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Saturday, March 15, 2008

Long-haul WiFi - new developments

Returning to the WiFi topic, here is the new antenna development that I had promissed in the early post, once the dual "cantenna" design was finished.

The dual cantenna is quite efficient, as I realized by connecting it to reasonably distant access points (in excess of 200 meters, with many obstacles between, including houses). By verifying the antenna efficiency was the expected, I assumed that in better conditions the range could be far greater, by establishing a link between two antennas of this type or other type of optimal configurations.

However, I knew I could push it a little further, so I decided to buy a 12 euro 45 cm dish from a regular satellite TV system, and the materials to build a biquad feed. I installed the dish on top of the tripod used for the cantennas, and attached the biquad feed (built according to these instructions) to it:

Instead of using the SMC repeater I've used before, I decided to get my hands on two foneras with a fresh new version of OpenWRT and do a slighlty different setup: one of the devices would connect as client to the remote network, having the dish antenna attached to it. The second device, linked to the first through the Ethernet port, would be configured as Access Point and provide DHCP to the clients on the local WiFi network. The first fonera could additionally do NAT and have a few firewall features activated.

So far the efficiency tests have not revealed far superior results, most likely because of the low quality coaxial cable (RG-58) used for the connection between the antenna and the fonera.

This type of design could be ideal for building small weather stations where power is a significant constraint and some data needs to be periodically transmitted. Other application could be for surveillance cameras where the location of the camera could turn impratical the use of a wired link.