I have an off-grid home. My closest neighbor and I use two-way satellite (DirecWay). Now we have a third neighbor moving in who was talking about getting the satellite connection. I said that was nuts :-)
Another neighbor, just about exactly 1km away over open water (foggy at least 60 days a year, if that matters) has cable access. While she can't legally share that, I have no problem paying the cable company for a business connection which we _can_ legally share.
I want to set up an access point where the cable connection is, with a directional antenna to us. The three houses are within 15 degrees from that point. Then, at each "client" house, I want to put a directional antenna pointing back to the base, connected to a repeater, so that the computers in the client houses have wireless access via the repeater.
The real problem is that I'm confused by much of the terminology used and I'm not sure what I'm really looking for. Using D-Link as an example, just because it was easy to find, not because I know enough to want to buy them :-), it would seem I should be able to use:
- DI-524/624 at the base station, connected to the Cable and external antenna
- either a DWLG710 range extender or a DWL-G700AP as a repeater. Seems like they'd both work, but the AP has more capabilities and costs less!
Am I on the right track? And is that fog going to be a problem?
Derek, I don't think you will get 15 degree coverage over 1km, As I learned the hard way a 15db / 8 degree cantenna goes a lot further than a 20db / 30 degree panel antenna. I guess you have to divide the power over the area covered. I would reccomend several cheap AP's using non adjacent channels all plugged into a hub or router at the base station with seperate cantenna's aligned for each client (put it in bridge mode if client is a network vs an individual machine- you will also need cantenna on client end to insure hi bandwidth connection. it might be cheaper to use a pair of dish antenna to bridge the lake and then redistribute from your side.
Well, we'll see that when my test equipment arrives :-) I've got a couple of 14dBi/20degree antennas to test with. My brother-in-law thinks it'll be no problem, but that's one of the things I want to be sure of.
It might even be necessary. My two neighbors are very close and I'm not certain the one (who _is_ conveniently line of site to all the buildings) doesn't block the other from the cross-lake line. If a single antenna at the internet end could serve all three clients, the centremost house would probably be in the Fresnel zone of the other house.
Look into the Linksys WRT54G. It has some big advantages for what you're trying to do. It can run on anything between about 4VDC and
18VDC (negative ground). Using altenative firmware from Sveasoft, you can configure it as a router, access point, or client device. It will do WDS repeater bridging.
formatting link
DirecWay isn't all that fast. There really isn't that much bandwidth to share. Two of my customers have these with about 3 simultaneous coputers. It's a battle when everyone is on at once. The headache is the upstream bandwidth which averages about 40Kbits/sec and is easily saturated.
Cable is far better bandwidth suitable for sharing.
15 degrees is not impossible but difficult. A 14dBi panel antenna will have about 30 degree -3dB beamwidth which should work. You don't want to get a 15 degree wide antenna as the stations at the edge will probably be marginal. Instead of a repeater, I suggest either of the following approaches.
Use WDS (wireless dispribution service) to build to store and forward network system. I has all the advantages of a repeater, plus you can plug computahs into the WDS radio to "tap" off a connection. WRT54G is perfect for such a system. Essentially, each house forwards to the next house. The problem is that every time you store and forward repeat the data, the maximum bandwidth gets cut in half. See guesswork on bandwidth below.
Install the WRT54 in an outdoor box on top of a pole and run CAT5 to the computers. No need for power over ethernet at the WRT54G will run on just about any DC voltage from 4.0 to 18VDC. Just connect
12VDC, accept the copper losses, and it will work. This is generally simpler, easier, and probably more reliable.
No comment on range extenders and repeaters. Well, maybe a small comment. I think they suck, work only in about half the systems, are incompatible with much of the available hardware, and chop the available bandwidth in half.
Fog will not be a problem at 1km. However condensation on any outdoor electronics will be. I've had to coat my boards with various Humiseal products to keep them water tolerant. Perhaps a heater inside the box to raise the dew point will be necessary.
My guess(tm) is that at 1km (0.62miles), you'll end up with a 19dBi dish antenna at the client end and a 14dBi panel at the cable modem end. With +15dBm tx power output, about -85dBm rx sensitivity, and
4dB cable losses at each end, you'll get a fade margin of about 25dB, which is more than adequate for the link. My guess(tm) is that you'll end up with a fixed connection rate of about 12Mbits/sec OFDM. That will give you about half that in thruput. The first WDS bridge will get the full 6Mbit/sec thruput. However, the 2nd wireless hop will only get about half that, and so on. Methinks that's adequate. If you want more bandwidth, get a 24dBi dish instead of the 19dBi, and increase the connection rate.
Fire your brother in law. A 14dBi antenna with a 20 degree -3dB beamwidth would be a yagi. In my never humble opinion, this is a terrible choice. The signal strength falls over VERY rapidly at the
-3dB points. Even though you allegedly lose only -3dB at the end points, the slope is so steep that even the slightest misalignment will be fatal.
Here's some sample beamwidths extracted from random datasheets.
Type gain -3dB Beamwidth dBI degress patch 13 38 yagi 14 30 planar 13 25 dish 15 19
This chart for a yagi may also be of interest: gain -3db beamwidth dBi degrees 8 60 10 40 14 30 16 25
See my previous posting. Methinks that would be best. A solid dish to dish link across the lake, and then redistribute using WDS repeaters.
