Wireless AP's query?

I know this is an odd request, and I don't know if i'm in the correct group, but i'm trying to plan out a wireless network - can anyone answer the following question?

Indoors, in an open space 802.11g what range to you think you'd get on a roof mounted AP?

20 metres?

Am I making sense?

Found this to be a tough one, no manufacturer seems to want to pin down a specific range for their APs?

Regards, James

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Jellis hath wroth:

Yes, just about anyone can answer your question.

See the FAQ at:

Intel's numbers for range are somewhat optimistic.

Maybe. The problem is that there are tradeoffs. I'll try to outline the basics. You get to Google for details.

  1. Antennas make a huge difference in range. Bigger is NOT necessarily better as the antenna pattern gets narrower with increasing gain.
  2. For gain, 6dB = 2 times the range 12dB = 4 times the range 24dB = 16 times the range
  3. Coaxial cable is VERY lossy at 2.4GHz. Make an effort to keep the coax cable runs to a minimum. Better yet, with a rooftop mount, put the wireless access point in a weather proof box at the antenna and run PoE.
  4. Range and speed are inversely related. For everything else being equal, if you go 4 times as far away, you're speed gets cut in half. Actually, it's worse than that as you'll probably pickup reflections, which will reduce the speed even more.
  5. Reflections are a problem. The ability to handle reflections gracefully is why MIMO is superior to 802.11g, which is in turn, superior to 802.11b.
  6. All data sheets lie. Cut all promises at least in half or more.

Before anyone can answer your question with a specific number, you need to supply specific numbers to work with. Range can be calculated but we need to know what you have to work with (topography, line of sight, altitudes, etc) and what hardware you were considering.

You also need to untangle your question as to whether you really want to talk to an indoor client from an outdoor antenna. If that's your question, then some clue as to the composition of all the building material in the way in needed. Also, be advised that the absolute worst location for communicating to a rooftop antenna is directly below the antenna. There's almost no RF sent in that direction.

Barely. Not enough to answer or decode your question, but enough to bury you in buzzwords so you can do some effective searching and reading.

That's like the gas mileage specification for cars. Your Km's will vary. It really depends on a large number of parameters, some of which you have no control over (interference, reflections). If you want a number, you have to supply numbers with which to do the calcs.

I suggest you download and skim:

It's Intel's Wireless Hotspot Deployment Guide, which has evaporated from their web pile. There's quite a bit in there on range, coverage, gains, specs, and how things work. Well worth reading.

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Jeff Liebermann

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