Need a lot of Help with setting up wireless

On Thu, 7 Feb 2008 22:42:38 -0500, cliffjag wrote in :

Wirelessly? That would only be possible if one of them can be configured as a wireless Ethernet client bridge.

Wired? Then one should be configured as a wireless access point, not a wireless router.

It has to be clear including the fresnel zone, which is pretty big over that distance. If you're just looking through a small hole, that doesn't really qualify as clear line of sight.

Hard to say without knowing what's in the middle.

I would go with panel or dish, not yagi.

Just out of curiosity John, why is that?

I was just looking at a 2.4 Ghz Yagi, which are commonly used for cellular, and wondering why panels and dishes are more common in WiFi.

Steve

On Fri, 8 Feb 2008 11:39:52 -0800 (PST), seaweedsteve wrote in :

Less critical aiming.

There is no single answer, but rather the selection is based on the application.

Yagi are easily detuned by ice (a moot point in southern climates), but can have a radome. They have significant side and rear lobes (the severity depends on the antenna gain).

Flat panel antennas have significant wind loading, but are almost immune to ice build up (especially is faxed). They have excellent side and rear lobe rejection. Gain and pricing is comparable to a Yagi.

Dish antennas - the solid dish has significant wind loading, but that can be reduced with a radome. They have some minor spill over. Highest priced, but the highest gain.

BBQ dish antennas - Gain is less that a solid dish, but little wind loading. Price is comparable to a panel, half of a solid dish.

To answer your question.. Very few people use a gain antenna for a cellphone, but everyone uses it for 2 to 8 mile wireless broadband clients. Check all the supplies, how many do you see selling Yagis for WiFi...very few.

The above information is based on professional everyday experience where system reliability and profits are important. Not from some amature hack that recommends consumer grade wireless products for an occasional wireless link, and that doesn't have $50,000 a year set aside to play with nor $30,000 worth of test equipment.

Would you settle for somebody instead?

Any particular routers? Are they wireless routers? Are you adding a pair of access points to a pair of routers? Just what are you doing?

That range should be easy.

Ummm... Read up on Fresnel Zone diffraction. You need MORE than optical line of sight at 2.4GHz. See:

at 170 meters, you need at least 1.8 meters clearance at midpoint. Do you have this?

Well, since you didn't bother specifying what radios you're using, I can't really tell. I can calculate the required gain if I knew the tx power and rx sensitivity. Also the speed requirements. See the FAQ at:

for an example of a link calculation. If you need help, I'll need some numbers.

Sounds like a panel antenna might work. They come in various sizes and gains. However, antennas have 3 dimensions. Length, Width, and Depth. Is it a 30cm cube or sphere? Probably not. Could you supply the missing dimensions?

I'll assume that's connect speed. At 11Mbits/sec connect speed, you'll only get about 4Mbits/sec thruput. What manner of TCP thruput are you expecting?

That really depends on interference. Have you done a site survey with Netstumbler, Kismet, or a spectrum analyzer to check if the line of sight is not polluted with other 2.4GHz systems. Also, see:

for a checklist of interference sources.

Calculate first. Then spend the money.

Hint. How long do you thing a 2.4GHz yagi would be in order to equal the gain of a 24dBi dish antenna? (Answer is at bottom of this message).

Well, cellular is at 800/1900Mhz in the USA. That makes for a somewhat larger antenna. A dish for 900Mhz would just be too large. Many cellular yagis also end up in peoples car trunks for long range use when in remote areas. A dish just wouldn't fit.

There are two problems with a yagi that makes it a bad fit for Wi-Fi.

The typical yagi has lots of side lobes, which causes lots of reflections, and potentially picks up interference from the side and back. Panels and dishes have much less side lobe junk.

The construction of the yagi is fairly critical and complex when compared to the typical panel and dish. In fact, the dish can be fairly sloppy, and still work. Same with a corner reflector. The panel or patch antennas lend themselves to mass production. They're usually nothing more than a plated circuit board inside. Once the dimensions are determined, they can be cranked out automagically, with little variations from unit to unit. I can't say the same for mechanical contrivances like a yagi.

Yagi's are also susceptible to icing, bird perching, and being used as a foot peg when climbing a tower. The traditional end mounting causes problems in routing the coax cable so that it does not detune the yagi.

Answer: A 15dBi yagi is about 18" long. For example:

The antenna gain increase 3dB for every doubling in the length of the yagi. So, doing it the hard way: Gain Length (dBi) (inches) 15 18 18 36 21 72 24 144 So, to equal the gain of a 24dBi 2.4GHz dish, you need a 12 ft long yagi. I don't think that would sell too well.

Thanks guys. Appreciate the education.

Back to topic.

Steve

Just for a rough idea, in our installation, I'm covering triple that distance with two panel antennas. One is an effective 10 (after cable loss) dbi and the other is 14 dbi.

The AP is a Buffalo HP and the client is a Linksys WRT54G. I'm getting about 40 db S/N reading in the firmware on the weaker (Linksys) end.

In other words, I've got more antenna than I need. You could get by with two 12 db antennas with just about any radio, I'd venture to guess.

Might even work with a stock omni on the AP and a 14-19 dbi panel on the client. Or vice versa.

If you really have a clear fresnel zone and all that.

But still, do the link calcs.

Steve