Netstumbler readings and gain of antenna

Hi friends,
I am an idiot in radio communication. I have a question related to linksys SRX wireless Broadband router and Netstumbler readings.

I have made a can antenna for wifi band. and I have a linksys usb adaptor too.
I Installed Netstubler in my pc and Netstumbler detected my USB adaptor. now I set up the broadband wirless router abt 5 meter away from usb adaptor and powered up (sorry, my room is only 5 mtere wide). Netstumbler detected the broadband router with a signal strenght of -50 to -30 dbm. now I removed the three antennas from broadband router and connected my own can antenna and directed to my usb adaptor. distance is same as before. Netsumbler now getting a signal strength of -30 to -5 dbm.

What does that means? my antenna is getting a gain of 20-25 dbi?
I really confused with the netsumbler readings.
Please help me.

Hi,

I wouldn't have too much confidence in the readings made by Netstumbler
because they largely depend on the accuracy of the signal strength meter
of the receiver involved. These measurements are intended for alignment
purposes only and will give you a rough estimation of the signal strength.
Comparison between two antenna's is possible but will give you only
relative results.
A well constructed can antenna will have a gain of 12 to 15 dBd. I use a
PAWDC24 grid antenna with a gain of 22dBd, and that's a big chunk.
Remember that RG58 cable will have a loss of approx. 1 dB/m at this
frequency, so keep your cables as short as possible or use two short
"pigtails" and a quality cable between the two "pigtails".
Try switching off the radio of the client and measure again with Netstumbler,
you should get more consistent readings without the spikes.

on1aag.