I too am searching for a way to connect get wifi for our get-away cabin in New Mexico from an AP at the telco about 1 mile away. I thought I might chime in with some things I have learned and would do in your situation.
Seeing that you have pretty much line of sight and great conditions, I would go wireless with two 2.4 GHz grid parabolic dishes. The higher the dBi on the dish antenna the narrower the transmit/receive area will be. In your case, you know exactly where you are shooting so I would go with the highest affordable dish, 24 dBi. I have found them reasonably priced at
Streakwave.com and
l-com.com. The shipping is what gets you on most sites I have found, but those two are reasonable (Have streakwave.com orders shipped to a business or work address -- it is considerably cheaper than residential, some dishes weights are not entered correctly either so it will show $90 to $100 shipping. It should be $15 to $20 for two based on a model I got a shipping estimate on to my house). One dish will mount at the barn facing your house and one will mount at the house facing the barn. Another website you can find wifi stuff at is
Fleeman, Anderson & Bird, Corp..
Most of the dishes I have found will mount on a 1 or 2 inch pole. A old DirectTV or Dish Network J mount that their dishes mount to appear to be 2 inches and that is what I will use to mount our parabolic dish on. In your situation, you will need two. You can probably pick a couple up off eBay for $20 or talk to someone who isn't using their dishes anymore. The key is little to no movement however you mount them.
You could use the old satellite dishes, but you have to nearly point them to the ground and measure out exactly where to mount the can on the feed horn. Given my tight tolerances and distance, I have chosen to go with a application-specific 2.4GHz premade dish. Also, the grid helps with less movement from the winds moving the dish versus a solid dish.
Like blueroomelectronics said, I would think you could use a gun scope on the end of the feed horn to get them reasonably aligned with each other.
You can then buy two Linksys WRT54GL. I usually buy them off Amazon.com. Right now they are $70 but they drop down to $50 often. Flash both routers with
DD-WRT. It is very easy, don't be intimidated if you haven't ever done it. They have a
guide that explains how to flash the router. You will probably get version 1.1 router. It tells you to just flash the standard on v1.1 routers, but the last one I received I had to flash the mini version and then the standard version to get it to work.
Depending on the version of the antenna you purchase, you will need a N-Type Male OR N-Type Female (Dish antenna side) to RP-TNC (WRT54GL antenna side connection) pigtail to connect the dish to the routers. I would suggest that you use LMR-400 coax for the pigtail and 50 ohm rated connectors. You can purchase them premade off eBay, l-com.com, fab-corp.com, etc. Be sure they are LMR-400 or higher and not RG6 or RG59. The cable and connectors needs to be rated 50 ohms, not 70 ohms. The antennas are rated at 50 ohms if you look at the specs. Wikipedia has a good primer over
coaxial cable and the attenuation lose in dB per meter of the cable. Given your setup, I would think the barns needs to very short - meter or two and the house maybe 7 to 10 meters. Your internet connection will plug into the internet (WAN) port on the router in the barn. The WAN port on the router in the house will go unused. Don't plug a computer into it, it won't work.
DD-WRT will allow you to setup a Wireless Distribution Service in which you can link the two routers together. No need for a computer running at the barn and the house for the internet connection to work using up lots of electricity. Just these two low powered devices. You may put the router inside the barn in an enclosure, preferrably waterproof, weatherproof and out of the sun. I have read where some people have mounted a fan in the router or in the enclosure to keep it cool. Youtube has some videos. You would think you could even splice off the power adapter to the router to power a fan inside the enclosure? Maybe use a used drysheet as a fan dust collector? Here is a
guide on how to setup the WDS on both routers. Basically this will be your receive and transmit equipment from the barn to the house.
tcmtech talked about equipment locking up and having to drive to reset it. DD-WRT has built-in keep alive functions that power cycle the router on sensed lost connection with the hosts/internet and at pre-determined intervals, i.e. every night at 2am.
Make sure you setup wireless security. Don't leave them open. At a minimum use WPA and never use WEP or open.
The routers feature a transmit power increase feature over stock power (28 mW) from anywhere between 1 mW to 251 mW. I would use this sparingly since increasing the transmit increases the heat on the internals and could prematurely shorten the life of the router. You can purchase one or two external amplifiers, such as this **broken link removed** (Model: AR-1105) which I found on eBay. I would try the setup without it before you purchase something you don't need. I might note that it has different end connections than the WRT54GL (RP-TNC). It appears to need RP-SMA, but I would double check. Each connection or adapter you use in the line of connections from the router to the antenna will cause some dB lose.
Once both routers are up and communicating, you can use a program called iperf to test the actual throughput from router to router for dish tweeking.
You can connect to the router in the house via wireless or wired LAN in jacks in the back of the router.
As far as costs, you are looking at ~$100 for the two routers, ~$120-$130 shipped for the two dishes, and the cost of the pigtails. Still less than one months service. You may pick up one or two spare WRT54GLs if it works out. I don't know how much longer Linksys will continue to make the WRT54G(L) series of routers.
I haven't tested this particular setup but I don't see any reason why it wouldn't work.
Someone can correct me what I have wrong as I am researching this as well.
PM me or post back on this thread if you have any questions. I will try to remember to check back since I don't haunt this website.