On Fri, 16 Jul 2010 18:11:53 +0700, Bruce in Bangkok
wrote:

You had mentioned, I believe, mounting a wifi antenna "on the roof".
What were you feeding it with? I currently have the RF to USB device
mounted at the antenna and the down feed is a USB cable however it
appears that a length of more then approximately 10 feet results in
deterioration of the signal at the computer, and I assume the other
way also.

I have seen USB cables with built in amplifier. Did you use these and
do they require an external 5 VDC source? Or can the computer power
them?

My understanding is that at this frequency the coax represents a
significant loss and so have used only 5 -,6 inches of coax from the
antenna to the USB - wifi adapter with USB the rest of the way.

What you want is an antenna coupled directly to a Ubiquiti Bullet 2 HP
or something similar. Since the WiFi adapter is coupled directly,
there is virtually no feedline loss. The output of the adapter is
Cat5 ethernet cable which also suplies the power via a
Power-Over-Ethernet injector (POE). Cable length can be up to about
100 feet with no impairment.

http://www.amazon.com/s/?ie=UTF8&keywords=ubiquiti