two antennas

Been searching for a while now.. I figure it's time to ask..

What are the two antennas on AP's (so equipped) for?

I'm in the Netherlands in a 3 story (with stressed concrete floors) house.
If I were to take one of the antennas off and dangle it out my window to the
bottom floor on 10 feet of coax, would I be able to get WiFi on my top
(where the AP with one antenna would be) and bottom floors?

Or... I've seen pictures of parabolic reflectors on the antennas. Would
this punch through 2 floors of stressed concrete?

I've not bought a WiFi router yet, so any suggestions as to which types to
buy and other suggestions for making wireless work to an IBM T40 laptop
(with internal screen mounted 802.11b antennas) would be appreciated.

Thanks in Advance.

Al...

The two antennas are almost certainly for spatial diversity reception,
based on the probability that the signal strength will not be equally
bad at two different locations at the same time.

-=-
Alan


On 09/09/03 09:39 am Al Adrian put fingers to keyboard and launched the
following message into cyberspace:

> Been searching for a while now.. I figure it's time to ask..
>
> What are the two antennas on AP's (so equipped) for?

In message <vKk7b.262527$(E-Mail Removed)>, Al Adrian
<ara__@SPAMNOTwanadoo.nl> writes
>Been searching for a while now.. I figure it's time to ask..
>
>What are the two antennas on AP's (so equipped) for?

I could speculate, but no doubt someone will come in with this one. My
AP has only one.
>
>I'm in the Netherlands in a 3 story (with stressed concrete floors) house.
>If I were to take one of the antennas off and dangle it out my window to the
>bottom floor on 10 feet of coax, would I be able to get WiFi on my top
>(where the AP with one antenna would be) and bottom floors?

Might get a little cold in the winter with the window open :-)
>
>Or... I've seen pictures of parabolic reflectors on the antennas. Would
>this punch through 2 floors of stressed concrete?

Not sure, but I think probably. There's been some threads (with links)
recently here about home-brewed reflectors and I've had considerable
success. About one and a half miles using one at each end from indoors
to indoors (brick-built walls).
>
>I've not bought a WiFi router yet, so any suggestions as to which types to
>buy and other suggestions for making wireless work to an IBM T40 laptop
>(with internal screen mounted 802.11b antennas) would be appreciated.

As you appear to have a wireless-enabled laptop, you won't be using one
of these PCMIA/Cardbus wireless cards will you (poor range).

FWIW, because I've on ADSL I've got a Netgear DG824M on my PC and a
Linksys WUSB11 on my laptop. Very easy to install, no problems, and very
good range - that's my view of what networks should be :-)
--
Tony Morgan
Smile in the face of adversity - and adversity will probably
think you're taking the piss and kick the shit out of you.

> I could speculate, but no doubt someone will come in with this one. My
> AP has only one.

Open up the case, my bet is that there's a PCB track which is the second
antenna.

David.

In message <(E-Mail Removed)>, David Taylor
<(E-Mail Removed)> writes
>> I could speculate, but no doubt someone will come in with this one. My
>> AP has only one.
>
>Open up the case, my bet is that there's a PCB track which is the second
>antenna.

I thought that the ones with a single aerial were half-wave ground-pane
dipoles possibly with a quarter-wave shorted stub to provide matching
for off-centre-band channels. The shorted stub might be tracked on the
PCB

When there are two aerials and the distance between them is
approximately the same height as the elements I'd speculate that they
were a simple half-wave phased array - perhaps to give lobes to left and
right instead of the usual omni plot.
--
Tony Morgan
Smile in the face of adversity - and adversity will probably
think you're taking the piss and kick the shit out of you.

Easy answer,
you use 2 antenna's to combat null signals. In short, if you send signals
through an enviorment that has many reflectors (walls, buildings, etc) where
the 2 signals cross each other is going to be a null zone where the signals
have cancelled each other out. By using 2 antenna's your access point can
utilize the antenna that is recieving the best signal.

Colin McNamara

"Tony Morgan" <(E-Mail Removed)> wrote in message
newsTZDACHeclX$(E-Mail Removed)...
> In message <(E-Mail Removed)>, David Taylor
> <(E-Mail Removed)> writes
> >> I could speculate, but no doubt someone will come in with this one. My
> >> AP has only one.
> >
> >Open up the case, my bet is that there's a PCB track which is the second
> >antenna.
>
> I thought that the ones with a single aerial were half-wave ground-pane
> dipoles possibly with a quarter-wave shorted stub to provide matching
> for off-centre-band channels. The shorted stub might be tracked on the
> PCB
>
> When there are two aerials and the distance between them is
> approximately the same height as the elements I'd speculate that they
> were a simple half-wave phased array - perhaps to give lobes to left and
> right instead of the usual omni plot.
> --
> Tony Morgan
> Smile in the face of adversity - and adversity will probably
> think you're taking the piss and kick the shit out of you.

> I thought that the ones with a single aerial were half-wave ground-pane
> dipoles possibly with a quarter-wave shorted stub to provide matching
> for off-centre-band channels. The shorted stub might be tracked on the
> PCB

Well on the ones I've seen, they generally find their way back to the
diversity switch which would suggest the two.

David.

In message <GUy7b.1556$(E-Mail Removed)>, Colin McNamara
<(E-Mail Removed)> writes
>Easy answer,
>you use 2 antenna's to combat null signals. In short, if you send
>signals through an enviorment that has many reflectors (walls,
>buildings, etc) where the 2 signals cross each other is going to be a
>null zone where the signals have cancelled each other out. By using 2
>antenna's your access point can utilize the antenna that is recieving
>the best signal.

So you're saying that APs with two aerial have two Tx and two Rx signal
circuit channels?

Hmmm... I doubt it. As I suggested it's far more likely to be the use of
a single cardiod plot for both Tx and Rx that results from a simple
phased array. With this you can use the cardiod plot to null out
unwanted signals.

Simple phased arrays like this, BTW have long been used by aircraft ILS
systems - since WW2 in fact. Not exactly rocket-science :-)
--
Tony Morgan
Smile in the face of adversity - and adversity will probably
think you're taking the piss and kick the shit out of you.

In message <GZ2oylCiruX$(E-Mail Removed)>, Tony Morgan
<(E-Mail Removed)> writes
>Simple phased arrays like this, BTW have long been used by aircraft ILS
>systems - since WW2 in fact. Not exactly rocket-science :-)

Thinking about it, its also always been (and still is) used for SARBE
(search and rescue equipment).
--
Tony Morgan
Smile in the face of adversity - and adversity will probably
think you're taking the piss and kick the shit out of you.

> So you're saying that APs with two aerial have two Tx and two Rx signal
> circuit channels?
>
> Hmmm... I doubt it. As I suggested it's far more likely to be the use of
> a single cardiod plot for both Tx and Rx that results from a simple
> phased array. With this you can use the cardiod plot to null out
> unwanted signals.

No, used for diversity switching to resolve problems with multipath
signal issues.

The diversity switch will select the antenna which is receiving the
strongest signal.

Here's a pic of a Dlink DWL900+, one external dipole antenna, the other
clearly inside. Both connect to the PCMCIA card.

http://www.nodomainname.co.uk/dwl900+/dwl900+.jpg

On the PCMCIA card, there's this little diversity blob bang in the
middle on the left (6 pin component):-

http://www.nodomainname.co.uk/ma401/ma401lower.jpg

David.