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?
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.