Originally Posted by svcambria
...You get to struggle with what kind of antenna, but most of them are pretty small. Mine is "directional" (works pointing in one direction with about a 60 degree aperture) and is about a 20 cm square, 3 cm thick, clamps onto a stanchion. Michael
Directional antennas, of course, don't work well when you're swinging around at anchor
. There's always a trade
off here. Your antenna will only transmit the power you feed it - the trick is making that power go in the direction you want. A flat "patch" antenna like Michael's will direct your energy into a cone but you'll probably still find yourself adjusting it often unless you're tied to a dock
. The angle of that cone depends mostly on the size of the antenna, so you should read the specs. A larger, higher gain flat antenna will transmit further but will have a narrower cone, so will need more adjustment.
A vertical antenna will radiate in all directions. I'm going to use a VHF
antenna analogy here, but it's the same for WiFi. The shorter, low-gain antennas will radiate a fair amount of power up & down as well as horizontally. That's why sail-boats have to use short 3dB whip antennas for our VHF
radios, while power boats (& also multihulls, that don't heel) can use longer VHF antennas with higher gain. Monohulls need their VHF radios to work even when they're heeled over, so they have to use low-gain VHF antennas. If you think of the radiation pattern as a donut (with the antenna sticking up through the hole) then the higher gain antennas flatten that donut, squashing it down so it doesn't radiate as much up & down but goes further out to the sides. This is probably a better type antenna for WiFi - a high-gain vertical that radiates in a thin horizontal plate & doesn't waste power up & down. Put it as high up as practical to get over obstructions. It won't work well while you're sailing, but that's probably OK.
BTW, antenna gain
affects both transmit & receive. A high-gain antenna will improve both the same amount. But getting a high power transmitter
won't help you receive any better (& you need to do both) so that's probably of limited usefulness unless you're talking to another high-power transmitter.
Also, at WiFi frequencies (1-5GHz) you will lose most of your power, transmit & receive, in your co-ax cabling
if you're not very careful. You either need very short co-ax runs, or very large cable like RG8 or RG213. The best configuration is to put your WiFi transceiver right at the antenna, even if that's up the mast
. Then run a long USB cable
to it, because USB is digital & won't suffer any signal loss (if you use a good quality cable). Of course, this means that everything must be waterproof.
David, I hope that's not too technical...