Tim, These calculations incorrect, if to consider as their by exact, then the communication using reflection is impossible, for example from buildings or from the Moon :)
Path loss for 2.4GHz -> -115 -20log(d_km) ;) -Ivan > On Wed, May 29, 2002 at 05:00:30PM -0600, Mike Avery wrote: > > On 29 May 2002 at 11:02, Tim Pozar wrote: > > > > > On Wed, May 29, 2002 at 10:44:59AM -0700, Tim Pozar wrote: > > > > As an example... > > > > > > If we had a 24 dBi antenna on both ends of a point-to-point link > > > > with the legal max power of .25 Watts (FCC 15.247) we would have a > > > > fade margin of 47.775 dB (with a 80 dBm RX threshold) over a 1 mile > > > > link. If we had a passive repeater connecting two 1 mile links we > > > > would have to multiply the pass loss of one link (104.2 dB) by 2 and > > > > the antenna gain (48 dBi) by 2. This would have a total path loss > > > > of 108.4 dB and would put the RX signal at -88.42 dBm. > > > > > Whoops... That should be 208.4 dB. > > > > I believe you were closer the first time at 108.4 dB. dB > > are not a linear scale, and a doubling or halving of signal is > > a 3 db change. So, if you lose 104.2db on each leg, the > > total loss would be 107.2 db because you have doubled the > > loss - or added another 3 db of loss. > > Hmmm... I may not have described how this works very well. Sorry > gang... > > Say if I have a link that goes through a passive repeater, each > link has path loss. Path loss it pretty easy to calculate (check > out http://www.lns.com/papers/pathcalc) and for a 1 mile 2.4 GHz > path it is just slightly more than 104.2 dB. Since you have two > links, you just add these number together with other loss factors > such as coax or connector loss. On the "gain" side of things you > have the transmitter power and antenna gain. You would add these > number together. > > An sample calculation (from pathcalc.pl - see above)... > > Frequency = 2.4 GHz > TPO = .25 Watts > TPO = 23.9794000867204 dBm > TX line loss = 3 dB > TX ant gain = 24 dBi > Path length = 1 miles > Path loss = 104.204224834232 dB > RX ant gain = 24 dBi > RX line loss = 3 dB > RX signal = -38.2248247475117 dBm > RX threshold = -80 > Fade margin = 41.7751752524883 dB > > Since we have two links, we need to double the line loss, antenna > gain and path loss numbers as we have two links and 4 antennas. So... > > TPO = 24 dBm > TX line loss = - 3 dB > TX ant gain = + 24 dBi > Path loss = - 104.204224834232 dB > Repeater RX line loss = - 3 dB > Repeater RX ant gain = + 24 dBi > Repeater TX ant gain = + 24 dBi > Repeater TX line loss = - 3 dB > Path loss = - 104.204224834232 dB > RX ant gain = + 24 dBi > TX line loss = - 3 dB > ======== > - 100.4 dBm > > Since most radios want about - 80 dBm for a signal, this path won't > work as it is 20 dB below the RX threshold. (This time I calculated > transmission and connector line loss.) > > Tim > -- > general wireless list, a bawug thing <http://www.bawug.org/> > [un]subscribe: http://lists.bawug.org/mailman/listinfo/wireless -- general wireless list, a bawug thing <http://www.bawug.org/> [un]subscribe: http://lists.bawug.org/mailman/listinfo/wireless
