WiFi transmit and receive range

Google "Friis equation." It's actually just a bit of algebraic manipulation starting with the idea that power radiating into free space must fall off (in density, W/m^2) with the square of distance... in free space. In The Real World, you can demonstrate that there are worst case scenarions where power falls off with the _cube_ of distance (ouch!); people doing link calculations pick there favorite power, with 2.5 not being uncommon.

The way to think of free space attenuation is that each oscillation or wavelength of a signal gets attenuated by a certain, constant amounts. Hence, if you double the frequency, you halve the wavelength and double the attenuation over a given distancedoubles as well.

---Joel Kolstad

That's NOT what happens! The equation assumes a receiving antenna with a fixed size in wavelengths. Higher frequency means a smaller antenna that intercepts less energy. _That_ is why the equation gives higher path loss for higher frequencies. Path loss is a misnomer, in fact.

Jeroen Belleman

Please help me to calculate. The frequency for 802.11b is 2.4GHz, and 802.11g is 5.2GHz, The maximum FCC allow unlicensed power is 0.5watts = 500mWatts. So what is the range in distance? Thank you.

This is impossible to calculate without knowing the gain of your antennas (and if you're indoors or outdoors). For point-to-point links, with 500mW you can go tens of miles... for a roughly omnidirectional antenna, you most likely won't even get one mile.

A bunch of nerds went over 70 miles in the desert in Nevada, I copied the article and gave it to the company wireless guy's as I can't connect to the access point 20' away! At home my signal is good in the house and two houses on both sides of me........

I like these guy's approach:

OK, for both external indoor and outdoor operating in urban and rural spaces, using typical 2.4GHz 24 dB Gain grid antenna, how do I calculate the range?

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"Calculate" range ????

You may be able to "Calculate" signal strength in an ideal environmet.

But Range ???

If you can model every foot of ground and air space between the transmitter and receiver, well maybe not.

Good Luck

Donald

Does the transmitter put out the full 500 mw? How many Microvolts are required at the receiver's antenna to get an acceptable error rate? Is there anything along the path that can cause multi-path reception? How well made are the antennas? Is there any chance the receiver will be desensed from another source? How accurately are the antennas aimed? You don't give anywhere near enough data to give a valid answer.

Guys- propagation of 2.4GHz WiFi is so influenced by diverse reflections & obstructions that it's near impossible to factor exact range into calculations. Additionally local spectrum noise ( from microwave ovens, cordless phones, APs, BlueTooth etc ) can mask weak signals. Weather & even season can be a factor too- very dry air in winter can sustain longer links that moist summer air. Hence it's STRONGLY suggested that you grab a WiFi laptop or PDA & run NetStumbler or WiFiFoFum( WFFF) while doing a site audit, perhaps with one of our cookware parabolas. This is usually THE very first thing to do - see a ~1km LOS ( line of sight) proof of concept trial we ran in Wellington NZ =>

There's just something cool about the term "chinese parabolic cookware." :)

Similiar situation, how does cellular telephone operator estimate cover a city or an area? So since WiFi is higher in frequency, how do they estimate how to cover an area?

Its right there in the name: Cell, or small areas covered by a single base station that are connected to provide wider coverage.

This kind of question belongs in news:sci.electronics.basics

Computer models for the rough geography, guru experience for the rest. Then measurements and adjustments to antenna patterns and power as needed.

The situation is slightly different in that they are not looking for maximum range for a given setup, but adjust the setup to get the needed range.

Kind regards,

Iwo

an

You look at the place, make an educated guess about the absorption and reflection properties of the landscape, buildings and other stuff and go by gut feeling.

It's about as accurate as forecasting the weather. In theory, it can be calculated exactly, but in reality you never have sufficient information to do it.

It's not an exact science. In free space, you can calculate exactly, after that people tend to use rules of thumb.

Kind regards,

Iwo

Yeah, although for big cities it seems that, e.g., the cell phone guys are willing to pay for some pretty fancy software to try to get their estimates correct. See:

Have you seen the computers the weather guys are using? ;-)

Iwo

So, rough design estimest, would you say every 1 square mile per antenna point, or 2 or 3 or 5 square mile?

I know, nobody want Cell or WiFi antenna tower in front of their house.