In article ,
Geoffrey S. Mendelson wrote:
Dave Platt wrote:
I've spoken with a guy who has set up a number of reliable
point-to-point links in the Sacramento valley, using standard
unamplified off-the-shelf SOHO-type access points and/or PCI cards or
USB dongles. He said he achieves reliable performance, with a good
margin of signal strength to handle rain fade, etc., with no
amplifiers, over distances of as much as 5 miles.
It's important to point out that using these extreme high gain antennas
with out a license is illegal in the U.S. The guy that invented the
"pringles can" antenna was an FBI agent so he was not prosecuted, but
if he had been an average citizen the FCC would have come after him.
Not strictly true, although your point is well taken.
It's true that WiFi equipment must be tested and certificated as a
system. Using an off-the-shelf gain antenna, cabled to an
off-the-shelf WiFi AP/card, will almost certainly void the
certification, and then using the device becomes technically illegal
under Part 15, and unless you have a license for another service which
allows it (e.g. Part 97 ham license) you could be cited for it.
There are commercial WiFi radios whose manufacturers have tested and
certificated them with such high-gain antenna systems, specifically
for point-to-point connections. If you buy one of their radios and
one of their antennas, you can use 'em within the Part 15 rules, and
you'll be fully legal.
It's not so much the antenna itself... it's the certification status
of the antenna/radio system, as well as the EIRP.
Then the question becomes which if any of the 14 WiFi channels is
actually in the 2.4gHz ham band.
Check the ARRL's "multi-media wireless" interest group pages for
details on this. My recollection is that there are one or two 802.11b
channels whose power spectra fall within the ham-band 2.4-gig
allocation and also fall outside of the ham 2.4-gig "weak signal"
bandplan segments.
Here in Israel it's even worse. WiFi and terrestrial 2.4gHz ham activity
is limited to 100mw EIRP. If you use a gain antenna, you must reduce
the transmitter power proportionaly.
There's a similar proviso here in the U.S., but for point-to-point
links it's not as severe as that. If I recall properly, for a
point-to-point link, once you exceed 1 watt EIRP, you have to subtract
one dB of transmitter power for each additional 3 dB of antenna gain
you throw into the equation.
--
pDave Platt AE6EO
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