antenna-theory.com

[proguru]

Hi. I have a following USB WLAN stick with poor reception.
http://oi46.tinypic.com/20ucqo9.jpg

Is it a good idea to solder there any external wire as an antenna? What kind of DIY antenna do you recommend?

[bigSteve]

That meandered wire at the top of the picture is your antenna there (it also uses the overall ground as the other arm of the dipole).

Looking at it, this isn't a great antenna. Meandered antennas tend to have crappy efficiency.

As for do it yourself stuff, first I would recommend examining the circuit board and the components (inductors, capacitors) on there and see if any are damaged. If all looks good, then you'll have to guess and test. Without a Vector Network Analyzer (VNA - which is very expensive) you can't really tell what's going on with the antenna.

You could try different things like adding some copper tape length to the antenna (or trimming it a bit). Trimming can be done simply by cutting away part of the antenna. Extending it can be done by scraping away some of the top non-conductive cover lay and soldering some additional metal onto there.

If you want to try to do an external antenna, that may work too. Just disconnect the meandered wire completely (cut it away), and solder on about 1/4 wavelength of wire (any will do). 1/4 wavelength at 2.4 GHz is 3.1 cm.

To test if any of this stuff works, you'll just have to plug it in and see if things get better (try to come up with some sort of repeatable test setup - i.e. constant distance from whatever you are trying to communicate with, with identical conditions between tests).

That's about it