceed 4 watts. >> >> YOW! > > >Note that this is EIRP - the concentrated effective power. A dipole (or is >it a completely isotropic radiator) would require 4 watts input to produce >this signal level. A high enough gain antenna can do this from mWatts. Lets >see simplistically what is required. A 10 mW signal is 10/4000 = 1/400th of >4 watts. Area of a sphere = 4 x Pi R^2 >An antenna transmitting a circular expanding beam from inside this sphere >would transmit over an area at distance R of >2 x Pi x R x h. This area is 1/400 of total area so > > 800 Pi R H = 4 Pi R^2 > >or 200 H = R. H = 1/200 R = 0.005R > >If I have it right this means the transmission half angle is cos^-1(0.995) = >6.4 degrees >Full angle = 12.8 degrees > >SO > >The beam angle to convert 10 mW to 4 watts EIRP is about 13 degrees >The power gain over a spherically unidirectional antenna is 10 x log(400) = >26 dB. > >A look at the ARRL antenna handbook suggests this would need about a 3 foot >dish at 2.4 GHz - maybe slightly less. >(Hey - I've got a 2 foot dish in my back yard - found in local inorganic >rubbish collection :-) !) Yes but the other way to interpret it is that you can run 4W/sqrt(2) into a dipole and cover 13 miles in ALL directions. As in broadcast. Re-YOW! That NZ must be the last free place on earth for hams and such ;-). They probably got away with it because they are a school. In other countries it's illegal to use an antenna with gain for certain services (see 433MHz etc). Peter -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> >> >Our local regulators advise that this is legal in this country as long as > >> >the EIRP does not exceed 4 watts. > >Note that this is EIRP - the concentrated effective power. A dipole (or is > >it a completely isotropic radiator) would require 4 watts input to produce > >this signal level. > Yes but the other way to interpret it is that you can run 4W/sqrt(2) into > a dipole and cover 13 miles in ALL directions. As in broadcast. Re-YOW! > That NZ must be the last free place on earth for hams and such ;-). They > probably got away with it because they are a school. > > In other countries it's illegal to use an antenna with gain for certain > services (see 433MHz etc). Now that's a very good point. I think the capabilities may have outrun the arms length regulators awareness. I haven't looked at the terms of the 2.4 GHz ISM service but I suspect that there will also be an absolute power limit on the transmitters - as I agree there should be for a free to use ISM band that everyone uses. I don't think being a school has anything to do with it. People are selling commercial point to point internet links in this band. It hadn't occurred to me until now that they are probably using absolutely standard 802.11 cards to do this. A web search turned up many many people doing this overseas. I'm afraid I'm going to have to add it to my list of things to try (someday). Russell McMahon -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

I'm currently using 802.11b on my local network and 1 watt amps with 24db dishes to get from 5 different homes, to my place of business, remote mountain top sites where I have radio equipment that needs monitoring and control, and to the Internet. The longest span on a single hop is 24 miles. From one end of my network to the other is 112 miles! Easily throughputs 11mbps (roughly 10baseT) even in a pouring rain! I have weather stations at each site sending data to http://www.wunderground.com, and cameras shooting and sending pictures every 30 seconds through the network from each site and I can still download a 24 meg file from the web through it in less than 1-1/2 minutes even on a bad day. The cameras are nice. I can sit at work and keep a browser window open looking at my four cameras sequencing around the outside of my house. We can watch the dog in the back yard, note when the postman delivers the mail and when the UPS man arrives. My partner had a camera set up looking at the street from his house and we even caught juveniles stealing American flags from the front of peoples houses. (The police were intrigued with our little setup. The sheriff wanted to know if he could have the same thing at his house too). A linux box logs all pictures every 6 seconds and stores them for 3 months on a 60gig HD. I can do the same from home by watching my place of business too. Our local ISP's use the same 802.11b network to provide wireless internet access to customers (including the local university), all over our town. They use ROR's and COR's and AP's blanketing the city to achieve this. Of course we had all our radio cards flash upgraded recently to prevent "Air Snort" from causing security breeches. We use 128 bit encryption exclusively. The only thing we have to watch out for are nasty microwave ovens and Bluetooth. Rick "Peter L. Peres" wrote: {Quote hidden}> On Wed, 1 May 2002, Russell McMahon wrote: > > >Our local regulators advise that this is legal in this country as long as > >the EIRP does not exceed 4 watts. > > YOW! > > Peter > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics