|
||||||||||
Yeah.. I actually got several indoor B's back in 2003 and have them at my shop and have deployed several outdoor B's in NYC (through Tanis) ---and had to keep them all on one channel per switch, btw :). Anyway, what causes the interference if you're using non-overlapping channels on a WRAP with 2 wireless cards with m0n0?... and how is it noticed? Lower data rate? doug On Nov 13, 2005, at 9:40 PM, Jim Thompson wrote: > Douglas Stringer wrote: > >> I agree, however it doesn't stop lots of vendors from doing it >> (besides Vivato) i.e. Tropos! > > Um, what Tropos is trying and what Vivato did are two *very* > different things. Vivato can actually make multiple radios work > via hardware mods that sample the baseband's CCA line (or its > equivalent). Tropos ... can't, and as such, their performance > stinks. They are good at marketing, however. :-) > >> Even with 22+ MHZ separation between channels (1 and 11), there >> are issues that I've seen... though I'm not sure what they are. > > In the 2.4 GHz ISM band, the IEEE defines 14 channel centers 5 MHz > apart. In the US 11 of these can be used. > > The center frequency for ch1 is 2.412GHz, and the center frequency > for ch11 is 2.462GHz. This is 50MHz, not 22MHz. > > The spectral mask requirements for 802.11b state that the signal > must be attenuated by at least 30 dB from its peak energy at ±11 > MHz from the center frequency, and attenuated by at least 50 dB > from its peak energy at ±22 MHz from the center frequency. > > The issue is that the radios on the market don't do much better > than the minimum adjacent channel rejection required by the IEEE > standard. For 802.11b the required ACR is 35dB. You can probably > google my name and "ACR" to get the rest of the math, since its not > appropriate on the m0n0wall list. > >> Is this a case of harmonic frequencies.... or is it the radiation >> mask extending down and beyond the 22MHz channel (and across the >> band), or something else?? > > The second, essentially. > > Jim > |