http://www.metageek.net/products/inssider/
Download inssider n scan your surrounding wifi channels.
It's available on PC and Android.
If you have a laptop or android device, when using the app/software try to move around to the spots you use wifi in your location. Eg. Sofa, bed, work table.
At those locations take note which channel are free from overlap. Sometimes it's better to be on the same channel as another weak AP, than on a free channel in between other strong APs as it causes non-cooperative interference.


General rule:
- Basically, the channel you select must try not to overlap / cross into another channel.
- Being on the same channel as a strong AP is better than overlapping between strong APs.
- However, if it's crowded and you must overlap. Try overlapping between weak APs.
- If there is a channel free from any form of overlap, that is the best channel to use.

After doing that, one really good way to test a channel is to ping your router address after selecting your channel.
Wireless performance varies and weak performance will easily be shown by ping times.

You must close inssider program when doing ping as inssider can cause high latency when it's open.
Then open command prompt ('cmd' at start menu search)
Type ping <192.168.x.x> -n 25
where x is your router address, same address you use for router login from browser.

Under really good conditions it should be constantly <1ms or not more than 3-5ms from my experience. 
Choose the channel that gives you the lowest yet consistent ping

If you have no wireless b & g devices, set your router to run wireless N mode only.
If you can run wireless N only, experiment with 40mhz setting on/off and and wmm on/off, see which gives you better performance.

Also remember to set wireless security to wpa2-psk only and AES cipher only. It's best for performance, reliability and security.

If you really want the best performance and stability you must read this:
http://www.dd-wrt.com/wiki/index.php/Advan...reless_settings
http://www.dd-wrt.com/wiki/index.php/Wirel...N_Configuration
The concept of these recommendations applies to most if not all routers

Router antenna position is important too. If i've not mistaken L7 uses a 5dBi or 7dBi antenna.

Generally, if you plan to focus the signal on the same floor, put the antennas vertical. If focusing upstairs, horizontal, the output pattern of antennas are in general something like this:


Sometimes the problem may be your laptop/pc wireless adapter itself or it's drivers.
Lastly with all that knowledge, if it doesnt work out or too much to handle... might wanna get rid of TM's crap and get something real.