Bandpass filter: hardware or software better?

Help!

I am a new member. I am having trouble getting online with wifi
at home. I can use the mini-card or the USB draft n adapter, no
problem when I am at a coffee shop or such other places, but
when I'm home, problems!

First, I know, using wifi software that there are some available
links, but I get the message that the signal is too weak. The ones
worthwhile are encrypted. The others with no security have
signals where the noise is usually greater than the signal strength.

I spent money for a 802.11n USB Engenius adapter, cable &
pigtail and a 15dBi 10.25" diameter, hi-gain antenna. I was
wondering, before I sink another $70 to $100 for a bandpass
filter for hardware to reduce noise, or buy a software program
that will filter the signal to reduce noise - will this help?

Do I even understand the problem?

I do have obstructions like trees in the way, though I'm on the
2nd floor and a new condo is going up across the street, and
probably looks like a restaurant next door (maybe wifi there?).

Netstumbler routinely finds at least 10 wifi sources, and Inssider
by Metageek also finds 10 or even more. But those programs
don't let me connect.

Basically, do bandpass filters work? Is the hardware or software
better to buy or am I wasting my time and money?

Ed