Category: Farallon Islands

Ubiquiti Rockets and a 50Km Path Over Water…

FarallonsThis last fall, we put in a 50Km 5.8Ghz link from the center of San Francisco (Twin Peaks) to the South East Farallon Island lighthouse using Ubiquiti Rockets. At first the link was unusable. This was mainly due to the fact that the long distance and shooting over water causes the received signal to vary wildly. This cased the radios to frequently and rapidly try to change the MCS (modulation scheme) and would make the link very lossy. Here are some settings I had to settle on to get the links to work.

  • Do not enable auto-negotiate for the signal rate on long links. The radios will auto negotiate data rates when the receive signal level changes. This will momentary drop the link while the ends sync up. If the signal is bouncing frequently this will make the link pretty lossy or not usable at all.
  • Long links or links that are being interfered with will likely have problems with modulation schemes that have an amplitude component such as QAM. If so, use a modulation scheme that doesn’t have an amplitude component like BSFK where you can leverage “Capture Effect“. This would be MCS0 (1 chain) and MSC8 (2 chains).
  • Fix the distance of the link to about 30% over the calculated distance. The auto-magic calculation that AirOS does typically is wrong with long links.
  • Turn off AirMax on Point to Point links. AirMax is used to manage multiple clients on one AP more fairly. Not needed for P2P.
  • Use as narrow of a channel you can support for the bandwidth you need. As per the AirOS manual…
Reducing spectral width provides 2 benefits and 1 drawback.
  • Benefit 1: It will increase the amount of non-overlapping channels. This can allow networks to scale better
  • Benefit 2: It will increase the PSD (power spectral Density) of the channel and enable the link distance to be increased
  • Drawback: It will reduce throughput proportional to the channel size reduction. So just as turbo mode (40MHz) increases possible speeds by 2x, half spectrum channel (10MHz), will decrease possible speeds by 2x.

The Farallon Islands’ Web Cam

For some time now, as someone has had an objective to get broadband in remote areas of the world, I have been looking at some lonely islands 50Km off the coast of San Francisco known as the Farallon Islands. Back in 2001 or so, at a past Bay Area Wireless Users Group meeting, Simon Barber, suggested that we hook the island up as the main island is staffed and they just had basic two-way radios for communication to the main land. For various reasons it never quite happened until this year when a number of different interests and funding fell into place.

I was introduced to folks at AirJaldi who were looking for locations in the Bay Area to test their radio deployments. I have access to a number of hill tops around the Bay Area and suggest to them that we put a link into the Farallons. I called US Fish and Wildlife and was pointed to the Point Reyes Bird Observatory as they do the day-to-day operations and science on the islands. At the same time I reach out to them, the California Academy of Science was looking to put a high-definition web cam out on the island to stream back to the public. Bingo, we have funding and very interested parties that want fast bandwidth to the island.

After much work in planning, purchasing and deployment, the Farallon Cam was turned up a couple of weeks ago.

It hasn’t been smooth. Some of the problems encountered have been links failing due to interference or hardware failure. This has caused the stream to be down more than we wanted to, but it did show for a small budget, that consumer grade unlicensed radios can provide decent bandwidth tens of km to provide the infrastructure for applications like streaming video, voice, data, etc.