Which Antenna should I buy ??

On 27 Jan 2007 05:58:28 -0800, "steve" wrote in :

You need to start by determining the angle of coverage you need. With a distance of 125 feet and a width of 100 feet, you need almost 45 degrees of beam width, which will limit the amount of gain.

That's a signal booster, and while that might help _sending_ to your wireless clients, it won't help on the _receiving_ from your wireless clients, and so probably isn't a good way to go. (A high-gain antenna helps on both sending and receiving.)

A better choice would be the 9 dBi HAO9SDP, with a beam width of 70 degrees horizontal and 65 degrees vertical. Minimize the length of the coax cable connection for best results.

Since a brick wall is hard for Wi-Fi to penetrate, wireless clients in the second building may still need antenna placements in windows or directional high-gain antennas.

"steve" hath wroth:

I think I understand what you're doing. You want to "illuminate" the entire 100ft length of the building from 125ft away. That's a very common configuration that I use for setting up wireless in large residential complexes from the outside. The only gotcha are where there are wire screens or metalized mylar on the windows.

I also would need to know the height of the building for what I have in mind, but I'll just guess the usual 3 stories or about 30ft ft. You're obviously in a college so we're going to do this as a math exercise instead of a shopping exercise.

Horiz angle = 2 * tan-1 (50/125) = 2 * 22 deg = 44 degrees Vert angle = 2 * tan-1 (15/125) = 2 * 7 deg = 14 degrees

So, what you need is an antenna with a horizontal radiation angle of about 44 degrees and vertical radiation angle of at least 14 degrees. This is commonly known as a sector antenna. It covers a wide horizontal area, but has limited vertical coverage. However, typical sector antennas are usually 90, 120, or 150 degree horizontal coverage, so that's not exactly going to work. It's also impossible to calculate the required antenna gain because you didn't bother to specify:

1. What equipment you currently have?
2. How far into the building you plan to penetrate?
3. What radios are at the other end of your "broadcasting" (laptops)?
4. What thruput were you expecting?
5. Are there any obstructions in the line of sight. In my experience there are always a few overgrown trees blocking the view. (Hint: Numbers, not prose). When you're ready to supply some data and more numbers, we can calculate the required gain using the procedure in:

A sloppy first choice would be whatever antenna has a 44 degree beamwidth in both directions. To keep it simple, a panel or patch antenna has a fairly symmetrical pattern that varies only with gain. Very roughly for panels: gain (dBi) -3dB beamwidth (degrees) 8.5 60 10 45 13 38 19 18 So, if you don't care about the wasted RF in the vertical direction, a

If you do care about the wasted RF, a sector antenna is more appropriate. These tend to be custom or home built as each installation is quite different. I suggest you look into building a Franklin antenna. See:

The problem with these are that the angles do not match your arrangement. The advantage to these is that you can concentrate more of your power into a rectangular illumination pattern (i.e. more gain). One of the examples has a 125 degree horizontal beamwidth, the correct 15 degree vertical beamwidth, and about 13dBi of gain. That will illuminate more of the area, at a substantial increase in gain, with a highly desirable reduction in vertical angle to prevent ground reflections and wasted energy transmitting to the sky.

Numbers and calculations first, then go shopping. Once you know how much gain and beamwidth you need, the choice of antennas will be obvious.

Superb answer, Jeff. I would just add that a trial antenna that's very easy to build might clarify the problems he might run into. I would suggest he put together a Biquad antenna

Chuck

Very Good point Ive been thinking so much about gettng the signal there not back.

Probably then what you would suggest is two HAO9SDP's and and a signal booster. eg. Router ----HAO9DP *********HAO9DP---Router(?? or somthing) Then have to figure out what to do in the building.

Wow,

Well a few additions, Building I suppose is 35 -30 feet high.

Well no college was about 30 years ago for me. Didnt have computers when I went to college.

Just a wireless us robotics router right now. Mostly doesnt work.

Prety much whole building but dont mind a few dead spots.

Not sure what you mean?

Hadnt that about this. Basically this is just for surfing. We only have a dsl line coming to the the school fo offices etc.

No its pretty clear.

Something someone said above which I wasnt considering was that the clients are going to have to send the signal back to the main building this sounds like I will need hardware at both ends. eg not just one antenna and expect laptops and desktops to reach it. Am I right in my thinking? So I would have to buy two antena's and other hardware for the residence. regards

On 28 Jan 2007 04:37:25 -0800, "steve" wrote in :

I'd start off with just one HAO9SDP installed on the first building for the wireless host (access point/router), and then I'd do a site survey in the second building to see what's needed for the various wireless clients to connect reliably. Some may be able to get by with a standard wireless setup. Others might need something like the Hawking HWU8DD Hi-Gain USB Wireless-G Dish Adapter.

Or something in between.

On 28 Jan 2007 04:45:52 -0800, "steve" wrote in :

Laptops with built-in wireless? Laptops with USB Wi-Fi dongles? Desktops with PCI Wi-Fi adapters? What kind of antennas?

