On Wed, 16 Dec 2009 01:37:00 -0000, wrote:

Jeff Liebermann wrote:
On Tue, 15 Dec 2009 16:14:04 +0000 (UTC), "Geoffrey S. Mendelson"
wrote:

wrote:
It is not illegal if it is done on an amateur frequency by a licensed amateur.

You forgot the words "in the US".
Is using WiFi equipment for ham radio legal?
Geoff.

I don't want to comment on the legal part of the puzzle (because I
already have a headache). However, it should be obvious that there's
a potential conflict between unlicensed Part 15 operation, and
licensed part 97 operation on 2.4GHz. Place your bets and blast a way
with kilowatts on 2.4Ghz. Will 800,000 licensed US hams prevail over
perhaps 300 million unlicensed wireless devices? Want to bet on who
will win before an FCC tribunal? If there is a conflict, I'll place
my bets on Part 15.

Since 2.4 GHz is basically line of sight, few hams work 2.4 GHz, and the
Part 15 devices running under Part 15 can hop to other frequencies
including frequencies outside the ham bands, I don't see a lot of
potential for conflicts.

There's considerable overlap in frequencies in both the 2.4 and 5.7GHz
bands between Part 15 (license free) and Part 97 (ham radio). See:
http://en.wikipedia.org/wiki/High-speed_multimedia_radio#Frequencies_and_channels

Most 802.11 direct sequence modulation on the 2.4Ghz band is about
20Mhz wide leaving exactly 3 non-overlapping channels (1, 6, and 11)
to be used without mutual inference. Some access points have
"automagic frequency selection" which allegedly finds an empty channel
to use. The client radios will follow the access point channel. My
experience with this feature has been dismal and I just turn it off.

The real problem is that direct sequence 802.11 and 802.11b are not
particularly immune to interference. Sure, there's about 10dB of
processing gain, which helps. However, even a dead carrier anywhere
in the 20MHz occupied bandwidth will stop thruput dead. OFDM
(802.11g) does much better by breaking the data into 52 separate
sub-carriers. Clobber a few sub-carriers and all it does is slow
down. However, spray broadband garbage across all 52 carriers (i.e.
microwave oven or frequency hopping spread spectrum, and it too will
stop dead.

So, what are hams doing? Well there's the traditional moon bounce,
DX, and rover modes, all of which are narrow band. They mostly stay
in the bottom part of the band, which does not overlap (much) with
802.11 data. They're not a problem. There are also a very small
number of FM and ATV repeaters on 2.4GHz. Those might become a
problem, if they weren't so rare.

So, where's the problem? Several places, all of which I've seen. One
is from Part 15 wireless network owners purchasing ATV amplifier
hardware and generating what I call an alligator. That's an animal
with a big mouth, but small ears. It can be heard everywhere, but can
only hear a short distance. Kinda like what one gets when attaching a
high power amplifier to a consumer grade wireless router.

Another horror surrounds cordless phones. I caught one bozo with a
modified Panasonic 2.4Ghz spread spectrum cordless phone, with a 10
watt amplifier attached, and using it like a cell phone in downtown
Santa Cruz. I was sniffing the area trying to figure out why wi-fi
was almost useless in parts of the downtown area. This guy wasn't a
ham, but he had some relative that was build him the power amp.

The alligator owners are epidemic and are sometimes hams that have
decided that the Part 97 allows them to use high power regardless of
how much interference it creates. Hams are also a licensed service,
which takes priority over an unlicensed service. However, as I
previously indicated, if the issue ever comes before the FCC, my bets
are on 250 million wi-fi devices, versus 800,000 hams. Chances are
really good that if hams create interference by using high power,
we'll lose the whole band.

The number of conflicts are certainly minimal, as there aren't enough
hams using 2.4Ghz to make a difference. However, one high power ham
ATV xmitter, in the middle of a crowded wi-fi infested area, will
effectively jam everyone within a substantial radius. It only take
one ham operator.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558