So what is it you would say determines wither or not my signal will be
received on the other end? I mean with just a regular soho wifi access
point in open space you can only communicate within a couple hundred
feet (That's open space). If gain/wattage isn't so important when we're
talking distance.. what is? Line of site? Are you saying that that I
can shoot my 30mw signal from my soho access point couple of miles?

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.

The key to doing this are a clear line of sight, an antenna with high
directional gain at each end of the link, and careful aiming. Getting
the radio right up at the antenna (rather than at the end of a length
of coax) is also beneficial.

The carefully-aimed highly-directional antennas give you several
advantages, over a standard SOHO omni antennas. The directionality
increases the effective radiated power of the transmitter (50
milliwatts through a 20 dBi antenna is equivalent to 5 watts
isotropic), it increases the receiver's effective sensitivity by the
same degree, and it makes the receiver _less_ sensitive to
interference arriving from other angles (e.g. competing transmitters).

Also, with proper choice of antenna, you can select the signal's
polarization angle. Since most home and business access points seem
to use vertically-oriented antennas (and thus a vertically polarized
signal) you can reduce interference problems by using point-to-
point antennas which are horizontally polarized.

The guy I spoke with was not complementary about the idea of trying to
"blast" signals through by using high-power transmitters or
amplifiers, and blanketing a large area with the signal.

You can buy wire-dish parabolic antennas for the 2.4-gig ISM radio
band quite easily. I think I've seen 'em advertised as having 15 to
19 dBi of gain. One of these at each end of the link would be a good
place to start.

--
Dave Platt AE6EO
Hosting the 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!

Ok, I 'think' I understand now :/

Tekmanx wrote:
Also, I heard 802.11g sucks outdoors. This true? And would you guys say
my 400mw radio is overkill for 4-10mile shot?


You seem to be getting too much information and not answers to your
questions.

400 milliwatts is plenty of power. The performance of your system will
be governed by two simple factors: how high are the antennas; and, how
sensitive is the receiver?

For ten miles your antenna height above average ground should be close
to 100 feet. For seventeen miles you need an antenna height of close to
300 feet. I suspect both heights are excessive for your application.
Also, the cables connecting your transmitter to the antenna have losses.
So, mounting the transmitter at the top of the antenna would be
preferred. An alternative to the 100 foot antenna would be 70 feet
antennas, one at the transmitter and one at the receiver.

Receiver sensitivity is unknown. I regularly communicate 20+ miles with
500 milliwatts from a ham radio walkie talkie. [the receiver is located
on top of a mountain] Most communiation grade radios can receive a
signal as small as 0.000000000000002 watts. [one millionth of a volt].
So, you can see why I say 400 milliwatts is plenty. So, the receiver you
use should have a moderately good sensitivity 5 microvolts or smaller.

Over relatively flat terrain, with very modest antenna [20 feet high] a
four mile circuit should be possible. Longer paths will require spending
$$$.

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.

Then the question becomes which if any of the 14 WiFi channels is
actually in the 2.4gHz ham band.

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.

Geoff.
--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
IL Voice: (07)-7424-1667 IL Fax: 972-2-648-1443 U.S. Voice: 1-215-821-1838
The trouble with being a futurist is that when people get around to believing
you, it's too late. We lost. Google 2,000,000:Hams 0.

Thank you so much Amos! I was aiming for a 40feet-ish tower. Tripod
base with an adjustable inner tubing which is where the antenna will be
placed on at the top. So basically I was thinking 20ft tall tripod with
cup-like guides allowing me to adjust the inner 30foot long inner
tubing/pole up to 20feet on top of the tripod giving a total high of
40ft(10feet of the inner pole will sit inside the tripod). I'm
currently in the process of drawing up a diagram to show a local metal
welder, but that's my basic idea right now.

Here's my first draft. - http://tekmanx.serveftp.com/~tekmanx/pole.gif

"Tekmanx" wrote in message
ups.com...
Here's my first draft. - http://tekmanx.serveftp.com/~tekmanx/pole.gif


Hi Tek

Your ambition impresses me. 40 feet seems awful high unless those
support legs are anchored well.
I have a little WiFi site that uses surplus satellite TV dishes with
BiQuad illuminators. I have chosen to locate the Access Point at the
transmitting antenna in an effort to minimize the loss to the coax to the
computer. I have a Bridge at the receiving computer end. CAT-5 cable
takes the signals to the computers.

Jerry

Hi Amos

From memory the Cisco 5.6GHz box had a path prediction sensitivy number
of about -87dBm. ie full speed with that input to the RX. I suspect that
at a lower data rates and extra 10dB might be a good number to use. I
have seen that larger microwave system manufacturers do publish their
specs so look it up for the equipment that is going to be used.

FM rcvs on 2M can often go to about -117dBm. An SSB rcvr on 2m with a
preamp hits thermal noise at about -141dBm. This also needs a good human
ear.

Cheers Bob VK2YQA

Amos Keag wrote:
Receiver sensitivity is unknown. I regularly communicate 20+ miles with
500 milliwatts from a ham radio walkie talkie. [the receiver is located
on top of a mountain] Most communiation grade radios can receive a
signal as small as 0.000000000000002 watts. [one millionth of a volt].
So, you can see why I say 400 milliwatts is plenty. So, the receiver you
use should have a moderately good sensitivity 5 microvolts or smaller.

Well I plan to have a 5-6' squared concrete slab inwhich the tripod
legs will be bolted down to. The access point will sit in a outdoor
enclosure prolly 2-3feet away from the antenna on the pole. The inner
tubing will come down for easy access making the total height of the
tower 30ft. There's just soo much variables involved that determine if
this thing works properly.. so I'm planning to overshoot in hopes that
I will get it just right.

Here's the access point :
http://www.wisp-router.com/product_i...02459103e1168b

And the radio:
http://www.wisp-router.com/product_i...roducts_id=399

Plan to use a based OS on this setup.

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
Hosting the 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!