2 Computers...1 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)

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

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?

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.

The combiner is $48.

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.

Consider a WiFi repeater go to

While at it, if you have Cell phones, consider ALSO adding a similar Cell-phone repeater at

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

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!

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.

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.

internet

seems like a trivial prob to me. if you dont want to power up both notebooks at the same time, then take out the card from notebook 'A' and put it into notebook 'B' when you want to use 'B' only!!!

No doubt that would be a easy solution if I NEVER wanted to have both running at the same time, but that's not the case.

Repeater/extender sounds ideal but you would need to find model number of existing AP to be ascertained that you'll get one that will work with it. Then you would actually extend the system so your neighbors might benefit too and become the dock hero - at least until you sail off into the sunset.

Has anyone here (not connected with the vendor) tested these "Signal Seeker" USB-connected flat panel devices and determined whether they actually give better performance than cantennas, etc., as claimed?

I'd be happy to evalute a pair of them... with the understanding that I keep the pair when the tests are done.

I'm not the moderator (does this group have one?), but I'm the one who asked, and I'd be glad to take one and test it against the adapters I have available (internal Belkin F5D7000 with cantenna; USB Netgear WG111) and report my comparative results--I'd return the Signal Seeker if it does not work better than each of those, or pay for it and keep it if it does. If you accept this offer, please e-mail me for mailing address.

Big Cheese, Jeff. Moderator, Peter Pan. The group settle on anything? Not likely. Best tester? Jeff or Floyd, but I don't think they work for free for a commercial endeavor. Who would test the thing and make it stop looking like you are the only one who likes it? Me.

That reminds me. Did you ever get the test results report? From the eBay store page:

Q: exactly how much of a DB gain does this give you? A: We are waiting for the report to come back. But I know it will keep up with a 14 db panel antenna and a 500 mw amplifier. So I am guessing around min 26 to 30 db gain to the computer.

How about the specification sheet? Q: I have a local wireless computer networking business here in the boonies 2 hours west of Chicago. But i am interested in your device. Where can i get full specs on it, including transmit power, ability to operate with linux drivers, etc? A: We are in the process of putting a specification sheet together. I know that it can keep up with a 14db panel antenna plus a 500 mw amp. Only have drivers for windows. But will be adding them.

I didn't know antennas required Windoze drivers.

It's not very difficult to do relative gain measurements. (Absolute gain is a challenge). Use a reference antenna, with a known gain, and compare signal strengths with either a client radio with signal strength indication, with an external attenuator, or with a spectrum analyzer. The only real trick is to not do it on a roadway or across a rooftop to avoid ground reflections. Over a canyon or plowed field works nicely. Try to get both ends at least 10 ft off the ground.

Once you have a setup that yields reproduceable results, you can easily measure vertical and horizontal -3dB beamwidth and patterns. The problem is that the pattern will not look anything like the computer generated simulations due to construction variations, reflections, VSWR, measurement errors, and junk pickup. However, it's better than nothing.

Measuring VSWR from 2400.0 to 2483.5 is easy with a directional coupler, sweep generator, RF detector, and oscilloscope. You can build a crude but functional directional coupler out of some semi-rigid coax cables. The signal source is a problem, but I have some tricks that might work. RF detector and scope are common.

I'm not at all interested in becoming part of what I'm guessing is going to be a legal problem. I do evaluate products and write copious and detailed reports with recommendations and analysis. I charge quite a bit but less than a professional lab with lots of test equipment.

In all cases, I sign an NDA (non-disclosure agreement) where all results and equipment are property of the manufacturer. I am not allowed to release any information on what I've found. That's why I can't post performance measurements on some wireless devices. The numbers belong to my client. I've also been very lucky in that my results and testing has been used by the client in an honest manner. This is not universal as some of my friends and competitors have had their test results edited, tweaked, or butchered, by the client.

Anyway, it's all academic because I just picked up a design project, need to fix the house a bit, wanna spend some time away from computahs, it's tax time, and wanna do a vacation. For the price of an antenna, no thanks.