LisaPhifer   10 pts.  |   Jul 25 2005  2:49PM GMT

Directional antennas focus a transmitter’s output power into a narrower field. In free space, that makes radio signal travel farther. When obstacles like walls are present, the power delivered to the near-side of the wall will be higher with a directional antenna than with an omni antenna. If the wall merely absorbed RF energy, a higher-power signal would indeed have a better chance of propagating completely through the wall.

However, all walls are not equal. Some surfaces (like metal) reflect RF instead of absorbing it. For example, a window covered by steel blinds will reflect signal, while a stucco wall containing diamond mesh both reflects and absorbs signal, depending upon RF frequency (wavelength). This USC research paper describes attenuation measurements taken through a wide variety of building materials and radio frequencies:

“www.am1.us/Papers/E10589 Propagation Losses 2 and 5GHz.pdf”

Check out the measurements given for brick, stucco, and cinder block. I have not seen any published specs for adobe walls, but your walls probably contain some type of wire mesh inside them, and of course nearly a foot of mud. A high-gain directional antenna might be somewhat helpful, but ultimately may not provide sufficient coverage where you actually want it in the distant apartment. You may have better luck pursuing another alternative — for example, Ethernet over Powerline  <a href="http://www.homeplug.org" title="http://www.homeplug.(" target="_blank">www.homeplug.org</a>), or connecting WLAN bridges to directional antennas placed just outside windows, aimed at each other.