DIY WiFi antenna (to increase reception)

Hi, I kinda new to wireless networking but wanted to find out if it was
possible to make an antenna that increases the range of signals my
notebook can receive. I have looked around and most antennas that I
have seen are for increasing the range of a network (the sending of the
signals?) not necessarily for reception... or if it works for
transmission would it also work for reception? Is it possible to build
(or buy on the cheap) some sort of omni-directional antenna that will
allow me to receive signals that are far away? Any help would be
greatly appreciated!

Cheers

-Gaiko

<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
>
>
> Hi, I kinda new to wireless networking but wanted to find out if it was
> possible to make an antenna that increases the range of signals my
> notebook can receive. I have looked around and most antennas that I
> have seen are for increasing the range of a network (the sending of the
> signals?) not necessarily for reception... or if it works for
> transmission would it also work for reception? Is it possible to build
> (or buy on the cheap) some sort of omni-directional antenna that will
> allow me to receive signals that are far away? Any help would be
> greatly appreciated!
>
> Cheers
>
> -Gaiko
>

Construct a metal parabola with a focal point that is
1/2 * (C/2.4 Ghz) ...( about 2.27 inches) from the
surface of the parabola. Then place your antenna at the
focal point, and point the parabola at the transmitter :-)

You can also construct similar antennas for cell phones....

Enjoy,
Postmaster

(E-Mail Removed) wrote:
>Hi, I kinda new to wireless networking but wanted to find out if it was
>possible to make an antenna that increases the range of signals my
>notebook can receive. I have looked around and most antennas that I
>have seen are for increasing the range of a network (the sending of the
>signals?) not necessarily for reception... or if it works for
>transmission would it also work for reception?

Yes, it is reciprocal, and any improvement in transmission will be
identical to the improvement for reception.

(Note that increasing the transmit power of an Access Point might
be possible too, but has exactly the effect you are concerned with,
because it has value in one direction only.)

>Is it possible to build
>(or buy on the cheap) some sort of omni-directional antenna that will
>allow me to receive signals that are far away? Any help would be
>greatly appreciated!

Definitely! Just be warned that high gain omni-directional
antennas are not simple, and not inexpensive.

Let me provide a few technical details that you need in order to
understand what you'll be looking at.

First, antennas are measured in numbers called "dBi", which is a
logarithmic ratio. The 'd' for deci, or 1/10th. the 'B' is for
Bell, the name of the guy who came up with it. You'll see all
kinds of dB ratios used in radio work. As just dB, it's a
ratio. With a letter after it, it's a ratio compared to
something specific. The 'i' stands for a point source antenna
in outer space, called an "isotropic radiator". It's a truly
omni-directional antenna, and no such thing exists in reality.
This (imaginary) isotropic radiator as 0 dBi gain.

What you'll see called "omni" antennas are omni-directional
around the points of a compass (azimuth), but not vertically.
That's good, because you don't want to waste your radio's power
by transmitting it directly up, or directly down. Instead, that
power is redirected perpendicular to the antenna, which gives it
gain in those directions.

Because of that, a plain old every day omni antenna has a gain
of about 2 dBi. And everything else you see, you will want to
compare to that. The comparison is that a 6 dB increase in
signal strength (3 dB is twice as much power, because dB's are
logarithmic, so 6 dB is 4 times as much power) will just about
double the range of a radio link. Hence if you can walk down
the road 300 feet before you lose your connection, if you switch
from a 2 dBi antenna to an 8 dBi antenna you would probably be
able to go about 600 feet before losing the connection.

You can buy 7 dBi (almost a 6 dB increase) antennas for something
like $40 or so. More gain than that in an omni requires some
significant hardware, and will cost relatively more.

"Directional antennas", where that means directional in azimuth
instead of only in elevation, are much easier to get a lot of
gain from, and hence are less expensive (but don't do you much
good either).

There are other considerations too. The higher the antenna, the
farther it's view will be. Also the fewer obstructions, the
better. It happens that 802.11b/g wireless uses 2400MHz, and
at that frequency almost *anything* absorbs radio signals. Trees,
walls, and basically anything you can't see through. So locate
your Access Point accordingly!

--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) (E-Mail Removed)

<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
>
>
> Hi, I kinda new to wireless networking but wanted to find out if it was
> possible to make an antenna that increases the range of signals my
> notebook can receive. I have looked around and most antennas that I
> have seen are for increasing the range of a network (the sending of the
> signals?) not necessarily for reception... or if it works for
> transmission would it also work for reception? Is it possible to build
> (or buy on the cheap) some sort of omni-directional antenna that will
> allow me to receive signals that are far away? Any help would be
> greatly appreciated!
>
> Cheers
>
> -Gaiko
>

A few more details:

You'll need a 9 inch piece of cardboard,
and some aluminum foil. Then create a parabola
See:
http://www.sciences.univ-nantes.fr/p...ra_string.html

Be sure that the focal point is ~ 2.267 inches from the nearest
point on the parabola. Now cover your cardboard with the foil,
and bend into the parabola that you just drew. Put the wireless
antenna at 'F' ( the focal point ) and point this at the nearest
access point. You got it...

Note: You can create two parabola shapes out of a piece
of cardboard, and bend the aluminum foil/cardboard around
these two pieces. Then glue, to hold it in place.

Nothing like a bit of math and a homebrew project to add
fun to computing :-)


Enjoy,
Postmaster

(E-Mail Removed) (Floyd L. Davidson) writes:


>What you'll see called "omni" antennas are omni-directional
>around the points of a compass (azimuth), but not vertically.
>That's good, because you don't want to waste your radio's power
>by transmitting it directly up, or directly down. Instead, that
>power is redirected perpendicular to the antenna, which gives it
>gain in those directions.

