How to Get a better signal, How to Improve Your WiFi Security
Troubleshooting Your WiFi Security
Tips, DIY antenna, build your own antenna
Radio Frequency (RF) is not a simple as it looks, many complex parameters are playing against you.
As I am not a RF engineer, so I'll try to keep it simple, just for the rest of us.
WIFI 101
Your WIFI is basically a radio, it transmits radio waves between the router and your computer. WIFI was not made to transmit data over very long distance, it's "fragile" generally speaking, a lower frequency carries better over distance but no so well as for bandwidth, the higher frequencies have a lesser range and are more sensitive to attenuation from solid objects (wall, trees , etc )
A 802.11b/g WIFI uses radio frequncy between 2.4 and 2.4835 gigahertz (GHz) (5GHz for 11a)
The 2.4 and 2.48 are divided in 14 "Channels"
The "Channels" are 22 MHz wide but only separated by 5 MHz, hence they overlap.
Out of those 14 Channels, only 11 are used in the USA, 13 in Europe and 14 in Japan
A little picture will clarify...
As you can see now, all channels overlap but 1,6 and 11 (in green) do not overlap.
If you live in a crowded area, (WIFI speaking) and everybody use the Channel 6, it will create a lot of interferences. Ditto if you are the only one to use 5, and everybody around you is on 4 and 6.
If you are in USA, only use 1-11. For Europe 1-13, and Japan 1-14.
When you ask KisMAC to scan Ch 14 in USA, you are almost listening to your microwave: Your common kitchen microwave use a 2.5 GnHz frequency. Avoid that, it may lead KisMAC to panic a little and hang out.
Noise To Signal Ratio (NSR)
Noise is the pollution. The lesser the noise, the better.
You can test your Channels, noise interference with a program called AirRadar. ( Shareware )With a simple test, Air Radar will tell you which Channel is better for you and which ones have the highest NSR
You can also use AirGrab, no Self-Test, but free and you'll be able to see your NS
Geting a better WIFI signal, Troubleshooting
Your common kitchen microwave use a 2.5 GHz frequency, hence try to stay away from a working Microwave.
RF (Radio Frequencies) will penetrate or bounce around object depending on the density of the object and on the RF frequency.
Best is an open line of sight, worst would be behind a lead wall. In between, you can move your antenna up or move away from those aluminum venetian blind.
Getting a Good wlan adapter (less than $39) will often resolve all your issues and boost your reception/signal
The output power of the Alfa is 20 times superior compared to your average Airport Card.
I improved by a Factor of 25 compared to my Airport Extreme.
Making your own signal booster (DIY Antenna) can be a 5th grader project and be done in 15 minutes.
How to Improve Your WiFi Security
This is no secret: WEP is weak and can be cracked very easily. Whatever is your password, it will take me between 2.7 seconds and 2 hours to crack it. The only solution for a safe WIFI is to not use WIFI.
Let me explain:
There is no "Safe: Safe is a Swiss Bank inside a SuperMax Prison inside the NORAD Command Center.
Safer is different: WPA is safer. Much safer than WEP, but has a vulnerability. It can be cracked.
In the case of WPA, if cracked, it's your fault: the password used was guessed too easily.
As a matter of fact, I am going to be very nice:
If you can find your password in this list, it's probably a very bad sign. So, look for file named "Rockyou list" and check it against your password.
After that, you have two solutions in hand: Improve your Password / Passphrase or use a Cable.
If you still want to go WIFI, then the next best step is to use KisMAC and Wireshark to see if someone has cracked your WIFI, or is trying to crack your WIFI. Yes!, you can tell ....
cable would be my very last choice. 
Better than the previous, but more expensive. About $30 for 8m feet, and you still have a loss. 
or a 
, I pulled a signal @ 15km with one of those babies :)
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