# How many walls can wifi transmit through?

• posted

This seems like a newbie question. But here goes...

I want to link two computers together with wifi, preferably g-type. Both computers are within the same house, but are ~8 meters apart, and separated by three interior walls.

I have no idea how much those interior walls will weaken the signal. Can anyone tell me how well this will work please, if at all?

Thanks

• posted

they do not link direct but go through the router so where is it.

• posted

The router will be right adjacent to one of the computers...

• posted

It's hard to say without knowing what your walls are made of.

• posted

It depends on what's inside the walls. If the 3 walls are just clapboard, cardboard, vegetable board, or Japanese wall panels, you could easily go through a dozen walls. However, if you have aluminum foil backed insulation in the walls, even one wall would be a challenge.

From the FAQ, attenuation of various building materials:

There are several ways to use the chart. Basically, 6dB loss equals half your range. 12dB loss is 1/4th the range.

Put your router in a window and go for a walk with your wireless connected computah. The idea is to get a rough idea of how far you can go before the signal ceases being usable. Ping with large packets works well for this test. With the stock antennas, about 100 meters is typical.

If you're able to go 100 meters, and still get a RELIABLE connection, then at 8 meters, you can tolerate a: 10 log (100/8) = 11dB loss Looking at the chart, one interior solid wall is about 9dB loss, which means you can go through one solid wall, but not two (which would be

18dB loss).

Performance can be enhanced by changing antennas. Using the above example, a fairly crude direction antenna, with 8dBi gain, will give you 6dB more to work with. (That's because the antenna gain of your existing rubber ducky router antenna is about 2dBi). In theory, you should then be able to tolerate 11+6=17dB loss, or almost enough to make it through two 9dB loss inside walls.

Of course, things never get better, only worse. When dealing with inside walls, multipath and reflections can become a problem. Just moving a few cm may be the difference between decent thruput and no signal. It may work, but isn't particularly reliable.

My usual advice is once you get beyond one wall, find an alternative such as running the CAT5 cable, power line networking, or phone line networking.

• posted

A lurker says thank you.

Lou

• posted

Hmmm so I can pull out my NOS power line networking system and use that? I was going to dispose of it since I have wireless routers on my DSL system.

I have run a Cat-5 cable from one side of my house through the attic to the other side. Then I could have hooked up a wireless router there too, but it went straight to one computer instead.

-- Thanks from another lurker! ;-) later, (One out of many daves)

• posted

Yep. That's what wi-fi is for. The problem is that it's not as reliable as wired networking. If you have a choice, CAT5 is always better.

You can have it both ways. Install a 2nd wireless access point at the computer end:

Put it on a different channel (1,6 or 11) as the main router and disable the DHCP server. If your computer is a laptop with wireless, you now have connectivity.

What do you mean by "I have wireless routers"? You have more than one in the system?

• posted

In my case, the three walls are hollow (6-9db), so overall my situation is marginal. But I will find another way.

• posted

Yes I have two wireless routers, one that is the DSL modem combo and a DLink wireless router that has a better range.

I did "Put it on a different channel (1,6 or 11) as the main router and disable the DHCP server"

If I redo another place, I will plan out the CAT-5 cabling inside of the walls!

thanks!

• posted

If the walls are just that.....hollow.....then why marginal ?

My wireless rtr is in my basement, at one end of the house, inside a metal cabinet mounted on the wall (circa 1955). This is my comm cabinet with a rack mount switch and patch panel and (8) CAT5 runs come back to this box. The cable modem is here as well. The wireless rtr is a small D- Link with a cheesy little 3" swivel up antenna. I leave the cabinet door open, and have complete wireless coverage anywhere in the entire house. (It's a ranch so only one floor.)

A 'prediction' of 'marginal' is just that, a prediction. Even the most expensive engineering tools are only making 'predictions'. You can never be sure about anything wireless until you actually try it.

(Well that's not completely true........but.)

• posted

Hollow? What are the walls made of? Gypsum board, vegetable board, plywood, concrete, etc? Fiberglass insulation has almost no effect on

2.4GHz losses, but the usual aluminum foil backing is fatal. My guess is hollow wall drywall is good for about -4dB loss, which makes it worth trying.

Y'er welcome.

Hint: You'll get better answers if you supply specifics, numbers, equipment list, materials, conditions, etc.

• posted

capww8 had written this in response to

: inconoclastical,

You shouldn't really have any trouble, unless the walls are steel reinforced concrete, with a microwave in the middle. If it doesn't work, look at the locations of your 2.4 ghz spectrum wireless telephones... they will wreak havok on a small wlan.

Another good solution may be the use of a powerline LAN adapter. It will be comparably priced, but less flexible. The up-side is that you'll likely get better through-put than you would on the WLAN.

------------------------------------- ic> This seems like a newbie question. But here goes...

• posted

Yes, I guess I was vague.

I live in one of three connected flats. I'm in the flat at one end, and want to network with the guy in the flat at the other end, so that we can share a broadband connection. \$100 a month around here.But between us lies the vacant flat in the middle.

These flats were built as community housing in the late 50s, and having spent some winters here, I can attest that there is no insulation in those walls. And while the exterior walls are brick, the internal walls between the flats appear hollow, materials and thickness unknown.

Now, when I said earlier that there were 3 walls to penetrate, I wasn't quite honest. There are the two obvious walls that separate the flats. But I also counted a partition-closet (~50cm thick) in the adjacent flat as a third wall.

But eventually someone will move into the flat adjacent to me. So depending on what my new neighbour puts in his closet, it is hard to judge what attenuation that will cause. If he decides to hide some scrap metal in his closet, I'm screwed.

