Ubiquiti Rockets and a 50Km Path Over Water...

This 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.

Airfields of Yesteryear

An older post of mine talked about looking back at history with the little geodetic survey benchmarks you see in the sidewalk and at the base of older buildings. Modern archaeology has always interested me and if you are interested too, there is a wonderful site documenting abandoned airports around the US named "Abandoned & Little-known Airfields". It covers the history and evidence left behind when general aviation was more popular and strange little military operations that were out in the middle of nowhere.

As I have just spent the last 25 or so years living in San Francisco, it was a surprise to find out about strips that I didn't know about such as the Bay Meadows Airport in San Mateo and the Marina Airfield next to Crissy Field in San Francisco. Marina Airfield was the first terminus of the United States Post Office Department Trans-Continental Air Mail Service.

Growing up in Fresno, I remember the remnants of Furlong Field just out Shaw Avenue. ... Good to see it documented here so it isn't forgotten as development has pretty much obliterated any trace of it.

Sad to see so many fields disappear with the wane of general aviation in this country. It is just too expensive for most to own or lease a plane and keep it up. Land is being sold to developers as cities can see better tax revenue with a shopping center than an air strip.