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Author Topic: WiFi antennas  (Read 1204 times)
KB1ONE
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Posts: 2




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« on: July 17, 2009, 10:36:55 PM »

CQ CQ CQ
BT
I am soon to be deployed to Iraq, as a chaplain's assistant.  I have a laptop that needs more wireless range.  I can build a suitable antenna, but really need help in getting a 50 ohm coax line into a USB port and operational.  My first radio had tubes, and this has me just a little confusicated.  All help would be greatly appreciated.
BT
73 to one and all
KB1ONE
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K9ZF
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« Reply #1 on: July 18, 2009, 05:25:13 AM »

I'm a long way from an expert, but the way I understand it, the favorite way to do this is to use a USB network adapter.  Then, instead of extending the feedline and raising the antenna, extend the USB cable and raise the whole network adapter.

There are also articles on the net for building a "cantenna" around the adapter to further extend the range...

Google is your friend...

Good luck,

73
Dan
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Amateur Radio Emergency Service, Clark County Indiana. EM78el
K9ZF /R no budget Rover ***QRP-l #1269 Check out the Rover Resource Page at:
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K9ZF
Amateur Radio Emergency Service, Clark County Indiana. EM78el
The once and future K9ZF /R no budget Rover
 ***QRP-l #1269
Check out the Rover Resource Page at:
<http://www.qsl.net/n9rla>
List Administrator for: InHam+grid-loc+ham-books
Ask me how to join the Indiana Ham Maili
WB5JEO
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Posts: 805




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« Reply #2 on: July 18, 2009, 05:31:08 AM »

Here are two interrelated links that should get you enough to deal with whatever adapter you have:

http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=18985

http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=18985

The parent directory has a ton of links to antennas, and some may have more on making the connection:
http://www.dxzone.com/catalog/Antennas/WiFi/

But I suspect the first two will give you enough.
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N4NYY
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Posts: 4799




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« Reply #3 on: July 18, 2009, 06:32:21 AM »

Linksys used to sell expanded range antennas that were faily cheap, like $30. They were quite a bit bigger than the usual antennas. I do not know if they still do. At that cost, it would be better to just buy them.
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KB1LKR
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Posts: 1898




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« Reply #4 on: July 18, 2009, 09:54:31 AM »

in addition to home built "cantenna" type cavity antennas, commercial yagi and parabolic type directional WiFi antennas are available, as well as Linksys's high gain omnidirectional verticals for their routers & access points.

If you extent your coax use as low loss a type as possible as losses add up fast at 2.4 GHz. You may also find you need reverse to regular "polarity" connectors (male connector w/ female socket vs. usual male pin) e.g. RP-SMA to SMA to interface w/ the FCC required "non-standard" connector on the router.
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OBSERVER11
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Posts: 657




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« Reply #5 on: July 18, 2009, 12:08:24 PM »

build a coaxial colinear antenna.

I made one using brass tube from the hobby shop and the center conductor and dielectric from RG8.

Put the antenna in a piece of PVC pipe, feed with RG8x.

Modify the WiFi router is you want, open the box, solder in a piece of RG303 (short piece) with a BNC and bypass that reversed SMA.
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N1DVJ
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Posts: 509




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« Reply #6 on: July 19, 2009, 06:05:29 AM »

There are higher power routers and access points available for export, but some of them can be pricey, and I'm not sure you could get one here to take with you.

Other than that, do you have control over both ends?  Or just your laptop end?  

In any case, for your laptop, get an external device.  USB with a cable to get the actual RF away and up.  

Also consider paying for something a big more than an external adapter for your laptop.  There are all kinds of hack sites on the web that have software to turn LinkSys WRT54G units into bridges.  You could set that or something like a WET200 up high and that might be enough right there.  

And as mentioned, antennas.  There are places that sell directional gain antennas for that work on WiFi.  One of the local clubs around here had an article they got over 900ft range.  Sure, that's clean conditions.  But then, so would you.  If you select your spot to link to the network, you can get the best conditions and then leave it.  If your setting a box up as a bridge, then just get a yagi for the link and aim it right at the network site access point.

And, maybe talk to whomever sets up the network, and get them to put their antenna 'up high'.  Or even add a second access point that is set 'up high' with a dedicated directional antenna aimed at your bridge or device.

But better do this now and quickly.  Over there is not the place or time to discover "oh, I need..." and find out it has to be shipped.

I'd set it up here and run it, just to make sure you can get it to work.  Then I'd box it up and ADD an additional cable and bot a directional and omnidirectional antenna to the box for 'donating' to the host site, just in case.  And maybe even take an additional access-point box, just in case you can set that high by itself with a directional antenna aimed right at your site.

Good Luck!

Mike
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KE6VG
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Posts: 297




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« Reply #7 on: July 19, 2009, 09:37:37 AM »

You will have to use a new usb wifi adapter and disable your on-board wifi connection. A simple way to get more range on-the-cheap is to make a corner reflector for the current antenna that comes with the adapter. When you purchase the new adapter get one with an external antenna, or external coax connector if you want to go with the cantenna route. On some laptops you can access an rf connector on the laptop by removing a bottom cover, but it is a PITA to route a cable out that way if you want to keep it portable.
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AA4PB
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Posts: 12892




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« Reply #8 on: July 19, 2009, 09:44:24 AM »

Don't forget that coax has a lot of loss at those frequencies. The wireless adapter needs to be located pretty close to the antenna.
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N1DVJ
Member

Posts: 509




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« Reply #9 on: July 20, 2009, 03:28:12 AM »

Yet another option is a WiFi repeater.  There are commercial units, but there's also a lot of info on the web on how to turn generic routers into repeaters.  

Just do a google on "WiFi Repeater" and you'll find lots of info.

Mike
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KB3LSR
Member

Posts: 297




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« Reply #10 on: July 20, 2009, 04:14:05 AM »

MFJ sells a yagi antenna.

http://www.mfjenterprises.com/Product.php?productid=MFJ-1800

$30 + Shipping.  with 15dB gain, it's much better than the "extended range" 7dB antennas LinkSys sells.

Good luck over there.
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WA3SKN
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Posts: 5494




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« Reply #11 on: July 20, 2009, 08:16:42 AM »

Just how much "range" do you need?
There are commercial units on the market, and you can do wonders with some aluminum foil and a box, but sometimes a wired connection is better.
Is there a network engineer you can talk to about this?
It may not be just "range" that is the problem.

-Mike.
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