Hi, I made two units for a friend to be used to bridge a network over 50mtrs.
Both CPE's in low 5Ghz band, 40Mhz wide channel.
Both units where fit behind double glazed windows and both had to look under a 50 degree towards each other.
Both power settings in default.
Both units where impossible to establish a connection with each other although the signal reading showed high signals.
When one unit had the window opened in front of it the connection immediately was established with good strength, good rates and good CCQ and 25Mb internet traffic was not problem.
Close the window again and association was lost.....

These so called "Thermopane" windows are double glazed with some gas fill and maybe even some coating.
So, can it be that due the angle the signals have to pass the glass, the reflection is such the antenna's won't receive each others signal properly any more?
Of because it is just too much. I mean, one window open but the other side still closed is not a problem?
Or could it be the coating?
Or the gas?


Has anybody experienced the same and has anybody any idea what could be the issue?
Normally the used frequency band should not have such a problem passing through glass isn't it?

I used nanostations for this purpose, but since this is more just wireless technology related imho I ask the question on this forum.

Hi,

With us, this problem was actually the angle of the antennas with the double glazed glass. We checked on the gas and since this is 'inert' it should not be the problem. We swapped the antennas for directional grids and managed to get the link up but we had to use full power on both sides (5Ghz band) and the client decided to not use the link since to him it was 'dangerous'.

Our angle was sideways not up/down but I'm still convinced it was the double glass.

Rgds,
Mark

ive seen the same thing even thru a single pane large window - it had some weird type of coating on it that caused 5ghz to not pass thru very well at all. Maybe its a metallic window tint or something.

People were using Pringles cans (cardboard for those that don't know) as antennas. For my wireless mouse I was using the sheetrock wall as a reflector.

I don't know if it is something in the glass or not, but it has to create some reflections and the sharper the angle the worse it would be I imagine.

I don't find this surprising at all. Anything that you put between two RF transceivers is going to interfere with and attenuate the signal to some extent. That depends on the material, it's density, and the the length of transit. It may also refract the signal (think light through a prism) and the lower the angle the stronger that effect will be.

With 5Ghz you're in the microwave realm at a wavelength of 6cm, and half wave of 3cm. If you look at the cross section through that kind of double glazed window at 50 degrees you're very close to that half wave (think internal reflections and self interference). Add the fact that low emissivity glass like Thermopane windows is designed to block IR (the next thing up the EM frequency charts), has multiple refracting/reflecting surfaces, and generally have some kind of metallic (Silver is common) or metallic oxide (SnO2 is common) coating and it's one of those "oh yeah..." moments. See: http://en.wikipedia.org/wiki/Low_emissivity

I remember working with an antenna specialist who was trying to get signals for a demo/proof-of-concept avionics package through an airplane window (which are mostly multi layer acrylic and less dense than glass) and having a truly miserable time of it.

Depending on the building materials you may actually have better luck shooting through a wall, especially if you can get the angle of incidence closer to 90 degrees. Since the window opens you may also be able mount the antenna outside, and squeeze a cable through the weatherstripping around the windows.

I don't find this surprising at all. Anything that you put between two RF transceivers is going to interfere with and attenuate the signal to some extent. That depends on the material, it's density, and the the length of transit. It may also refract the signal (think light through a prism) and the lower the angle the stronger that effect will be.

With 5Ghz you're in the microwave realm at a wavelength of 6cm, and half wave of 3cm. If you look at the cross section through that kind of double glazed window at 50 degrees you're very close to that half wave (think internal reflections and self interference). Add the fact that low emissivity glass like Thermopane windows is designed to block IR (the next thing up the EM frequency charts), has multiple refracting/reflecting surfaces, and generally have some kind of metallic (Silver is common) or metallic oxide (SnO2 is common) coating and it's one of those "oh yeah..." moments. See: http://en.wikipedia.org/wiki/Low_emissivity

After some ´googling´ and going back to my school years both of the mentioned can indeed be the reason.
In fact I think a ´metallic´ coat together with the needed angle made it almost like a block for the 3cm waves.

Anyway, its been interesting reading both here and via google. You think you know all but then we find ourself in a whole new field of ´knowledge´...

I've seen something similar during a pentest. We entered the network through their wireless points so one of their reactions was to install this wifi blocking film on all the windows. I of course took a peak at the rolls to what this special stuff was. It was ordinary metallic window film which I'm sure they were charging at least twice or more as much as it would usually go for. Instead of actually putting some effort into securing their wireless they tried to block it getting out... /facepalm

We pointed it out during the followup review that it may have blocked a little at the windows, but there were still the walls. It didn't come close to providing any security. They finally took our advise and got a consultant in. We did get the comment that they'd wished they'd hired the consultant before spending the money on the 'magic' film. I got the impression it was rather expensive.