What is the maximum height of a wifi signal in atmosphere? I am not mentioning range and also I dont want answers in milliWatt. I want to know answer in kilometers or meters.

closed as unclear what you're asking by PeterJ, Andy aka, AndrejaKo, Majenko, Matt Young Jun 18 '14 at 12:13

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    if you are not mentioning range, then I am confused. what do you mean by "height"? vertical range? – nidhin Jun 18 '14 at 5:40
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    My guesstimate: The range would be the same as horizontally since the atmosphere does not change much during that range. One thing to consider is that those "omnidirectional" stick-like antennas don't have the same gain in every direction (think sphere), instead they have a slightly smaller gain along their axis (think donut shaped). – 0x6d64 Jun 18 '14 at 5:59
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    The maximum height is infinity because the signal gets smaller but still exists but falls below the noise threshold so maybe you need to consider this and rephrase your question to be more meaningful. – Andy aka Jun 18 '14 at 7:15
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    Just for the record, I down-voted and close-voted, but I did not do that due to the language used but because of the constraints of the question. It's obvious that OP doesn't know what's needed to ask the question properly, that he isn't interested in learning and that at the same time he isn't providing a good scenario where wizards who are aware of the first two things I mentioned can do their magic and provide an answer in requested units. – AndrejaKo Jun 18 '14 at 9:51
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    And frankly three detailed answers shows that the question is not unclear ffs. – Passerby Jun 18 '14 at 11:40
up vote 4 down vote accepted

It's difficult (almost impossible) to answer this question.

Why? Because the range (vertial or not) depends a lot on factors that you did not specify.

First you should have a look at notions such as "Link budget" Wikipedia

$$ P_{RX} = P_{TX} + G_{TX} - L_{TX} - L_{FS} - L_M + G_{RX} - L_{RX} \,$$

where:

\$P_{RX}\$ = received power (dBm)

\$P_{TX}\$ = transmitter output power (dBm)

\$G_{TX}\$ = transmitter antenna gain (dBi)

\$L_{TX}\$ = transmitter losses (coax, connectors...) (dB)

\$L_{FS}\$ = free space loss or path loss (dB)

\$L_M\$ = miscellaneous losses (fading margin, body loss, polarization mismatch, other losses...) (dB)

\$G_{RX}\$ = receiver antenna gain (dBi)

\$L_{RX}\$ = receiver losses (coax, connectors...) (dB)

You can see that the antenna gain is part of the equation. Using the stock "omni" antenna sold with the WiFi access point will not achieve the same distance that using a very directional antenna such as a Yagi Uda or a parabolic one. Without specifying this, it's impossible to give you a number for the range. Then it comes to the transmitter power and receiver sensitivity. Each access point and WiFi card is different.

But, there is also another factor not related to the strength of the signal: the time delay.

The WiFi protocol (which one? this has to be defined) defines the maximum delay between a sent packet and the related acknowledge. If the distance is too big, a timeout will occur and this will not work. But without knowing the specific WiFi norm you plan to use, it's impossible to give you a number.

According to Wikipedia page about long range WiFi using modified firmware in order to increase the timeout value and dedicated antennas, ranges up to 304 km is possible without using additional amplifiers.

It varies by Wifi version, and speed/data rates:

The concept of range for wireless LANs is pretty basic. Range is usually thought of as a measure of distance -- the distance between two wireless stations at which they can effectively communicate. For typical Wi-Fi systems, range is the distance between a laptop client and the access point (AP) it is using.

Any discussion of wireless range also has to include data rate (not to be confused with the actual, physical throughput). In wireless systems, you can trade off data rate for range – at lower data rates, it is possible to communicate at greater distances. The 802.11 standard supports multiple data rates at the physical layer. 802.11 has an automatic rate fallback mechanism that reduces the data rate when communication degrades in order to maintain a better link between a wireless client and AP.

And by antenna type:

enter image description here enter image description here enter image description here

And as you can see in the picture above, a standard wifi antenna like you normally get, has a donut/torus shaped radiation pattern. That means if the antenna is vertical/straight up and down/perpendicular to the ground/90° to the floor, it has basically 0 radiation at a 90° angle while weaker at other angles. If you make the antenna parallel to the ground/lay it flat, it will have better vertical (compared to us) performance.

And the farther away the two nodes are (The Wifi router/access point, and the computer/laptop), the slower the wifi speed is. 802.11n improves on 802.11b/g by using a second antenna, spaced a half wavelength away. 802.11n is shown to be 250m effective range, outdoors, with no obstructions but the data rate and type of antenna used is unknown. And that's before interference. The more wifi traffic on the same channel, the slower and weaker the effective signal will be.

In the end it depends on A, the antenna used, B, the radio power, C, obstructions, D, the direction of the antenna, E, interference from other sources on the same radio bandwidth/channel, F, Speed required, so there is no single answer.

I don't know what you mean by "I am not mentioning range." AFAIK that is the only way to answer this question.

The range of Wi-Fi depends on the protocol. The range of 802.11n is about twice that of 802.11b and g.

The typical outdoor range for 802.11n is approximately 820 feet. Although this is assumed to be horizontal, it should apply to a vertical distance also.

Although not explicitly stated, I am going to assume this figure of 820 feet assumes the the use of an omnidirectional dipole antenna, since it is the most common type (i.e. the "rubber duck" antenna that comes with routers).

However by using a high-gain directional antenna, ranges of several kilometers can be achieved. The examples given are all point to point horizontally, but it again should apply vertically also.

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    Are you sure will horizontal and vertical range be same? – rajasekar25 Jun 18 '14 at 7:31
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    @rajasekar25 As long as the antenna is oriented correctly, to account for the vertical vs horizontal direction, going "up" rather than "sideways" should make no difference. – tcrosley Jun 18 '14 at 9:32

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