Skip,
Yes, I remember your earlier search for a cruising sailboat and your
consideration of the Fantasia 35. I am happy to hear that you have selected
and purchased a vessel and indeed are well underway with your refit. It's
too bad you couldn't fit into the aft skippers bunk. I am confident that
with your enthusiasm, you would have been a regular on the Fantasia 35 forum
http://www.fantasia35.com/disc5_toc.htm
My wifi system is fully operational however it is temporally installed. The
Wifi Bridge is installed in a nema enclosure and hoisted to near the top of
the mast.
http://www.fantasia35.com/images/wifi-22.jpg A permanent
installation shall be completed the next time I pull the mast. The POE
interface box is mounted below and near the computer. (
http://www.fantasia35.com/images/wifi-05.jpg )
The key factor regarding the decision to mount the bridge near the top of
the mast relates to the fact that at the 2.4 GHz frequency of the 802.11g
wifi bridge, a significant signal loss in the transmit and receive modes
will be experienced with a transmission line in the 60 foot range. When one
compares the losses found in a standard Wifi access point with an integrated
antenna the total cable loss values may be considered zero. This is because
the antenna attached to the access point is about 1 inch from the
transceiver.
If I understand your intentions, you plan to install a high gain mast top
802.11g antenna and locate the bridge or access point down below. You
therefore will be forced to use a coax cable at least 60 feet in length and
will therefore experience significant signal losses. These cable losses
reduce the signal energy between the radio base station and the antenna. For
example a low loss antenna cable has a loss of 0.23 dB per foot at 2.4 GHz.
Standard loss cable is often closer to 1 dB per foot. For cable runs less
than roughly 10 feet the default value of 3 dB can be used assuming you are
using a top quality (and expensive) coaxial cable type.
The bottom line here is why use a coaxial cable where significant signal
losses will be present versus using a cat-5 cable to achieve the desired
antenna height. The theory supporting the significant signal loss at 2.4 GHz
over a 60-foot coaxial cable is as follows. The electrical resistance is in
a cable is the result of opposition to the movement of electrons. The power
output of a cable can be derived from Ohm's and Watt's laws when the voltage
is not alternating (DC current.) When a signal is alternating (at, for
example, 2.4 GHz) the moving electrons tend to push away from the core of
the conducting cable and move towards the outside of the cable. This is
called the skin effect. In essence, it's as though the cable had less
cross-sectional area than the area that is actually present. Skin effect
causes the current to occupy a smaller cross-sectional area. Consequently,
the relative resistance to current flow is greater for alternating current
than for direct current.
"Skip Gundlach" skipgundlach sez use my name at earthlink dot fishcatcher
(net) - with apologies for the spamtrap wrote in message
...
Hi, David, and group(s),
The solution I described will not use the wifi receiver internal to your
laptop due to the limitations I described in my earlier post. Instead
will
use your laptop's Ethernet connection, which runs into a simple POE
interface box. (See the following url for the POE wiring instructions
http://www.nycwireless.net/poe/ ).
Thanks for the link. Below, you may see why this might not be needed for
my
setup.
The input to this POE box is dc power and the Ethernet connection from
your
computer. The DC power comes from the AP or Bridge supplied power
adapter.
The output of the POE box is a cat-5 Ethernet cable spanning up to 300
feet
in length. This cable runs to your nema enclosure and now combines the DC
power and Ethernet.
If your access point or bridge is compatible with the IEEE 802.3af
standard
one simply plugs the cat-5 cable into the AP or Bridge Ethernet
connector.
If you do not have a compatible AP or Bridge one simply splits off the DC
power and wires it directly to the PCB's dc input power terminals.
This solution works equally well irrespective of the use of a desktop (
http://www.fantasia35.com/images/nav-1-03.jpg ) or laptop computer within
your vessel.
I hope this clarifies my wifi implementation strategy.
Indeed. Are you up and running with it? Do you have an antenna stick
mounted on the mast?
You may not recall, but the F35s were on our short list. I recall seeing
your setup in the website until we actually got aboard one and found that
we
were unable to adequately address the stern berth (see the forum archives
for discussion). Your boat looks to be an absolutely marvelous example of
the type.
As much as might be achieved, I'm even, now, considering doing up-the-mast
with a cat5 (or any other 12V) feed to a bridge in a waterproof (NEMA)
box,
thence to an external antenna
http://www.keenansystems.com/store/c...1401cfa1d316d4
and
http://www.keenansystems.com/store/c...1401cfa1d316d4
an 8.5 dB gain antenna atop the mast just above the box.
There's some potential for a couple of miles, and the added enhancement of
our ability to use our laptop ashore, communicating with the boat, or, of
course, both the nav and topsides (the one we'd carry ashore, if we had
to)
computers on at the same time if we cared to do so.
I'm also looking into fab-corp.com products as potentially having more
gain
in the antenna portions. They may also have some bridge solutions, but I
have not yet had a response to my query about their total solution ideas.
However, as attractive as cat5 is for getting signal up the mast, it makes
me tied to the boat as I understand your setup. For that reason, I don't
know that I'd pursue that. *IF* - maybe a big "if" - I can make this
work,
I'd be able to see that bridge from anywhere on or even pretty far away
from
the boat, with either of the two laptops (one "shoreside use" and other
"nav
use" we expect to have aboard. So, aboard could be in communication with
shoreside via IM, for example, or, better (for our circumstances), we
could
be in communication with anyone in the world via VOiP. My current
carrier,
Vonage, has a "softphone" feature which is in the computer; tying in with
a
headset/mike combo makes for better sound than the speaker and built-in
mike. If we had a reliable connection, we could be on the phone anywhere
we
had access, something which is *very* attractive to Lydia, who has 4"
Stainless Steel Hawsers for apron strings...
Back to the cat5, though, if you look at the URLs for Keenan, I'm
wondering
if what you're saying is that one uses cat5 to get signal to the masthead,
and powering the bridge is a coincidence of the cat5 connection from the
comptuter. Might one power a wireless bridge (which would then see my
laptop sitting on the boat somewhere) and put the signal up the mast to
the
antenna at the top? I'd sure rather have the bridge below than in a NEMA
box at the top...
Thanks again for the input (all who have contributed, too!).
L8R
Skip, refitting as fast as I can...
Morgan 461 #2
SV Flying Pig
http://tinyurl.com/384p2
"Twenty years from now you will be more disappointed by the things you
didn't do than by the ones you did do. So throw off the bowlines. Sail
away from the safe harbor. Catch the trade winds in your sails. Explore.
Dream. Discover." - Mark Twain