What is the longest range I can get with a WIFI antenna.?

Question

What kind of card should I use?
What kind of antenna?
I need miles of range.

Answer 1

With the right antennas on both ends, proper alignment (very finicky), and using 802.11b/g you can get several miles at a reasonable transfer rate. 802.11n will improve that (currently available equipment is "pre-N"), and 802.11a will do worse (higher frequency is absorbed more by the atmosphere).

But, you'll only be able to talk to the single system your antenna is aimed at, not the wireless system next door or in the next room. In the US, there are FCC regulations for the maximum power you can ever use for WiFi. The antennas concentrate all the signal in a particular direction, maximizing the use you can get from that power.

Caveats:

1) Any pig-tail used to get connect a WiFi adapter card to an external antenna will lose power. You can minimize it by using the shortest possible pig-tail, by using the lowest loss cable (that stuff gets pretty fat, so you may not be able to fit it in), and by using a properly constructed pig-tail. Professional construction is generally best, because casual soldering technique won't do it at microwave frequencies.

2) Higher power adapters will help some, but nowhere near as much as a good antenna set up (remember the FCC's max limits?) Senaeo-Engenius seems to make the highest powered adapters, overall.

4) Your software has to at least allow high power operation, if not let you set your adapter for it. And you should probably be using the most recent version. See your vendor's Web site. Windows software is usually not very flexible. If it doesn't do it right out of the box, you're probably out of luck. If you're using Linux, and you can find a driver for your hardware adapter, the Linux software will probably be a good deal more flexible. But lots of manufacturers don't support Linux very well, some only for some equipment, some not for any, and a few for all their hardware. See the Linux Hardware Compatibility Lists if you need to.

5) Better sensitivity adapters will help hear the station at the other end. this is a characteristic of the circuit in the adapter and of the antenna connections. The only thing you can change once you have an adapter is to make the antenna connections correct, just as for transmitting. After all, both send/receive use the same antenna.

4) Proper polarization matters. Antenna signals can be vertically, horizontally, or anything in between polarized. Mismatched polarization can reduce signal levels very substantially.

5) Obstacles matter. A forest or even a big tree, between the two stations will lose signal, not what you want. So will car traffic, cows, rain, clouds, hot air (really!), etc. Avoid buildings between the two stations; partly because the signal won't intelligently try to sneak between two closely spaced buildings. RF is dumb, though some swear it's diabolical. Try for the cleanest line of sight you can manage and watch the weather.

If you have to, you can build your own antenna. Pepperidge Farm Prioutte cookie tins seem to be good, better than Pringles as a matter of fact. But you'll have to do careful work, for misplacing something by a few hundredths of an inch will cause losses. And so will bad solder joints, or if you mount anything outside, rust and wind vibration also. Plans are available on the 'Net from any of several WiFi groups. Dallas, Seattle, NYC, and San Francisco are especially active.

But if you really need miles, and it's important, I suggest you consider something that's more likely to be reliable, like a modem at both ends for using regular old phone lines. Or DSL at both ends (may not even need a regular telephone line account to get it), cable, or even satellite 'Net access. If you can afford it, cellular phone data does work, but it's expensive, not as fast as other choices, and subject to the whims of cellular antenna installation and locations. WiFi over miles will be a real problem and pain, even after you get it working. And rmeember that it can be eavesdropped so anything you send can, in principle and to a large extent in practice, be overheard. You'll have to arrange for effective encryption to avoid letting others in on your traffic. In the wireless standards, WEP encryption is next thing to useless, WPA2 is much better (being 802.11i in effect), make sure you use it correctly at both ends. And you can apply your own encryption if you like. I'd suggest either PGP (or one of the compatible programs) or GPG wihich is compatible. READ the documentation, for there are lots of ways to misuse cryptography. All GPG and many PGP implementations can be freely downloaded.