Maximum WiFi Range

I am studying with FutureLearn, and on the course "Cyber Security", the question of WiFi maximum range has come up.

One of the other participants has posted this comment-
"
Not sure your are right in saying wifi has a very limited range. I have picked up a wifi signal and logged on to it from a distance of two miles. Admittedly I had an aerial but so could any hacker!
"

Apart from possible confusion such as BT FON multiple Hotspots, have any of you any experience of such long distances?

With appropriate antenna yes this is possible presuming you have a clear line of sight and the output from the Wi-Fi source is sufficiently directional too.

Take a look at the various Wi-Fi kit for long distance links sold by www.solwise.co.uk

Also it helps when you have a directional antenna as well, just means that you turn the beam until you get a strong signal.

Paul

Thanks to both of you.

http://www.solwise.co.uk/downloads/files/linking-bui...

Section 1.3 with its table is interesting.

Although I find 5a and 5b apparently contradicting the norm.

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I am trying to get more information from the other course student.

In the meantime, I would appreciate comments from anyone with practical experience of such longer distances for Wi Fi, whether intentional, ie with equipment intended for such ranges; or "unintended".

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It can be amazing what happens with radio waves.

Many years back, I was listening to two radio amateurs, one "just down the road" in Edinburgh, the other in New Zealand.

My aerial was the proverbial "short piece of string" to a clothes pole in the back garden, hemmed in all round by buildings.

I don't know the NZ amateur's rig; but the Edinburgh amateur was a Cemetery Superintendent and his various aerials effectively were well clear of any buildings etc, with a public park across the road.

I had no troubles picking up both; but the Edinburgh amateur was having great difficulty receiving the signals from NZ.

In reply to a post by eckiedoo:

Thanks to both of you.

It can be amazing what happens with radio waves.

Many years back, I was listening to two radio amateurs, one "just down the road" in Edinburgh, the other in New Zealand.

My aerial was the proverbial "short piece of string" to a clothes pole in the back garden, hemmed in all round by buildings.

I don't know the NZ amateur's rig; but the Edinburgh amateur was a Cemetery Superintendent and his various aerials effectively were well clear of any buildings etc, with a public park across the road.

I had no troubles picking up both; but the Edinburgh amateur was having great difficulty receiving the signals from NZ.

Yeah, I just love listening and talking to them, I have a tri-band (5m, 2m and 70cm) vertical antenna on the roof along with a long wire (doublet HF) antenna across my garden, now the home made wire antenna can contact people all around the world on anything from 10W to 50W by bouncing the signal, however people down the road cannot or have issues hearing me

Paul

Directional antennas concentrate the beam so have a higher field strength at the transmitter and thus higher all along the path when compared to a a basic Omni. A directional received will again concentrate the received signal and effectively amplify it.

Two miles could be achieved with a clear line of site and good antenna ... I believe some experiments have actually achieved even more.

I have done quite a lot of work in the 1.6 - 1.8 GHz band and that is good for 40,000km (25,000 miles) with around 10 watts. So, 2 miles at 100mW should not be an issue - with the right equipment.

At 25,000 miles the curvature of the earth must have a pretty big impact? Is this off high masts (presumably 4Kms high each to get line of sight) or using some form of orthogonal frequency division multiplexing or air to air/surface to air?

Have experience of getting an installation to connect 2 buildings over a small hill at about 10 miles distance where they used orthogonal frequency division multiplexing to improve signal strength.

Of course lower frequencies can give better distance/ability to get through obstacles.

Edited by ian72 (Tue 17-Feb-15 14:19:50)

In reply to a post by ian72:

At 25,000 miles the curvature of the earth must have a pretty big impact? Is this off high masts (presumably 4Kms high each to get line of site) or using some form of orthogonal frequency division multiplexing or air to air/surface to air?

It could likely be very high i.e. surface to (near) vacuum.

In reply to a post by jelv:

In reply to a post by ian72:

At 25,000 miles the curvature of the earth must have a pretty big impact? Is this off high masts (presumably 4Kms high each to get line of site) or using some form of orthogonal frequency division multiplexing or air to air/surface to air?

It could likely be very high i.e. surface to (near) vacuum.

Think you could be on to the right thing. Looks like geosynchronous orbit so presumably satellite comms. Makes for an easier line of sight capability if the satellite is always directly (ish) over your head.

Correct ...


GeoSync is 35,786 km above the equator and if te transmitter is at around 75 deg N or S and offset by 50 deg of longitude it will tend towards 40,000 km.

I spent time in the Arctic working and testing the transmitters where the elevation to the satellite at a couple of metres above ground or sea level was getting close to 0 degrees.

Sounds like interesting work, although a little chilly...

In reply to a post by ian72:

Sounds like interesting work, although a little chilly...

I was 'kin cold, hitting -40 at times and it was during January and February! So we saw very little daylight.

2.4 ghz wifi can go a long way with the right aerials, a team some years back managed over 100 km ..

