WiFi through walls - Directional vs Omni Directional

Do directional antennas only do well in line-of-sight situations?

I need to go through about 4 or 5 walls to get to my router. Would I
do better replacing my NIC's 2 dBi omni-directional antenna with a 7
dBi, or would I have better luck with a 12 dBi directional antenna
aimed at the router (through a bunch of walls)?

Depends how the signal is getting through the wall!

Broadly speaking you can have two types of directional antenna: one which is
still omnidirectional in the horizontal plane with increased gain, at the
expense of the vertical plane which is reduced, i.e. isn't very sensitive to
signals coming in from above it.

The other is increased sensitivity in both horizontal and vertical planes (a
bit like the inverse of a searchlight).

So if you can "point" towards where most of the signal is entering the room
you will get an improvement.

HTH Regards, Charles

"Dennis" <(E-Mail Removed)> wrote in message
news:92a6ef30-3a9a-4dd9-8911-(E-Mail Removed)...
> Do directional antennas only do well in line-of-sight situations?
>
> I need to go through about 4 or 5 walls to get to my router. Would I
> do better replacing my NIC's 2 dBi omni-directional antenna with a 7
> dBi, or would I have better luck with a 12 dBi directional antenna
> aimed at the router (through a bunch of walls)?
>

"Dennis" <(E-Mail Removed)> wrote in message
news:92a6ef30-3a9a-4dd9-8911-(E-Mail Removed)...
> Do directional antennas only do well in line-of-sight situations?
>
> I need to go through about 4 or 5 walls to get to my router. Would I
> do better replacing my NIC's 2 dBi omni-directional antenna with a 7
> dBi, or would I have better luck with a 12 dBi directional antenna
> aimed at the router (through a bunch of walls)?
>
I had a very similar problem recently. wifi hates walls, especially 4 or 5 of them. If you
have no luck connecting with your 7db antenna try network-over-mains.
I'm in the UK and I got these:
http://www.wirelesspro.co.uk/product..._homeplug_kit/
If you're outside the UK there must be an equivalent for your country.
They great, and really are plug and play. There's no set up, no configuring, just plug
them in connect the ethernets at each end and you're away.

On Sat, 7 Jun 2008 14:05:55 -0700 (PDT), Dennis
<(E-Mail Removed)> wrote:

>Do directional antennas only do well in line-of-sight situations?

No. Directional antennas can be used for non-line-o-site situations.

>I need to go through about 4 or 5 walls to get to my router.

Give up now, while you're still sane. Unless the walls are made of
paper, it's not going to work. Most walls are good for considerable
losses. If there's aluminum foil backed insulation in the walls,
nothing gets through. Fairly lossy with poured concrete and chicken
wire backed stucco or lath and plaster.

>Would I
>do better replacing my NIC's 2 dBi omni-directional antenna with a 7
>dBi, or would I have better luck with a 12 dBi directional antenna
>aimed at the router (through a bunch of walls)?

Neither. Drill a hole under the trim and run CAT5. When you move
out, patch the holes with spackle, and replace the trim. Nobody will
notice. Also CAT5e in flat cables which does nicely through cracks,
under carpets, the under doors. If impossible, think about power line
networking.



--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Jun 7, 6:59*pm, Jeff Liebermann <je...@cruzio.com> wrote:
> On Sat, 7 Jun 2008 14:05:55 -0700 (PDT), Dennis
>
> <dennispub...@hotmail.com> wrote:
> >Do directional antennas only do well in line-of-sight situations?
>
> No. *Directional antennas can be used for non-line-o-site situations.
>
> >I need to go through about 4 or 5 walls to get to my router.
>
> Give up now, while you're still sane. *Unless the walls are made of
> paper, it's not going to work. *Most walls are good for considerable
> losses. *If there's aluminum foil backed insulation in the walls,
> nothing gets through. *Fairly lossy with poured concrete and chicken
> wire backed stucco or lath and plaster.
>
> >Would I
> >do better replacing my NIC's 2 dBi omni-directional antenna with a 7
> >dBi, or would I have better luck with a 12 dBi directional antenna
> >aimed at the router (through a bunch of walls)?
>
> Neither. *Drill a hole under the trim and run CAT5. *When you move
> out, patch the holes with spackle, and replace the trim. *Nobody will
> notice. *Also CAT5e in flat cables which does nicely through cracks,
> under carpets, the under doors. *If impossible, think about power line
> networking.



I should have been more clear. This is not mission impossible. Even
with my 2 dBi antenna I am receiving a signal, at about 15% strength.
Perhaps do to multipath, open doors and open windows, but I am getting
something.
Enough to surf the web, slowly...

See this YouTube video: http://www.youtube.com/watch?v=vJwOpJjYKqA

That's kinna what got me thinking about it. He's a directional setup
to go through walls, he picks up 200+ access points at one point. Very
interesting. Granted its a *completely* different situation, but I
dont think his results would be nearly as good with any kind of omni-
directional setup.

On Sat, 7 Jun 2008 16:36:31 -0700 (PDT), Dennis
<(E-Mail Removed)> wrote:

>I should have been more clear. This is not mission impossible. Even
>with my 2 dBi antenna I am receiving a signal, at about 15% strength.
>Perhaps do to multipath, open doors and open windows, but I am getting
>something.

