Re: Homebrew wifi antenna coax adapters
- From: dplatt@xxxxxxxxxxxx (Dave Platt)
- Date: Wed, 1 Aug 2007 19:32:52 -0700
In article <98asi.13044$tj6.7353@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
robert casey <wa2ise@xxxxxxxxxxxxx> wrote:
For some strange reason, wifi connectors are not compatible with normal
SMA coax connectors. The center pin is a male in an otherwise female
connector. And visa versa.
The "strange" reason is that the FCC requires it.
Part 15 devices, such as 802.11 cards, are supposed to be tested for
compliance and certificated by their manufacturer as a system (radio
and antenna together). Replacing the manufacturer-tested antenna with
a different one (higher gain, or perhaps different impedance) changes
the system's behavior, in a way which means that the tests done by the
manufacturer for Part 15 certification are no longer valid.
The FCC's position is that making such un-tested changes automatically
voids the Part 15 certification of the device, and it's no longer
technically legal to transmit using the modified device.
In order to (try to) deter people from making such arbitrary changes,
the FCC requires that makers of Part 15 radio cards with detachable
antennas use only connectors which are either proprietary, or are "not
generally available". Most manufacturers seem to have settled on
RP-SMA or RP-TNC connector for this purpose.
I've only heard of a very small number of cases (fingers-of-one-hand)
in which the FCC has cited someone for running non-certificated WiFi
equipment... and in the only case I can remember clearly, a
non-certificated amplifier was being used to push about 5 watts out
through an omnidirectional antenna, which is rather more than the
FCC's Part 15 ERP rules for WiFi will allow.
In practice, people using simple, commercially-provided "gain"
antennas with their commercial access points are probably safe
(especially if they buy the AP and antenna from the same vendor, as a
package which has been tested as a system). If you're concerned about
the potential legal risks, though, consult with a knowledgeable lawyer
(I'm not one).
There's also a ham band that shares part of the wifi band, so we
could conceivably run high gain high power ham to ham using wifi based
equipment.
This does seem to be legal, as long as you're licensed, limit your
hopped-up transmissions to the small part of the WiFi band which
intersects the ham 13 cm band, and honor the ham-radio usage rules in
re ID'ing properly, no encryption for the purpose of concealing or
obscuring the transmission (which probably means no SSL), and no use
for purposes in which you have a significant financial interest.
--
Dave Platt <dplatt@xxxxxxxxxxxx> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
.
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