There are two parts
to any successful WiFi
system - first is reception
of the signal from the shore based system. This is pretty much a factor of the type antenna
you are using.
- - Built in WiFi
in your lapbook/netbook/etc. uses an extremely small wafer type antenna
usually located at the hinges of the display. External antenna vary from "rubber ducky" omni-directional sticks of various "db" ratings. Then there are corner reflector and even highly directional "yagi" antennas that look like horizontal tubes.
- - The receiving antenna is rarely a limiting factor as the shore based systems involve rather powerful transmitters. What you see on your "signal meter" is normally just the strength of the shore based system transmission
- - What is the most limiting factor is the "return signal" - that is, the signal your computer sends back to the shore based system. Since WiFi is a "2-way" system, like a VHF radio
- your computer or antenna system must be powerful enough to broadcast a signal back to the shore based system.
- - Built-in WiFi in portable computers
average around 50 milliwatts or so - that is really a weak signal and as I am sure you have noticed you need to be really close to the shore based system be it in an internet
cafe or marina.
- - Over the last year or so, external "powered" antennas have really come up in the world with transmitting power increasing from a couple hundred milliwatts and up to as much as 2000 milliwatts for the pure USB powered systems. Besides the raw power increase put out by the powered antenna systems, their use of high "db" antennas seems to effectively also boost transmission
range - or at least they claim.
- - The original RadioLabs systems were about 400 mw; the Engenious EU362 is listed at 200 mw; the Alfa systems come in 500 mw, 1000mw, and 2000mw. Generally the more milliwatts the better, but you can also use antenna db to increase effectiveness. So a lower milliwatt system with a high db antenna may perform as well or better than a larger milliwatt system with a low db antenna.
- - Amongst the many variables overlooked is the fact that WiFi signals are very "straight-arrow" and must have an unblocked line of sight to the shore based system. Things like trees, aluminum
masts, light poles, etc. can all negate or hamper getting a good "lock-on". Boat masts are particulary vexing as they tend to move - swaying back and forth or rotating into or out of the line of sight path between your system and the shore system. Here is where antenna elevation can make a serious difference. Getting your antenna up high like mast
top or whatever, can get you a clear line of sight whereas an antenna down low has more obstacles in its way.
- - Getting your antenna up high introduces more problems of cables
and power losses due to cable length. (Nothing is ever easy). USB active extension cables
can give you up to about 80 feet (25 meters) of extension. But that introduces the problem of getting power to the "active" part of the cable. Since computer USB ports
are limited to about 500 mw is not uncommon for the computer to cycle the power on and off when the powered antenna wants too much.
- - So systems like Ubiquiti and others use outdoor rated ethernet cable to connect the masthead antenna system to your computer - and - use POE (power over ethernet) power supplies to keep the system running. The computer cannot put out enough power through the USB port to do the job. This solves a lot of problems and the systems work quite nicely.
- - Other systems use auxillary USB hubs powered from a separate power supply to get the "juice" to the antenna system. Data Alliance has a lot of Alfa system stuff and some rather long active USB extension cables. Antenna Cables: Use USB Cable as alternative (if possible) for More Gain
- - Bottom line, it is normally not so much which brand of WiFi antenna system you use, but the components in that system that make the difference - not to forget environmental obstacles to your line of sight requirements.
- - We have had very good performance from RadioLabs systems including their Captifi 1000mw bulb system - which we still use. But with most all things - computer - everyday or week something new and "better" comes along. So we are migrating to a permanently installed masthead system with supplemental power supply. Remember computer USB available power is just not enough for the big systems.
- - Standing back and looking at various cruising boats these days - more and more they are starting to look like NASA antenna farms. I remember when sailboat masts used to be used for hauling up just sails
rather than also a farm of antennas.