What type of walls? Usually, one wall is no problem. Two walls are
possible. Three or more walls are usually a problem. You're correct
and probably are dealing with multipath and reflections. The problem
with such a path is that it's not reliable. You're going to be
adjusting your antenna every time someone moves something. It's
really not reliable, no matter how strong the signal.

There's also some question as to where to point it. Directly towards
the access point is the obvious start, but if you're dealing with
reflections, other less obvious directions, might work better. If
this is the case, they won't stay working as the reflections tend to
move around. You will probably be constantly adjusting the antenna.

>Enough to surf the web, slowly...

What do you have for equipment? USB, PCI, laptop, or what? If it's a
USB or laptop, almost any manner of external antenna is better than
what comes stock. The gain of the USB devices are typically about
-2dBi. Yeah, it's negative as in a net loss of power. Literally any
external antenna is better than that.

Same with some laptops, but for a different reason. The thin coax
cable going between the wi-fi card in the base, and the diversity
antennas near the top of the LCD, is rather lossy. There are also
some laptops that stupidly install the antenna in the hinge, which is
really bad for performance:
<http://802.11junk.com/jeffl/antennas/laptops/slides/compaq-2120us.html>

Whatcha got to work with in the way of hardware?

>See this YouTube video: http://www.youtube.com/watch?v=vJwOpJjYKqA

The guy is probably half way up the high rise apartments in the photo
and is looking out over a very large area, with plenty more wireless
devices. He could be using just the USB dongle, and probably get a
substantial number of access points. It would have been interesting
if he had run the same test with just the USB dongle fpr comparison.

I did the numbers for such a contrivance in the past.
<http://groups.google.com/group/alt.internet.wireless/msg/bae6f7c6d35160d0>
19.5dBi maximum gain for a 0.6 meter dish. That's probably high
considering that the illumination angle of the coffee can feed, does
not match that of the dish, and the illumination pattern of the USB
device does not match that of the coffee can. Still, my guess(tm) is
that a gain of 15dBi can be achieved with such a setup.

>That's kinna what got me thinking about it. He's a directional setup
>to go through walls, he picks up 200+ access points at one point. Very
>interesting. Granted its a *completely* different situation, but I
>dont think his results would be nearly as good with any kind of omni-
>directional setup.

Do you really want that mess indoors? If not, look into panel
antennas, which are less aesthetically disgusting.

Anyway, it's worth trying. The setup in the YouTube video is better
than most construction articles. This one is also tolerable:
<http://www.weijand.nl/wifi/>
However, methinks you should try a different flavor of reflector
before bulding something like the YouTube video. See:
<http://www.freeantennas.com>
for various simple reflectors (that work).

--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Lots of good info there Jeff, thanks its appreciated.

For fun I went out and grabbed a $20 omni antenna, it claims to be 9
dBi... I figured for $20 it was worth a shot... Until I realized I'd
also need an SMC cable.. the new antenna needs to be raised away from
the case of the computer like the old 2 dBi one was.... surfing the
net I'm now realizing the cable is going to cost more then the antenna
did

Which brings me to my next question: How much loss is there per foot
of cable (50 ohm) I use? Is it significant enough for me to want to
get the shortest cable possible, or can I give myself some leeway and
get a 20-30 foot cable?

Dennis wrote:
> Lots of good info there Jeff, thanks its appreciated.
>
> For fun I went out and grabbed a $20 omni antenna, it claims to be 9
> dBi... I figured for $20 it was worth a shot... Until I realized I'd
> also need an SMC cable.. the new antenna needs to be raised away from
> the case of the computer like the old 2 dBi one was.... surfing the
> net I'm now realizing the cable is going to cost more then the antenna
> did
>
> Which brings me to my next question: How much loss is there per foot
> of cable (50 ohm) I use? Is it significant enough for me to want to
> get the shortest cable possible, or can I give myself some leeway and
> get a 20-30 foot cable?

at the Wifi freqs - 2.4Ghz microwave - there is a LOT of loss per foot.
Here's a chart for common LMR type cables ...
http://www.universalweb.com/CustomCa...mCablesUSA.pdf

On Jun 9, 8:03 pm, Dennis <dennispub...@hotmail.com> wrote:
> How much loss is there per foot
> of cable (50 ohm) I use? Is it significant enough for me to want to
> get the shortest cable possible, or can I give myself some leeway and
> get a 20-30 foot cable?


Short answer is: LMR 400 loses .25 db per meter or 6.6 for 100 feet.
30 foot cable is only 2 db. Hawking has a 30 ft 400 that can be
found for $30. Will need a pigtail-adapter, too.

You can use this to determine loss for a given cable:
http://www.timesmicrowave.com/cgi-bin/calculate.pl

Enter 2400 Mhz for frequency if you using B or G.

>. the new antenna needs to be raised away from
>the case of the computer like the old 2 dBi one was....
>I'm now realizing the cable is going to cost more then the antenna
> did

You could use your existing cable for testing and just get an adapter
to start?