This however also means that you cannot have it on a laptop which you then
operate on your lap--ie with the perpendicular of the antenna pointing
everywhich way. The antenna must be oriented so that the perp (axis) really
is perpendicular, or you will get less, rather than more gain. The higher
the gain the worst this is.

"Postmaster" <postmaster@127.0.0.1> wrote in message
news:2%2qe.7749$Kj3.1492@trnddc03...

>> Is it possible to build
>> (or buy on the cheap) some sort of omni-directional antenna that will
>> allow me to receive signals that are far away? Any help would be
>> greatly appreciated!

> A few more details:
[...]
> Be sure that the focal point is ~ 2.267 inches from the nearest
> point on the parabola. Now cover your cardboard with the foil,
> and bend into the parabola that you just drew. Put the wireless
> antenna at 'F' ( the focal point ) and point this at the nearest
> access point. You got it...

You should look up the definition of "omni-directional".

Unruh <unruh-(E-Mail Removed)> wrote:
>(E-Mail Removed) (Floyd L. Davidson) writes:
>
>>What you'll see called "omni" antennas are omni-directional
>>around the points of a compass (azimuth), but not vertically.
>>That's good, because you don't want to waste your radio's power
>>by transmitting it directly up, or directly down. Instead, that
>>power is redirected perpendicular to the antenna, which gives it
>>gain in those directions.
>
>This however also means that you cannot have it on a laptop which you then
>operate on your lap--ie with the perpendicular of the antenna pointing
>everywhich way. The antenna must be oriented so that the perp (axis) really
>is perpendicular, or you will get less, rather than more gain. The higher
>the gain the worst this is.

True, but even *worse* than you are saying!

2.4GHz RF will bounce off any metal object larger than about 3"
square, hence there are bound to be lots of reflected signals in
almost any environment. In some cases one of those reflected
signals is likely to be the strongest signal. Because it is
reflected, it no longer necessarily has vertical polarization,
and might just be almost anything.

If you put the laptop in your lap, and tilt one way... you may
get an increase in signal, but tilting in some other direction
may get an even deeper fade than just having it sitting straight
a level. And of source in many laptops the antenna is in the
lid, which isn't necessarily straight up and down either!

What it all boils down to is that having a good line of sight
location only a short distance from the Access Point is best,
and for anything else a little experimentation with orientation
might do wonders if there is a marginal connection.

--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) (E-Mail Removed)

"ynotssor" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
>
> "Postmaster" <postmaster@127.0.0.1> wrote in message
> news:2%2qe.7749$Kj3.1492@trnddc03...
>
>>> Is it possible to build
>>> (or buy on the cheap) some sort of omni-directional antenna that will
>>> allow me to receive signals that are far away? Any help would be
>>> greatly appreciated!
>
>> A few more details:
> [...]
>> Be sure that the focal point is ~ 2.267 inches from the nearest
>> point on the parabola. Now cover your cardboard with the foil,
>> and bend into the parabola that you just drew. Put the wireless
>> antenna at 'F' ( the focal point ) and point this at the nearest
>> access point. You got it...
>
> You should look up the definition of "omni-directional".
>

One may find that a directional antenna, pointed at the
access point, can greatly improve range. If the antenna
is lite, and easily turned, one can quickly find the access
point and be a happy camper :-) The method above
increases the range by a rather significant distance....
In some cases, around 1/2 mile !

Enjoy,
Postmaster.

(E-Mail Removed) wrote:

>
>
> Hi, I kinda new to wireless networking but wanted to find out if it was
> possible to make an antenna that increases the range of signals my
> notebook can receive. I have looked around and most antennas that I
> have seen are for increasing the range of a network (the sending of the
> signals?) not necessarily for reception... or if it works for
> transmission would it also work for reception? Is it possible to build
> (or buy on the cheap) some sort of omni-directional antenna that will
> allow me to receive signals that are far away? Any help would be
> greatly appreciated!

With very few exceptions, antennas work equally well for transmission and
reception. Now what you're looking for is gain, which involves tradeoffs.
You get more signal in one direction, only by reducing it in others. With
a standard vertical antenna, you'll have a donut shaped pattern. With an
omnidirectional gain antenna, you'll have a squashed donut, where range is
extended at the expense of signal at higher angles. You can also get
directional antennas, with more gain. However, the more gain, the more
complex (read expensive) the antenna becomes. There are commercial antenna
available and you can roll your own as well. But no matter how you obtain
an external antenna, you'll need some method to connect it. Does your wifi
adapter have a connector, that can be used for an external antenna?

"Postmaster" <postmaster@127.0.0.1> wrote:
>"ynotssor" <(E-Mail Removed)> wrote:
>>
>> You should look up the definition of "omni-directional".
>>
>
> One may find that a directional antenna, pointed at the
> access point, can greatly improve range. If the antenna

The OP has a laptop, with a builtin wifi client. He could go to
a lot of trouble to figure out how to get an external antenna to
work, and it would no doubt cost a wee bit too.

But tell me, is he really going to pack a parabolic around and
set it up everywhere he wants to use the lap top from? I doubt
it.

Perhaps, the appropriate discussion is about what he can do with
high gain omni-directional antennas for the AP.

> is lite, and easily turned, one can quickly find the access
> point and be a happy camper :-) The method above
> increases the range by a rather significant distance....
> In some cases, around 1/2 mile !

And indeed, there is some remote chance that he would be
interested in doing it that way. But you need to point out the
detractions too, such as needing to buy another wifi client and
get one with a connector for an external antenna.

--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) (E-Mail Removed)