On the 5 Ghz band you can go even further as the noise floor is lower and aerial sizes per gain more manageable.

We rely on such links that run 30km+ every day here

the biggest issue is the ack timing. domestic wifi kit has a fixed distance limit, the acknowledge timeout.

this is how long after one end sends a transmission it will wait to expect a reply. this time increases with distance (speed of light) . if the timeout is fixed to short range then longer distances will cause the system to keep tripping over itself and re-sending data.

dynamic ack timing means the system works out the link distance thereby allowing more time for a reply.

In reply to a post by eckiedoo:

I am studying with FutureLearn, and on the course "Cyber Security", the question of WiFi maximum range has come up.

One of the other participants has posted this comment-
"
Not sure your are right in saying wifi has a very limited range. I have picked up a wifi signal and logged on to it from a distance of two miles. Admittedly I had an aerial but so could any hacker!
"

Apart from possible confusion such as BT FON multiple Hotspots, have any of you any experience of such long distances?

Thanks very much Bill and others

Interesting what such an apparently simple question brings to light.

I have experience of 10 GHz, with 154 and 105 Dipoles, respectively Azimuth and Elevation, fed from variable-width waveguide, for Ground Controlled Approach (talk-Down), MPN1A, back in the late 1950s.

The beam widths were 2 Degrees by 0.5 Degree, achieved by the large number of dipoles, swinging over arcs of 10 Degrees from the variation of (guide) wavelength within the variable-width waveguide, so changing the phasing of the drive to the dipoles.

Normal working range was 10 miles, to cover the Final Approach, there being a separate 3 GHz Search system out to 30 miles, to talk the pilots round in to the Precision beams above.

With a lot of careful tuning, cleaning of the rigid waveguide feeds etc, I did get the 10 GHz Precision system working out to 30 miles. The variable-width waveguide was too complex to play with.

Arthur C Clarke, the later Science Fiction writer, was involved in its development and being put in to service during WW2.

His 1964 book, "Glide Path", describes his experiences.

In reply to a post by MrSaffron:

With appropriate antenna yes this is possible presuming you have a clear line of sight and the output from the Wi-Fi source is sufficiently directional too.

Take a look at the various Wi-Fi kit for long distance links sold by www.solwise.co.uk

Also there used to be quite a few DIY designs for waveguide aerials using food cans etc on the internet .
I suspect the main problem with highly directional aerials at both ends is actually getting them even roughly aligned .

In reply to a post by rarrar:

In reply to a post by MrSaffron:

With appropriate antenna yes this is possible presuming you have a clear line of sight and the output from the Wi-Fi source is sufficiently directional too.

Take a look at the various Wi-Fi kit for long distance links sold by www.solwise.co.uk

Also there used to be quite a few DIY designs for waveguide aerials using food cans etc on the internet .
I suspect the main problem with highly directional aerials at both ends is actually getting them even roughly aligned .

I've seen it working with a Pringles Tube cut down.

When I looked after the local charity run schools computer network for free I set up a WiFi link using two Satellite dishes with a WiFi dongal at the focal point, one at the school high up on a chimney and another on the end of our house high up in line with the school over 1kilometer away.
From that I could remotely run the Network

This is a good site for idea's http://www.wlan.org.uk/antenna-page.html

Thanks Aptman, some interesting aspects coming to light!

To be honest though, I had raised the question thinking in the unstated terms of ordinary "domestic" WiFi, and wandering around in the proximity of one's home.

Another useful cheap way of boosting WiFi around the home etc. is to use some old WiFi modems/routers (I get mine free off freecycle ) and set them up as 'Access Points' (get details off the web to do that !).
I have a very large house and garden and good WiFi is available all over.

Thanks, Aptman.

I have done that experimentally; but normally would not need to do so.

I also have Connectify on my various portable PCs, so if necessary could also readily extend that way - but normally it is switched off.

In reply to a post by APTMAN:

When I looked after the local charity run schools computer network for free I set up a WiFi link using two Satellite dishes with a WiFi dongal at the focal point, one at the school high up on a chimney and another on the end of our house high up in line with the school over 1kilometer away.

This approach has to be done with care. You may be exceeding the power limits for unlicensed use (which are specified in a way that takes antenna gain into account), also you may be radiating excessive energy outside the band (as the gain will also apply to unwanted out of band radiation).

Many of the 2.4GHz projects are from amateurs, who can legally run higher powers on this band using their amateur licences. UK amateurs have access to 2400-2450MHz (equating to channels 1-6) with a power limit of 50W PEP for Intermediate licences and 400W PEP for Full licences. Foundation licences do not include this band. Of course, using an amateur licence to run higher powers puts the operation under amateur terms and conditions with respect to station identification and content of messages (which would prohibit communication other than with another licensed amateur).

There are possible safety implications of running directional antennas because of the on-axis field strength.


I'm not saying there was anything wrong with your installation. I just wanted to remind people that merely getting a radio based system working is not enough - you have to satisfy yourself that the installation is safe and legal.