You may have one potential problem with the cross lake link that's unique to microwave over water. There will be two paths. The direct path between antennas and the bounce path off the lake. They will arrive at slightly differnet times at the destination resulting in self-interference also known as multipath. OFDM is very good at eliminating these effects but is not perfect. There will be times when the RF signal cancels and there's no signal to work with. The ugly solution is to setup one end of the link so that the antenna can be raised or lowered. I use cast aluminium hand rail connectors for the purpose over a pole/pipe to raise and lower the antenna assembly. After a bit of tinkering, the optimium, or least disgusting location can easily be found.
Ok, time to get irate.... Would you kindly replace "very close" with some real numbers? I'm a big fan of calculating before I build and find it difficult to insert "very close" into my spreadsheet.
It might be possible to run CAT5 or coax between houses. I've broken the cable length rules many times and know most of the tricks. You can go about 1000ft of CAT5 or RG-6/u (yeah, I know it's 75 ohms) at
10BaseT-HDX speeds without any difficulty. You'll get about
6Mbits/sec thruput. I've posted details previously. Please advise if interested.
On and off. I wish I'd read it _at all_ before I went off-grid :-)
Cool, but not necessary. I'm off-grid, but I do have AC - and plenty to handle a wireless device.
However, that's nice.
Tell me about it (oh, you did :-) ). I tell everyone who asks that it's only a solution for people who have _no_ other solutions. At the time I installed it, I didn't
The difference is what? That's my problem. I don't have a clue what the wireless manufacturers are selling when they say "repeater". Can you point me to some links? It's especially difficult when I go to sveasoft.com and they tell me their firmware has "WDS/Repeater mode"!
I thought that's what the repeater was supposed to do.
That's not a huge issue. I want to be able to promise better speed for less cost than Direcway for each of three sites. I don't think that's hard :-) (for those who don't know DirecWay, it's usually considered to be approximately ISDN speed once everything's taken into account - it can be much faster for large downloads, but latency kills www access).
As would the WDS, right? Half the bandwidth is just fine :-)
Hey, I don't have a problem with that - but my wife's attached to him, so I have to have cause :-)
LOL. I always hated "IMHO"!
OK, you've lost me again. You're saying 30degrees, and I only have to worry about half that. Where's the problem?
Yeah. I was afraid of that. I get a whole lot of electromagnetic radiation off that pond - I use photovoltaic panels for power, so I know there's reflection, I just have no idea how that works at wifi wavelengths.
otoh, I'm a fan of experiment, rather than spreadsheet. Tomorrow (I hope), I'll take my two antennas, an AP and a computer, and try them out from the base station in a direct line to my house. Then I'll try aiming the base antenna midway between the client houses. And if that works, I'll see what I get at the problematic house.
"Very close" is as close as I can say. I don't have a measurement for angle and I don't _know_ how close is too close, either in raw distance or angle.
If it comes to that sort of thing, it just isn't even worth trying to help the neighbors out. If I can't work a wireless solution that includes them, I'll do it point-to-point for myself.
Been there. I had a 200ft aerial run of RG-6/u on top of a mountain at a radio site. Worked just fine until mother nature delivered a nearby lightning jolt. Blew up a DLink DI-604 and two Milan/Digi
10baseT to 10base2 media converters. So, I replaced the router, repaired the Milan converters, and promised to "do something" about the lightning problem, some day, maybe. A week later, another storm blew up the replacement router. At that point, I buried the coax underground, inside some black plastic pipe and haven't had a problem in the last 2 years.
You mumbled someting about a 14dBi gain antenna with a 20 degree beamwidth in your 2nd posting. If you're trying to connect to two stations 15 degrees apart, you cannot use a 15degree beamwidth antenna. That's because the gain fall off at the -3dB points is rather sharp. Even the slightest misalignment will be fatal. I think
20 degrees is not enough. 25 would be about right but 30 is the closest available beamwidth.
It's a bit different. You don't get cancellations and reinforcements with ordinary non-coherent light. If the sun generated only one frequency of light, you would see interference bands (interferometry) and have cancellations and reinforcements. Well, 2.4Ghz is basically coherent spectra and does have the cancellation and reinforcement effects.
Did you notice my domain? LearnByDestroying.com You don't really understand anything until you've broken it.
Well, I can calculate what you will get if I knew the details on your equipment. The acid test for a fixed installation is how much attenuation you can insert in one of the coax lines and still have things function. That's roughly your fade margin. 10dB is the absolute minimum. 20dB is doing good.
Sigh. 50cents will buy you a protractor. I have a marine sextant, but that's kinda cheating. Piece of paper and some drafting supplies will also work.
A WDS repeater is a combination access point and repeater. It has to be the same chipset at each point in the repeater chain so don't try to mix hardware. The "range extender" type of repeater is quite different, but is also chipset specific. There's quite a bit of configuration involved in setting up the WDS repeater with the advantage of having some control over which data gets repeated and to where. The range extender just retransmits everything it hears with a specified SSID.
No. The "range extender" type of repeater cannot handle a directly connected CAT5 cable to the device. The WDS type of repeater can do that.
Yep. All these repeaters (and for that matter, all the wireless hardware) is simplex type of operation as opposed to full duplex. They can only talk or receive, one at a time. The result is that the repeater has to wait until one end of the link does its thing before it can retransmit the packet. That results in half the thruput.
Unfortunately my Cat5 is direct burial, and already in the ground. The other house isn't currently in use, so it's not clear anyone cares if I fix it, so I get some time to contemplate my options. 8*)
Right, that's what I have available right now. If I can get a good link across the pond point-to-point, with those, then it would seem that I should be able to get links to all three houses if I have a 14dBi / 30 degree antenna, then.
OK. That's working for me :-)
Got it. Thanks.
LOL. I hadn't noticed.
Knowing the actual angles and distances does nothing for me if I don't have a clue how close something has to be to be in the fresnel zone.
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