I liked you thorough treatment and maths above though, and if I had routers and/or wireless laptops lying around, I would just put it all together and see what signal I get. But really these are things I will have to purchase.

It is marginal, but I'm not a quitter. I'm thinking about climbing up the manhole in the ceiling, and seeing if I can get ethernet cable between our two flats. That would be cheaper in lots of ways.

But failing that, then I think I can position the WAP and wireless router creatively, such that it avoids that accursed partition-closet. And if the signal through the two hollow walls still isn't strong enough, then I can upgrade one or both the antennas to boost the signal.

So nothings a problem, just a matter of finding the best and cheapest way to do this I think... That said, I'm glad I asked the question, as everyone here has been most helpful with their answers :-)

Grant

• posted

Yes, I guess I was vague.

I live in one of three connected flats. I'm in the flat at one end, and want to network with the guy in the flat at the other end, so that we can share a broadband connection. \$100 a month around here.But between us lies the vacant flat in the middle.

These flats were built as community housing in the late 50s, and having spent some winters here, I can attest that there is no insulation in those walls. And while the exterior walls are brick, the internal walls between the flats appear hollow, materials and thickness unknown.

Now, when I said earlier that there were 3 walls to penetrate, I wasn't quite honest. There are the two obvious walls that separate the flats. But I also counted a partition-closet (~50cm thick) in the adjacent flat as a third wall.

But eventually someone will move into the flat adjacent to me. So depending on what my new neighbour puts in his closet, it is hard to judge what attenuation that will cause. If he decides to hide some scrap metal in his closet, I'm screwed.

I liked you thorough treatment and maths above though, and if I had routers and/or wireless laptops lying around, I would just put it all together and see what signal I get. But really these are things I will have to purchase.

It is marginal, but I'm not a quitter. I'm thinking about climbing up the manhole in the ceiling, and seeing if I can get ethernet cable between our two flats. That would be cheaper in lots of ways.

But failing that, then I think I can position the WAP and wireless router creatively, such that it avoids that accursed partition-closet. And if the signal through the two hollow walls still isn't strong enough, then I can upgrade one or both the antennas to boost the signal.

So nothings a problem, just a matter of finding the best and cheapest way to do this I think... That said, I'm glad I asked the question, as everyone here has been most helpful with their answers :-)

Grant

any chance of a common attic or basement (to run a cat5 cable thru), forced air heat/common heating ducts? shared coax for tv? (they have both powerline and coax networking)

• posted

...

I reckon you've already found it. That's the first thing I'd try if I didn't have any wireless kit to experiment with.

• posted

On Tue, 9 Jun 2009 17:25:44 -0700 (PDT), iconoclastical wrote in :

You can't at least borrow two wireless laptops? Most all laptops comes with Wi-Fi these days, and that's all you need to do a site survey.

Maybe, but it can cost more than you might think to run proper Ethernet wiring -- you've got a fairly long run, and you'll want to use proper (plenum rated) cable, attached properly, with permanent outlets at each end. In addition, you lose flexibility versus wireless -- I like being able to easily move around rather than being tied to an outlet.

That's probably a good idea, and can be done easily and cheaply with do-it-yourself reflectors; e.g.,

Best and cheapest tend to be mutually exclusively -- it's almost always a tradeoff.

See the wiki below for lots of helpful information.

• posted

1950's would probably be gypsum board or compressed wood waste. You can sorta tell by banging on them. You can be fairly sure by climbing into the attic and looking at the edges. Gypsum board, drywall, and cement (concrete) filled board, vary radically in attenuation and are near the high end (-9dB/wall) of the scale. Vegetable board, compressed wood waste, are near the low end (-4dB/wall).

The added 50cm of hollow core door isn't going to block much. Same with the clothes in the closet (unless someone fills it with junk). However, each little obstruction adds more loss and reflections.

Well, if you're planning on wiring the apartments, you might consider also wiring the middle apartment. This way, you can divide the \$100/month fee by 3 instead of half.

Thanks. However, note that there was considerable guesswork involved. The method works as I've used it in the past. However, different wireless routers and wireless devices have radically different ranges. I sometimes use one for testing, but when I install the real thing, the ranges are quite different. Antenna locations and positioning also have a huge effect.

Borrow, not buy. If you can't find a wireless router, two laptops, setup in peer to peer (ad-hoc) networking mode will barely suffice. You can also borrow a working router. No need to change any settings or plug it into the internet. Just ping the router's IP address and get a feel for the packet loss. Fairly low and consistent (1-3msec) ping latency is good. Higher numbers, wide variations, or lost packets, are a sign of problems. If you want to benchmark the wireless connection, try IPERF and/or JPERF.

Wire is also more reliable, more secure, and the best choice. Use wireless where wiring is impossible.

A directional antenna at both end and pointed towards each other will certainly help. Directional antennas also dramatically reduce reflections, and interference sources that are to the sides and back of the antennas. However, if you're unlucky enough to have an interference source that's inline with your directional antennas, the antenna gain will make it worse. That's also why you don't want to put a wireless device in a window. You'll pickup too much junk from the rest of the city.

Thanks again.

Good luck. Try the wireless, but if that doesn't look promising, do the wiring.

• posted

Regarding the lost flexibility aspect, I like the idea of running Ethernet cable between two (or three, if the middle flat is included) permanent outlets, and then using each of the permanent outlets as a transition point to wireless. That way each AP is within the same flat that it services, one AP per flat.

Cabling-Design.com Forums website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.