Archived from groups: alt.internet.wireless (
More info?)
On 14 Aug 2005 19:52:16 -0700, juliuslr@gmail.com wrote:
>I just installed a mini PCI wifi (802.11b) card in my TP600X and also
>installed a pair of internal antenna routed just below the keyboard.
Ummm, most of the laptop internal antennas are routed up to the top or
side of the display section. It won't work very well with the
radiating part of the antenna down low, near the RFI sources, under
the shielded keyboard, etc.
>The signal received is very weak (one bar). So I disconnected that
>antenna pair and hook up a spare and route that one outside if the
>laptop. Same weak signal.
Good thinking. That should have made and antenna work better. Did
waveing the antenna around change the signal level? It's not the
greatest way to tell if it's working, but if the RF is coming from the
antenna, you should see a change.
>Looking at the antenna wire, it looked like a
>very small coax cable, terminated at one end on a small coax type
>connector (center pin and snap ring on the ground side. What bothers me
>is the other end. both the center wire and ground is soldered to a thin
>metal bracket. So how does this antenna work when resistance wise it is
>a short ?
Oh, that's easy. Any antenna that's 1/2 wavelength long is an open
circuit at the resonant frequency. That's about 6mm at 2.4Ghz. To
get 50 ohms, the coax cable is connected to a "tap" that's about
10-20% of the distance from the ground (shield) end of the antenna to
the grounded end point. There are also "slot" antennas, that are a
piece of sheet metal with a 1/2 wave slot and the coax connected
across the slot. Some antennas are "J-poles" which are either 1/2 or
5/8 wavelength long, with a 1/4 wave driven element. Everything is
grounded. There are also ceramic substrate tuned line antennas, which
shrink the wavelength dimensions down to miniature size similar to
what's used inside some cellphones.
Be careful with the u-FL connectors. They are very flimsy, do not
tolerate any abuse, and will break at the slightest provocation. If
your antenna assembly was not designed specifically for your
unspecified MiniPCI card, there may be a connector problem, or you may
have trashed the connector if you forced it. Did it go "click" when
you attached the connectors? That's a good sign that it fits.
Antenna for IBM laptop with some nifty references:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=5230419854
Looks like a J-pole antenna.
Installing an internal antenna in an IBM A31 laptop:
http://www.jordanautomations.com/tpa31-internal-wifi-upgrade.html
Ceramic antennas:
http://www.gigaant.com/
Some good stuff on antenna basics and theory:
http://www.gigaant.com/?id=246&lang=1&state=1
(see links in the right window).
--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
AE6KS 831-336-2558