Re: How many walls can wifi transmit through?

On Tue, 9 Jun 2009 17:25:44 -0700 (PDT), iconoclastical
<FreeRadical101@xxxxxxxxx> wrote:

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.

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).

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.

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.

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.

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.

I liked you thorough treatment and maths above though,

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.

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.

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.

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.

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

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.

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.

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 :-)

Thanks again.

Grant

Good luck. Try the wireless, but if that doesn't look promising, do
the wiring.
--
Jeff Liebermann jeffl@xxxxxxxxxx
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
.

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