# How many walls can wifi transmit through?

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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

Re: How many walls can wifi transmit through?
they do not link direct but go through the router so where is it.

Re: How many walls can wifi transmit through?

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

Re: How many walls can wifi transmit through?
iconoclastical wrote:

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

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Re: How many walls can wifi transmit through?
On Sat, 6 Jun 2009 20:25:40 -0700 (PDT), iconoclastical

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:
<http://wireless.navas.us/wiki/Wi-Fi#Attenuation
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.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Re: How many walls can wifi transmit through?
Jeff Liebermann wrote:

A lurker says thank you.

Lou

Re: How many walls can wifi transmit through?
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)

Re: How many walls can wifi transmit through?
On Sun, 7 Jun 2009 17:30:45 -0500, "dave AKA vwdoc1"

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:
<http://wireless.navas.us/wiki/Wi-Fi_How_To#Use_a_wireless_router_as_a_wireless_access_point
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?

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Re: How many walls can wifi transmit through?
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!  <g>

thanks!
--
later,
(One out of many daves)

<http://wireless.navas.us/wiki/Wi-Fi_How_To#Use_a_wireless_router_as_a_wireless_access_point

Re: How many walls can wifi transmit through?
Thank you Jeff, your posting was very helpful.

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

Thanks again.

Re: How many walls can wifi transmit through?

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.)

Re: How many walls can wifi transmit through?
On Sun, 7 Jun 2009 17:00:23 -0700 (PDT), iconoclastical

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.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Re: How many walls can wifi transmit through?

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

Re: How many walls can wifi transmit through?
On Tue, 9 Jun 2009 17:25:44 -0700 (PDT), iconoclastical

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.
--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Re: How many walls can wifi transmit through?

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)

Re: How many walls can wifi transmit through?
iconoclastical wrote:

...

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.

--
15:26:12 up 34 days, 20:07,  4 users,  load average: 0.10, 0.14, 0.16
A few flakes working together can unleash an avalanche of destruction

Re: How many walls can wifi transmit through?
On Tue, 9 Jun 2009 17:25:44 -0700 (PDT), iconoclastical

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., <http://www.freeantennas.com/

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

See the wiki below for lots of helpful information.

--
Best regards,   FAQ for Wireless Internet: <http://wireless.navas.us
John            FAQ for Wi-Fi:  <http://wireless.navas.us/wiki/Wi-Fi
Wi-Fi How To:  <http://wireless.navas.us/wiki/Wi-Fi_HowTo
Fixes to Wi-Fi Problems:  <http://wireless.navas.us/wiki/Wi-Fi_Fixes

Re: How many walls can wifi transmit through?
On Wed, 10 Jun 2009 08:03:45 -0700, John Navas

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.

Re: How many walls can wifi transmit through?
capww8 had written this in response to
http://forums.cabling-design.com/wireless/How-many-walls-can-wifi-transmit-through-61338-.htm
:
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.

-------------------------------------
iconoclastical wrote:

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