The popular low loss wifi coax is the LMR series. LMR100 is about 1/8"
thick and should only be used for short pigtails. LMR200 is about 1/4"
thick and looks a lot like RG-59 and is good up to 10 or 15'. LMR400 is
1/2" thick and looks like RG 213 but lower loss.

To give you an idea of the relative losses, that 30' run in LMR100 would
loose 11.7db or about 93% of the signal. In LMR200 it would loose 5 db or
about 58% and in LMR-400 it would loose 2db or about 37%.

There is an online calculator at:
http://www.timesmicrowave.com/cgi-bin/calculate.pl

One advantage of the EUB-362 is that you can run the USB cable up to 15'
(with a powered hub up to 30')with no loss and use a shorter coax to the
antenna.

Extra antenna height doesn't get you much because the absolute range over
water of a 200mw wifi signal on a 9db omni antenna is about 2 miles. With
the antenna at 10' the horizon is twice that far. Anything much higher than
the Bimini frame makes no real improvement. In some cases it could actually
work against you. Many marinas use sectorized antennas with narrow vertical
patterns and aim them down towards the end of the outer docks to get maximum
signal within the marina and minimize the spread to boats outside. If you
are anchored off the marina the antenna can be to high to be in the sweet
part of the beam.

An example in reverse is at Trellis Bay, Tortola. The BVIWifi antenna is on
the roof of the Trellis Bay Cyber Cafe. The pattern is 10 degrees vertical
and 180 horizontal and is aimed out into the anchorage. On the beach 50' in
front of the antenna a laptop will not see the signal but 30' further out on
the dinghy dock it comes in strong.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Wayne.B" wrote in message
...
On Fri, 21 Jul 2006 04:13:05 +0000 (UTC), wrote:

Wayne, just want to be clear how you are doing this. Is the unit kept
inside and you run a cable outside with the antenna on the end? Or is
the whole unit mounted outside? If the former, any indications on
signal loss per cable length?

Is there a way to feed this into a router? Would like to be able to use
my Vonage phone service and also feed other computers in my boat.

Yes, the USB adapter is inside the main cabin feeding a 30 ft run of
low loss coax cable through an adapter (SMC to type N connector if I
recall correctly).

The antenna looks like this:

http://tinyurl.com/s6vkg

I don't know the loss figures on the cable but shorter is always
better at these frequencies. What I can tell you is that overall
system performance is a great deal better than anything else I've
tried previously. CompUSA also sells a Hawking remote
amplifier/preamp which could be installed near the antenna if mounted
in a watertight enclosure.

I don't know of any way to feed a router unless you can figure out how
to get ICS (Internet Connection Sharing) to work using a USB primary
network connection. If that is important to you, I'd recommend
looking at a remote external WiFi adapter with an ethernet interface.

The folks that I bought my USB adapter from also have a wide variety
of other components that you might find applicable:

http://www.wlanparts.com/

On Fri, 21 Jul 2006 10:48:42 -0400, "Glenn Ashmore"
wrote:

The popular low loss wifi coax is the LMR series. LMR100 is about 1/8"
thick and should only be used for short pigtails. LMR200 is about 1/4"
thick and looks a lot like RG-59 and is good up to 10 or 15'. LMR400 is
1/2" thick and looks like RG 213 but lower loss.

To give you an idea of the relative losses, that 30' run in LMR100 would
loose 11.7db or about 93% of the signal. In LMR200 it would loose 5 db or
about 58% and in LMR-400 it would loose 2db or about 37%.

Thanks Glenn, looks like I have the LMR400.

Are you saying that path loss at 2400 MHz precludes distances over 2
miles regardless of antenna gain or height?

"Wayne.B" wrote
..

Thanks Glenn, looks like I have the LMR400.

Are you saying that path loss at 2400 MHz precludes distances over 2
miles regardless of antenna gain or height?


You can get considerably further with a super high gain antenna but on a
sailboat there is a practical limit. Antennas achieve "gain" by restricting
the radiation to a desired pattern. With a beam you can get a lot of gain
but restricted to a narrow cone which on a boat moving around at anchor it
would be useless. Omni directional get higher gain by flattening the
doughnut. A 5db omni has about a 60 degree vertical spread. an 11db might
have less than 10 degrees of vertical spread. Once you get past about 11db
the pattern is so flat that the slightest rocking will make the signal fade.
8.5 to 9db is about optimal on a sailboat.

If both antennas are at 10' the line of site distance is about 8.5 statute
miles. Assuming the receiving antenna is not laying on the ground the
height over about 10' or 15' is not going to make a lot of difference
because at the low power of wifi the signal is not going to make it that
far.

You add and subtract DB to find the effective radiated power so a 200mw
transmitter is 23db. Subtract 2 db for loss in the LMR400 and add back 8.5
for the antenna and you are at 29.5db radiated in the desired pattern.
The receive sensitivity on the UEB-362 is about -92db which is about as good
as it gets. Add a net of 6.5 for the antenna and cable and you are
at -98.5. You also need 5 or 6 db to separate out the signal from the
noise. The total maximum field loss you can have and still maintain a link
will be 29.5 + 98.5 - 6db margin = 122db. In absolutely perfect line of
site conditions a field loss of 122db is about 7 miles but that is rarely
possible. Just 2 or 3 db difference in performance or field loss will cut
that dramatically. As a practical matter you will be lucky to get a
reliable connection most of the time at much more than half that distance.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

On Fri, 21 Jul 2006 13:05:17 -0400, "Glenn Ashmore"
wrote:

As a practical matter you will be lucky to get a
reliable connection most of the time at much more than half that distance.

Thanks, interesting analysis.

In article aP7wg.626$ok5.203@dukeread01,
"Glenn Ashmore" wrote:

"Wayne.B" wrote
.

Thanks Glenn, looks like I have the LMR400.

Are you saying that path loss at 2400 MHz precludes distances over 2
miles regardless of antenna gain or height?


You can get considerably further with a super high gain antenna but on a
sailboat there is a practical limit. Antennas achieve "gain" by restricting
the radiation to a desired pattern. With a beam you can get a lot of gain
but restricted to a narrow cone which on a boat moving around at anchor it
would be useless. Omni directional get higher gain by flattening the
doughnut. A 5db omni has about a 60 degree vertical spread. an 11db might
have less than 10 degrees of vertical spread. Once you get past about 11db
the pattern is so flat that the slightest rocking will make the signal fade.
8.5 to 9db is about optimal on a sailboat.

If both antennas are at 10' the line of site distance is about 8.5 statute
miles. Assuming the receiving antenna is not laying on the ground the
height over about 10' or 15' is not going to make a lot of difference
because at the low power of wifi the signal is not going to make it that
far.

You add and subtract DB to find the effective radiated power so a 200mw
transmitter is 23db. Subtract 2 db for loss in the LMR400 and add back 8.5
for the antenna and you are at 29.5db radiated in the desired pattern.
The receive sensitivity on the UEB-362 is about -92db which is about as good
as it gets. Add a net of 6.5 for the antenna and cable and you are
at -98.5. You also need 5 or 6 db to separate out the signal from the
noise. The total maximum field loss you can have and still maintain a link
will be 29.5 + 98.5 - 6db margin = 122db. In absolutely perfect line of
site conditions a field loss of 122db is about 7 miles but that is rarely
possible. Just 2 or 3 db difference in performance or field loss will cut
that dramatically. As a practical matter you will be lucky to get a
reliable connection most of the time at much more than half that distance.

very nice articulation of "Radio Path Engineering for Dummies 101"

Bruce in alaska
--
add a 2 before @