For once...a topic I can respond to with some useful input! I work
with wireless point to point devices on an almost daily bases for security
cameras and network access to remote
locations on the college campus I work
at. It's one of the reasons I haven't yet been able to do my live-aboard
dream....my main marketable skill just isn't in demand/I wouldn't be able to get a work permit
Depending on exactly what you're looking for, solutions for a WiFi setup are situational. One thing to remember is that you can only control your end of the transmission
. This means that just because you can see an AP, that doesn't mean you can connect to it. Seeing a periodic beacon and being able to receive a critical mass of the packets sent are two drastically different things.
That being said, without getting to the definitions and complex math, the higher the dBi of an antenna
, the more it can "see". It may be an oversimplification of how it works, but in general it's true. An antenna will have a radiation pattern, meaning the angle and direction that the signal that the antenna sends is the strongest when viewed at the receiver. I was going to attach graphs of radiation patterns, but they can be tough to read. Basicly, you have two main types of antennas. Omnidirectional, and directional (or Unidirectional if you prefer, although they're not truly unidirectional).
Omnidirectional is generally thought of as a single
line, straight up and down type of antenna. These are frequently called "rubber duck" antennas. For your purpose of connecting to the shore, these antennas aren't as useful. This is because they put out a 360 degree circle of coverage around you. Think of their pattern like a doughnut, with the antenna in the hole in the middle. Most access points in people's homes and businesses will be using this kind of antenna. A typical gain for this type of antenna is around 8 to 12 dBi.
Directional antennas can come in several flavors. The two main ones I use are flat panel antennas and parabolic "dish" antennas. These antennas are typically much higher gain, as they focus a large area onto a smaller point, thus scooping up much more signal from a single
direction. As opposed to the "doughnut" from above, think of these more like a laser beam shape...although that is overstating the tightness of their pattern. The down side to this type of antenna is that due to how tight the "beam" from this antenna is...as your boat rocks, they could point at their intended target, and then away. This is especially true if you mount them higher up on the mast
. You can find dish antennas with a 24 dBi gain for less then $100, and flat panel antennas with maybe an 18 dBi gain for the same price
I guess the best way to describe the antenna reception
is that the higher the gain, the farther away it can "scoop" signals from. The issue you will run into though, is that you will also "scoop" more noise
if you're trying to receive a signal from a transmitter that isn't pushing out enough power, as is frequently the case with a home wireless access point. "Noise" is the crap signal that shares the same or a similar frequency to what you're trying to receive. Basically it's anything that isn't what you want to receive, meaning it could be another access point you aren't trying to connect to. If your signal to noise
ratio is too far out of wack, you won't be able to talk to the access point as you won't be able to effectively separate the "good signal" you want from the "background" noise on a consistent basis.
So, for transmission
. The main thing I can tell you is to put your transmitting device as close to your antenna as possible. Coaxil cable is one of the biggest signal eating components in a system, both transmit and receive. The next thing I can tell you, is power. More is better. But there are hugely diminishing returns. Every 3 dBi of signal is a doubling of the power. So, a 1 mW transmitter is putting out 0 dBi, 2 mW is putting out 3 dBi, 4 mW putting out 6 dBi, etc....up to the FCC legal
maximum of 1 Watt which is 30 dBi, I know there are many geographical areas not covered by the FCC, but mine is. There are rules about antenna gain/power combinations as well...
So....I don't know if that helped answer any WiFi questions you have, or just created more. Typically, I will use the following:
Ubiquiti Bullet M2HP (or M5HP depending on frequencies desired)
Any 24 dBi parabolic grid type antenna, they can be found on amazon and due to the grid design have minimal wind
Or, if I'm looking for an all in one package for a shorter haul, I use a Ubiquiti Nano Station M. They have a lower gain and lower transmission power, but they're compact and cheap