[TriLUG] Wireless access

[Tanner Lovelace]

Ron Joffe wrote:
 > Would hooking up a Yaggi antenna directly to a commercial 802.11 broadband
 > bridge without amplification violate any FCC Rules?

It really depends on how much power bridge puts out.  FCC Rules
section 15.249 sets out how much power you can run.

http://frwebgate.access.gpo.gov/cgi-bin/get-cfr.cgi?TITLE=47&PART=15&SECTION=249&YEAR=2000&TYPE=TEXT

802.11[a|b] is limited to a field strength of 50 millivolts/meter
measured at 3 meters.  (See http://www.microindustrie.com/fcc/trans.htm
for how to calculate this.)  That's not a lot.

In addition, the actual act of hooking up an external antenna may
run counter to FCC rule 15.203.

http://frwebgate.access.gpo.gov/cgi-bin/get-cfr.cgi?TITLE=47&PART=15&SECTION=203&YEAR=2000&TYPE=TEXT

I'll quote here:

   An intentional radiator shall be designed to ensure that no antenna
   other than that furnished by the responsible party shall be used with
   the device. The use of a permanently attached antenna or of an antenna
   that uses a unique coupling to the intentional radiator shall be
   considered sufficient to comply with the provisions of this section. The
   manufacturer may design the unit so that a broken antenna can be
   replaced by the user, but the use of a standard antenna jack or
   electrical connector is prohibited.

Note that there are some exceptions, but there is not a blanket
exception for the wireless network frequencies.  There is an exception
for an "intentional radiator" that must be "professionally installed",
which might cover something like this, but it goes on to say:

   However, the installer shall be responsible for ensuring that the
   proper antenna is employed so that the limits in this part are not
   exceeded.

So, you really need to sit down and look at a) how much power the bridge
puts out and b) how much gain the antenna gives you and then calculate
the measurements.

Note, btw, that I've heard that point-to-point links are allowed
higher field strength measurements, but I can't seem to find where
that is mentioned in Part 15 of the FCC rules.  If anyone else
can find that, I'd be interested in seeing it.  Part 15 of the FCC
rules can be found here:

http://www.access.gpo.gov/nara/cfr/waisidx_00/47cfr15_00.html

Cheers,
Tanner
-- 
Tanner Lovelace | lovelace(at)wayfarer.org | http://wtl.wayfarer.org/
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