2 Computers...1 Antenna?

I have access to wi-fi in my marina. On the boat I have 2 notebook
computers an a single external antenna connected to one PCMCIA wi-fi
card. Is it possible to both computers share a single antenna if I
were to buy another PC card and some kind of a Y adapter to split the
antenna?

What are you trying to save? The cost of an antenna? Won't either machine
pick up the wifi signal?


"Champ" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
>I have access to wi-fi in my marina. On the boat I have 2 notebook
> computers an a single external antenna connected to one PCMCIA wi-fi
> card. Is it possible to both computers share a single antenna if I
> were to buy another PC card and some kind of a Y adapter to split the
> antenna?
>

Want be able the access the web from both at the same time. Have the
one antenna mounted on top of the mast. Trying to save the cost and
hassle of installing a 2nd antenna and associated wiring. Why mount 2
when 1 will do?

'Want be able the access the web from both at the same time.'

hi,
here's what i'd do. connect to the wifi network from one notebook with
the PC card with the external antenna. now get a usb wifi card and
install this on the same notebook.
connect to the second notebook using ad-hoc mode and enable internet
sharing on the first notebook ( if win 2k/xp)
What this essentially does is that configures the ip address of the usb
interface on the first notebook to 192.168.0.1 and enables DHCP.
so the second notebook will get an ip address from the first and will
be able to browse the network/internet.
PS ive also done this with a lifebook running XP and an i-book (mac)

Thanks outbackwifi. That's one option for sure, but I should probably
have added that I'd like to be able to use either notebook
independently without having to having both powered up. (Wife has
hers, and I have mine at the nav station.) Needless to say, I'm not
too Wi-Fi savvy and maybe it's just not possible, but a simple
Y-splitter would be ideal. Of course I don't know if anyone even makes
such a thing. Any other thoughts?

On 6 Jan 2005 18:25:05 -0800, "Champ" <(E-Mail Removed)>
wrote:

>Want be able the access the web from both at the same time. Have the
>one antenna mounted on top of the mast. Trying to save the cost and
>hassle of installing a 2nd antenna and associated wiring. Why mount 2
>when 1 will do?

I can be done, I've done it, but you won't like what it takes to make
it happen. FCC rules and common practice do not allow for
synchronizing the two transmitters. Such systems are also not type
certified in such a configuration, making them illegal for deployment,
but we'll ignore the legal problems for now. We'll have a problem
with:
1. Both transmitters on at the same time creating intermodulation
products that generate spurious crap that trashes other services.
2. Isolation between transmitter and receiver overloads receiver.
3. Spread spectrum "hash" bleeds into adjacent channels and creates
interference on the receive channels.
4. Loss through the combiner.
5. You will not be able to use an antenna mounted.

The usual combiner is a Wilkinson 1/4 wave combiner, which has a loss
of about 1dB and an isolation of about 20-30dB. The 1dB loss is not
much of a problem, but the 20-30dB isolation is. That's not enough to
keep the transmitter junk out of the receiver, or to prevent
desensitization. Because the VSWR of most antennas and radios is 2:0
or worse at the band edges, the isolation will be at the lower end of
the scale (20dB) or worse. The adjacent channel junk is about 30dB
down from the peak power, so the receiver will need to handle:
+15dBm - 20dB -30dB = -35dBm
of inband junk. That's roughly the overload point of the receiver and
will just barely work. What's needed is are two isolating cavity
filters each tuned to the two (different) frequencies. Only $100
each.
http://www.hyperlinktech.com/web/band_pass_filters.php
Subtract another 2dB RF loss.

The combiner is $48.
http://www.hyperlinktech.com/web/sig..._2400_2way.php
(You would not believe how simple the device is inside).

So, if you wanna do it, you'll need to have the two radios on two
different channels, $350 in boxes, about $30 in connecting cables,
tolerate 3dB (half the power) additional loss, and make sure you have
a very low VSWR antenna, which usually eliminates anything with high
gain.


--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558

Champ wrote:
> Thanks outbackwifi. That's one option for sure, but I should probably
> have added that I'd like to be able to use either notebook
> independently without having to having both powered up. (Wife has
> hers, and I have mine at the nav station.) Needless to say, I'm not
> too Wi-Fi savvy and maybe it's just not possible, but a simple
> Y-splitter would be ideal. Of course I don't know if anyone even
> makes such a thing. Any other thoughts?

Consider a WiFi repeater go to http://www.vivato.com and check out the
VP2210 - Outdoor Wi-Fi base station
(uses the high antenna for Wi-Fi, and repeats on the boat itself).

While at it, if you have Cell phones, consider ALSO adding a similar
Cell-phone repeater at http://www.cellantenna.com/, so you can use
cell-phones at many places around the boat

I use both on the roof of my RV((up 12 ft)), and repeat the signal for my
laptops/PDA and cellphones inside.

outbackwifi <(E-Mail Removed)> wrote:

> connect to the second notebook using ad-hoc mode and enable internet
> sharing on the first notebook ( if win 2k/xp)

Depending on where the laptops are located, you might just run a crossover
cable between wired etherenet ports on the two laptops, and enable ICS on
the one with the WiFi.

Or get a wireless repeater. http://www.dlink.com/products/?sec=0&pid=18

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Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5

The crossover cable idea seems to be about the easist solution. The
newest notebook has an ethernet
card built in. I guess all I'd need is a 2nd PCMCIA ethernet card for
the 2nd computer and the crossover cable. This isn't that big a boat
and a 10-12' cable oughta do it. Since you said "might" just run a
crossover cable, is this a sure, proven thing? This will really allow
both computers to access the web at the same time? As you can tell,
this stuff pretty new to me. Thanks for all the info guys!

Champ <(E-Mail Removed)> wrote:
> The crossover cable idea seems to be about the easist solution. The
> newest notebook has an ethernet
> card built in. I guess all I'd need is a 2nd PCMCIA ethernet card for
> the 2nd computer and the crossover cable. This isn't that big a boat
> and a 10-12' cable oughta do it. Since you said "might" just run a
> crossover cable, is this a sure, proven thing? This will really allow
> both computers to access the web at the same time? As you can tell,
> this stuff pretty new to me. Thanks for all the info guys!

It does break your "don't want to power them both up" desire.
The computer in the middle does have to be turned on.
ICS absolutley does work. The crossover cable definitely works. Your two
laptops will be on a network together. you get very little control over
that link. The IP address is fixed. Fuss with it, and it will never work
again ;-)

But if you have to buy a PCMCIA card and the cable, then I wouldn't go that
way. I would go with a USB-wifi. I see them pretty cheap now.
I bought one for $49.95, with two $20 rebates, end cost $9.95. I carry it
in my laptop bag to set up adhoc networks to customers that don't have a
network. A lot of people have unused ethernet ports, but almost everyone
has a USB port. I use AdHoc or a crossover and ICS in this fashion to
reach the internet via dialup, so it ought to work for your case.

Since the other card's antenna is on the mast, there probably won't be any
interference, if the existing card's internal antenna can be turned off.
Otherwise, you can select the channel used on the ad-hoc part (between the
two computers), you'll have no control over the channel used by the distant
WAP.



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Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5