900ghz? I bet it would be great nlos, you could just burn through the trees :) On Aug 22, 2013 1:35 PM, "Fred Goldstein" <[email protected]> wrote:
> On 8/22/2013 4:09 PM, Steve Barnes wrote: > > But Mike that is the Rub. All things are never the same. 900 is dirty > and Susceptible to so much noise and reflection because the signal does not > die as quick. I understand the “Theory” but still have a hard time > understanding how a slower carrier wave (900MHz) can carry the same Data as > 5800MHz carrier wave but I know that it could in a vacuum. The issue is we > don’t live in a vacuum. **** > ** ** > > > The "carrier" frequency has no impact on data-carrying capacity. > Shannon's Law dictates that the capacity of a channel to carry information > is a function of its bandwidth and its signal to noise ratio. If it is 10 > MHz wide from 902 to 912, or 10 MHz from 5800 to 5810, it's still 10 MHz. > And if the SNR is the same, the usable capacity is the same. > > The issue of vacuum relates to things that make a path worse than the > theoretical free space attenuation would dictate. Take the 60 GHz band > (57-64 GHz). It has a primary allocation for satellite-to-satellite use. > Now there's your vacuum! It's unlicensed because oxygen absorption at 60 > GHz is around 14 dB/km, so anything done down here at the surface is > unlikely to reach a satellite. It's thus great for high-speed WLAN use, > like WiGig. And the FCC last week raised the power limit for outdoor > point-to-point use to 82 dBm, provided the antenna gain is 51 dB (derated 2 > dB for each dB of lower gain that the antenna has). This will allow huge > bit rates because it's 7 GHz wide, but range at normal atmospheric pressure > is going to be very limited. > > 900 GHz is nice in wooded areas because it gets through foliage much > better than higher frequencies, but in many places it's already congested > with meter readers and other devices. Those, plus the limited bandwidth, > are more likely to limit real-world performance than anything else. A 6 > GHz TVWS channel will do as well as 6 GHz on higher frequencies, though. > Better, actually, if you can get a big enough antenna. But lower > frequencies tend to need bigger antennas. Maybe those old TV antennas we > used to all have before cable will make a comeback. ;-) > > -- > Fred R. Goldstein fred "at" interisle.net > Interisle Consulting Group > +1 617 795 2701 > > > _______________________________________________ > Wireless mailing list > [email protected] > http://lists.wispa.org/mailman/listinfo/wireless > >
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