Slashdot Mirror
UK Approves of 5.8GHz For Rural Broadband
Tandoori Haggis writes "BBC News reports a major decision by UK Government to approve the use of 5.8 GHz C-band for use with wireless broadband. A prime consideration is the desire to provide broadband access for rural areas
where broadband cable might be prohibitively expensive to impliment. Previously there had been resistance to freeing up 5.8GHz because it is in an area of the RF spectrum used by C-band radars."
...on the issues involved in deregulating this part of the spectrum can be found here.
The Army reading list
Satellite broadband for 19.99 per month
There are places where the networks are not touching,and there are places where they are-Boeing's Lori Gunter
It depends on the signal encoding and protocols transmitted on that band. In this case, 5.8GHz is an additional signal band being added to the group of signal bands utilized by the IEEE 802.11a and 802.11g standards. The encoding used by those standards (Orthogonal Frequency Divison Multiplexing, link) allows for a maximum clean-room EM-free speed of 54Mbps. In reality, once you factor in interference, equipment quality and distance, you can only really reach approxmiately 20Mbps, which will still outstrip most consumer-level broadband options.
IANASS.
SCREW THE ADS! http://adblock.mozdev.org/ Proud user of teh Fox of Fire - Registered Linux User #289618
Once again an AC post gets no respect while an idiotic post is modded up soley becuase it was not posted anonymously.
The AC is correct here, comparing VHF signal propagation to that of Microwaves is comparing appples and oranges. They are two very different beasts. An FM brodcast signal broadcast at 98MHz has a signal wavelength of ~3 meters. This means the signal does indeed seem to "bounce" around fixed obstacles such as buildings and terrain. On the otherhand, a 5Ghz microwave signal has a wavlength of ~6 cm. In otherwords you have an approximate 3 cm margin of error when aiming a waveguide or parabola at these frequencies.
The microwave frequencies have some other characteristics that make them difficult to work with. Unlike in the VHF/UHF world, here the term "line of sight" means exactly that - there must not be *any* obstacles in the signal path between transmitter and receiver. And yes this includes trees and/or other folliage as vegetation significantly attenuates RF energy at these frequencies. Becuase of the wavelengths involved here, nearly anything containing water (including animals) will absorb the signal and convert the RF energy to heat energy.
If you have ever installed an 18" satellite dish, you can appreciate how difficult and tricky microwaves are to work with. Keep in mind however, this is not a fair analogy as you are aiming at a fixed transponder in the sky about 25,000 miles away (which contributes somewhat to signal spread, thereby giving you abit more room for error) putting out 120 watts (not counting the attenna gain). Compare this to the 250mw max under FCC rules for both 802.11b and 802.11a operation.
In short, what i'm trying to say here is working with 5Ghz equipment is tricky and you'll likely not fair too well if you approach installing an antenna in the same haphazard methods you can take when putting up radio or tv aerial.
You're ignoring diffraction, which of course is more obvious at larger wavelengths. FM radio seems more line-of-sight than AM because the smaller wavelength bends around properly-sized objects (read people-sized houses and small hills) less well.
An FM radio signal (about 100 MHz) has a wavelength of roughly 3 meters. Some brick houses aren't that much larger than this, so you'll can get some diffraction around the house.
A 5.8 GHz signal has a wavelength of about 1/60 this, or roughly 5 cm. So yes, expect much smaller objects to significantly obscure your receival of the transmission.
Finally, what really matters is the index of refraction of whatever material is 'obscuring' the signal. I'm not really sure, but I would guess that wood and brick would be more opaque at 5.8 GHz C band than at 100 MHz.
make world, not war