Bexley Link

Brighton Central AP Gets an Upgrade

Admittedly more due to low reliability than anything else, we have given the Brighton Central Wireless Access Point an upgrade, simplifying it's structure somewhat, with a view to never having to touch it again. The goal is simple, but there are a lot of design considerations behind it all.

The first thing that we did was raise the mast three feet, changing it's construction from it's original double reinforced PVC pipe construction to metal pipe reinforced by the original structure. It's amazing how windy this location is, and we have taken every precaution possible to ensure the security and safety of the equipment that we have affixed on high.The bottom of the mast is now eight storeys, three feet and a bit high - an outstanding radio location with 360 degree views.

Next, we prepared the new equipment housings, which had to be designed to exist in the harshest of environmental conditions from torrential ran and regular cold gale force winds to 45 degree plus ambient temparatures in direct sunlight during summer, coupled with hot winds.

We chose to join three IPV rated equipment cases together with water pipe on a set of rails making one assembly of it all, that also minimises conducted heat from the concrete rooftop, whilst providing air ducting for cooling and keeping all the wiring internal. We sealed the pipes with time expired aircraft sealants (PR1440 A&B 1/2) that were to be thrown out otherwise. The centre box ventilates fan forced heated air downward (Ok we are resisting convection here but it was easiest to build with water ingress in mind), whilst the two outer two boxes have filtered fans drawing air in from their protected inner sidewalls. The intent is to have the outer boxes slightly positively pressurised to minimise water ingress, and any ingressed water out via the drain pathes. Yet to be mounted above the boxes is a sturdy metal cover that will shade them from radiant heating

The centre box houses the power supplies, the terminal blocks, an ethernet switch, and the exhaust fan (which is larger than the inlet fans), whilst the outer boxes house the access points, providing the greatest physical separation between the RF sources and hence the lowest desensitisation of competing receivers. This design is a compromose as metal enclosures would have been superior, but when the budget is limited, plastic boxes with sensible spacing work just fine. We have found that so long as the channel spacing is opposing (ie channel 1 and 12), that AP's can be mounted quite close to each other with minimal desensitisation. We keep the closest channeled units apart as much as possible. The incoming link is 5.8 GHz 802.11A, which doesn't upset 2.4 GHz at all, so it just goes wherever it fits best.

The power supply will be a work in progress, as currently it's 12 Volts supplied by Power Over Ethernet (POE) from the floor below, with a 7.2 AH Gel Cell as it's UPS - which is currently good for about 8 hours mains free running, which isn't enough and requires the battery to be by the power supply due to copper losses up the POE supply. We are currently experimenting with solar power - not because it's cheap (IT'S CERTAINLY NOT), but moreso to make the network independant of conventional infrastructure, which is the driving ethos behind the whole network.................Anyways, the 12 volts is converted to a five volt rail from 12 volts by a switch mode regulator (less heat and most efficeint but sadly more expensive than a linear regulator), to power the switch and any D-link equipment that we may ever want to play with.

The Access points for sydneywifi.net/brighton/north and sydneywif.neti/brighton/south nodes are each Linksys WRT54G access points running Sveasoft Talisman software at maximum power output. Each WRT acts as a router, minimising network traffic across the network.