A single DSL line may not go far when shared. My experience is that you may well run into problems of (a) bandwidth hogs [e.g., illicit filesharing] and/or (b) hacking [student A breaking into the computer of student B, or the administration, just for the "fun" of it]. Thus I strongly recommend getting a wireless router with (a) isolation [so students can only access the Internet, not each other or the administration] and (b) QoS (Quality of Service, so no one student can hog all the bandwidth). A good way to do that for relative cheap is to run DD-WRT firmware (properly configured) in something like the Buffalo WHR-HP-G54 (a good choice because of higher power and the ability to run DD-WRT firmware). Figure on having to spend a fair amount of time each month sorting out these issues.

That depends. A good external panel antenna on the host building may be sufficient for at least some wireless clients using standard wireless adapters, whereas others (e.g., at the back of the client building) may need high-gain antennas. Run a site survey in the client building after the host wireless is installed in the host building to see what you need for each wireless client. Your worst case is that you may need wireless repeating (WDS) in the client building.

"steve" hath wroth:

Ok, increase the vertical angle to: Vert angle = 2 * tan-1 (35/125) = 2 * 15.6 deg = 31 degrees That will be a problem for my recommended AMOS antenna. 44 degrees horizontal and 31 degrees vertical is almost symmetrical enough to use a common patch, panel, biquad, coffee can, or similar antenna. I would also recommend trying a biquad.

Sorry. Bad guess. However, you still get to do the math. Dust off your abacus or slide rule (I still use mine ocassionally).

Have you considered getting the students involved in this exercise? In the past, I was seeing professional installs contracted by the administration. Recently, I'm seeing a few student inspired and managed systems.

Purchase a router that works.

It won't work. You'll get reasonable penetration near the windows and into the rooms facing the outside but nothing in the interior rooms, hallways, or rooms on the other side of the building. 2.4GHz does not penetrate building structures very well. You mention the building is

It takes two to tango. You have a malfunctional SMC wireless router. What type of computers are going to be talking to this wireless router? Laptops? Desktops? Are they going to be able to use external antennas that can see your malfunctional SMC wireless router?

It's important because range varies with speed. The slower speeds will go furthur. You can also trade speed for reliability. My guess(tm) is that your DSL line run about 1.5Mbits/sec. Therefore, I suggest a connection speed of 6Mbits/sec 802.11g OFDM which will offer the most range. This would be a key component of calculating the whether this will work.

Yes. The clients will need a wireless device of some sort to connect to your malfunctional SMC wireless router. It takes two to tango. What John Navas was aluding to was that you should not use a power amplifier at just one end. It only increases the range in one direction. It doesn't help if you can't hear the return signals. Incidentally, such an amplified system is called an "alligator" or an animal with a big mouth and small ears. If you need more range, it should be done first with antennas, which increase the gain in BOTH directions equally.

There's also a realistic limit to how many users can connect to your system. It really depends on what they're doing. My rule-of-thumb is: 100 light web and email users 10 business users 1 file sharing user Think about how you're going to administer and police this system. I can supply details if interested. Hardware is the least of your problems.

Suggestions:

1. Find a wireless router that works.
2. Connect literally any directional antenna with a gain between 8 and 12dBi to the wireless router. Place it in the proposed location.
3. Find a laptop and do what's called a site survey. That's where you walk around and see how well you can connect in the intended coverage area. If you want to do it with some cool but pricy software, see: Otherwise, use Netstumbler or iStumbler to check for coverage.
4. If building penetration is difficult, give up on wireless, and do it another way. 150ft is not very far and can easily be handled with CAT5 or fiber optic cable. If you must have wireless in the building, sprinkle a few around the building and perhaps use wireless for a point to point backhaul.
5. If the buildings have a common CATV, phone line system or AC power line, then these can be used as an alternative method.
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Alligator , Good analogy. I may use it. I guess what you really want is two ducks, quacking at each other.

Im going to start with an antenna. Then do a survey and see how it looks. Then perhaps add more hardware. I will also encourage students to get cheap boosters for their computers. You know, plug in a usb cable and a little external unit they can move around.

I Agree the CAT5 is the best option and I have looked at this. Although its not the easiest to string cable to. I have never seen outdoor cable ?? This is something that I would like to work towards.

Thanks.

There are various forms of CAT5 that can be used. Buriable CAT5 usually has a shield, heavy rubber jacket, and is filled with yucky silicon gel to keep the water out. You can also get it armoured if you have a gopher or squirrel problem.

Gel filled "flooded" CAT5:

Lots's more. Do some Googling.

However, I cheat. I snake ordinary CAT5 through PVC conduit, flex black irrigation pipe, or if desperate, garden hose. We have a neighborhood wired/wireless LAN with almost every type of cable possible. There's coax cable (RG-6/u and RG-58a/u), aerial coax with a messenger wire, dual mode fiber, CAT5 in 1/2" PVC conduit (under the road), direct burial CAT5, and armoured CAT5 through the trees. If the surplus scrap dealers have it (cheap), I'll used it. It all works quite well. The biggest dangers are falling branches, squirrels, wood rats, and clueless neighbors bearing chain saws.