Is it normal to lose 15 dB @ 2.4Ghz through double-pane window glass?

Q: Is it normal to lose 15 decibels through a double-pane window?

The storm blew down my 2.4Ghz WISP WiFi antenna ...

So a friend stopped by to lend me his Ubiquiti AirGrid M2 Hi-Power (Tx

28dBm, Rx -97dBm) radio & 17x24-inch 20dBi antenna combination.

He's only about a mile away so he opened up his Internet service to me to mooch off of until I could get my WISP antenna back in working order.

The problem

Reply to
Martin C.
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Here is the picture of my temporary 2.4Ghz setup:

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OUTSIDE: I get -77 dB received signal on AirOS. INSIDE: I get -92 dB received signal on AirOS.

The difference is that it won't work inside; but it works fine outside (just a foot or two away) on the deck outside the window.

It's not the screen (as it's cloth and we tested that). It's the window (which we tested by opening it up).

Since it's cold and windy on the deck, we would like to use the antenna inside. First we have to figure out WHY we lose 15 dB through a simple window!

Can someone tell me why?

Reply to
Martin C.

People more knowledgeable than me will be along shortly, I presume, but my guess is that the window glass has an energy efficient coating that blocks much of the signal.

It wouldn't surprise me if you did a lot better by moving the antenna to either side of the window. That may give you significantly more signal to work with.

Reply to
Char Jackson

Is the glass coated with a titanium nitride or titanium dioxide, Low-E IR reflective coating? It's blocks RF quite nicely at about 45 ohms per square resistivity.

Not a great data sheet on the topic, but it does offer some clues:

More, when I'm awake.

Reply to
Jeff Liebermann

Hi Jeff,

I have no idea what the window is made of, but you gave me a hint so I did find this document which says a typical coated (doesn't say which coating) double-pane window will attenuate by 13 decibels whereas a 'normal' exterior window will only attenuate 7 Db.

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Reply to
Martin C.

Hi Jeff,

I'm in the Santa Cruz mountains, with more sun than I know what to do with, so it would make sense the previous owner used a special coated glass.

Looking up more details, I found this "Residential Glass Technical Guide":

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But I can't tell what coating they used.

Reply to
Martin C.

Site seems to be down at this time. Low-E has been required for new construction in California since about 2002. From your photo, the window construction looks very recent and will likely use Low-E glass.

The numbers for attenuation through various materials vary wildly depending on testing methodology. For example, if your test radio is fairly close to the window, you will get some value. However, if the window is not much larger than the antenna, and you back off some distance from the window, it starts to look like an aperature, complete with edge diffraction and Fresnel zone effects. Size matters as does angle of incidence. In your photo at:

The dish is much too close to the window frame at the top.

Table of attenuations (unfortunately missing Low-E glass.

In the not so distant past, I installed a wireless access point at a car wash. The router and antenna were inside, while the customers were mostly outside. In between was a rather large plate glass picture window. To 2.4/5.7GHz, it was almost like a shielded wall. I never bothered to measure the loss, but it was sufficiently high to require installing a 2nd outside wireless access point to give the customers some coverage.

Meanwhile, the local university installed Low-E glass in several new buildings, only to find that its micro-cellular rooftop system didn't work inside the buildings. Indoor radios had to be added in some buildings.

There are various creative ways to identify Low-E glass:

I use an IR thermometer and anything hot, such as a cigarette igniter. If the heat from the lighter goes through the glass, it's not Low-E. If it blocks IR, it's Low-E. If you can't get to both sides of the glass, check if it reflects IR.

Reply to
Jeff Liebermann

I'm in the trees in Ben Lomond. Send me some of that sun as the deep dark forest gets to me every winter.

It's not so special. Low-E is has been required for new construction and permitted remodels for at least 10 years in SCZ county.

Most Low-E materials will block RF. The only one that is specifically designed to NOT block RF are the nano-ceramic coated variety. Those are rare, expensive, and optically inferior to the more common sputtered aluminum or sliver, tin dioxide, titanium nitride, and titanium dioxide flavors.

Are you using Hilltop Internet or SurfnetC? In both cases, methinks you should install the dish on the roof, mount the radio behind the dish to reduce coax cable RF losses, use PoE to run the radio, and do plenty of waterproofing. There was a long thread in this newsgroup on the subject of getting wireless service in the SCZ mountains from Hilltop in this newsgroup recently.

Reply to
Jeff Liebermann

Or glass with a high metal content (e.g leaded glass). Typical glass is silicon dioxide (and silicon is a metal).

A plastic window would be better. Plastics are hydrocarbons; no metals.

Reply to
D. Stussy

There are only these WISP providers in the Santa Cruz Mountains that I know of which serve my area: HilltopInternet.com Surfnetc.com Ridgewireless.com Ethericnetworks.com SuperSpeedy.net

For satellite, there are only two: Viasat Exede Hughesnet.com

Reply to
Martin C.

It is a matter of fulfilling Ca Title 24. If you don't use low-E glass, you have to make up the loss elsewhere.

It seems to me the RF shielding of low-e glass is a good thing, given how the government likes to spy on citizens in the post 9/11 world. ;-) Also, for us city dwellers, we need all the shielding we can get from nearby wifi.

Off topic, but I'm about to take a hammer to this f-ing Linksys router. The wifi portion is locking up. I have to reboot the f-er. I suppose it can live as an expensive switch.

Reply to
miso

Before you lose all hope, ye who enter there... see if you've got another wall wart with a similar rating. Often these lockups are due to power supply issues.

(Far from always, of course, but it's easy enough to check out).

Reply to
danny burstein

Unfortunately it is a 12V regulated switcher. I will have to either bench it or buy another wall wart. [Actually soap on a rope.] The coaxial connector isn't standard. [I've often wondered what is the reason behind so many different two pin power connectors.]

Note that the wired portion works just fine. I suspect if I open it upm the wifi is an OEM board. That would explain one function being flaky while the rest of the box works.

I'll haul the wall wart with me on the next trip to the surplus shop and see if I can get a match.

Reply to
miso

After I installed Low E windows in my house I could no longer use my laptop out on the patio. Bummer that was my favorite Sunday morning retreat.

Jimmie

Reply to
JIMMIE

on the patio. Bummer that was my favorite Sunday morning retreat.

It should be pretty simple to add an access point to service that area.

Reply to
Char Jackson

When the weather warms up, open the window, unless yo got aluminum screen.

Greg

Reply to
gregz

Screen is cloth. The antenna that was damaged in the storm is fixed. I learned a lot. Coated glass can block RF dead!

It's all good now!

Thanks to everyone!

Reply to
Martin C.

A black screen cloth could have attenuation.

Greg

Reply to
gregz

Do you think they use carbon?

Reply to
miso

Some paints do, and stuff to be uv resistant.

Greg

Reply to
gregz

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