AP External Antenna question?

G

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I want to install outdoor antennas to make connection between AP and Bridge.
The Linksys devices each have 2 antennas. Do I have to install 2 outdoor
antennas for one device? Some of Dlink's devices have only one antenna. What
is the diffence between the two antennas device and the one antenna device?
Thank you.
GL
 
G

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Archived from groups: alt.internet.wireless (More info?)

"G Lam" <No_spam@anywhere.com> wrote in message
news:Gq6dndl-io19XSHcRVn-gw@comcast.com...
> I want to install outdoor antennas to make connection between AP and
Bridge.
> The Linksys devices each have 2 antennas. Do I have to install 2 outdoor
> antennas for one device? Some of Dlink's devices have only one antenna.
What
> is the diffence between the two antennas device and the one antenna
device?
> Thank you.
> GL
>
>

Dual antennas is called diversity and is used to compensate for multipath
interference (reflections).
The antenna with the strongest signal at that instant is used to receive and
re-transmit the next frames.
In your case you wont use diversity.Some APs allow you to turn off diversity
and to select which antenna to use
(left or right). MyLinksys WAP54g has this option.
 
G

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On Sun, 12 Dec 2004 17:09:06 -0500, "G Lam" <No_spam@anywhere.com>
wrote:

>I want to install outdoor antennas to make connection between AP and Bridge.
>The Linksys devices each have 2 antennas. Do I have to install 2 outdoor
>antennas for one device? Some of Dlink's devices have only one antenna. What
>is the diffence between the two antennas device and the one antenna device?

You only need or want one external antenna. The two antennas are for
diversity reception, where the router selects which antenna has the
best reception. The idea is to help deal with multipath and
reflections. You can do that with two outdoor antennas, but it's
neither necessary, or particularly desireable.

Once catch with your unspecified Linksys wireless device (why do you
keep the model number secret), is that some wireless devices transit
on only one of the antennas, while doing the diversity receive thing
using both antennas. I can never remember which antenna and am too
lazy to figure out which models. Just try one antenna and if it
doesn't work quite right, try the other.

Another piece of trivia is that the cable lengths inside the box on
many routers are different between the two antennas. Find a picture
of the inside of your router, and select the antenna with the shortest
coax, or preferably, no coax cable. That's worth about 1dB which
might make a difference on a long distance link.

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
 
G

Guest

Guest
Archived from groups: alt.internet.wireless (More info?)

I have not bought any Linksys or Dlink device yet. I plan to implement a
Wifi connection between two buildings 1600ft apart. External antennas are
needed in my case to shot up the signal strength. I have to figure out what
to buy and how to install the antennas up front. I want to use 9dbi gain
antenna with 2 db cable/connector loss on each end; hopefully, I can get a
total of 14 dbi gain.
Thank you for your valuable information. It really helps.
GL

"Jeff Liebermann" <jeffl@comix.santa-cruz.ca.us> ???
news:julpr0p9p8sorcffubf9r32gishilhedr4@4ax.com ???...
> On Sun, 12 Dec 2004 17:09:06 -0500, "G Lam" <No_spam@anywhere.com>
> wrote:
>
> >I want to install outdoor antennas to make connection between AP and
Bridge.
> >The Linksys devices each have 2 antennas. Do I have to install 2 outdoor
> >antennas for one device? Some of Dlink's devices have only one antenna.
What
> >is the diffence between the two antennas device and the one antenna
device?
>
> You only need or want one external antenna. The two antennas are for
> diversity reception, where the router selects which antenna has the
> best reception. The idea is to help deal with multipath and
> reflections. You can do that with two outdoor antennas, but it's
> neither necessary, or particularly desireable.
>
> Once catch with your unspecified Linksys wireless device (why do you
> keep the model number secret), is that some wireless devices transit
> on only one of the antennas, while doing the diversity receive thing
> using both antennas. I can never remember which antenna and am too
> lazy to figure out which models. Just try one antenna and if it
> doesn't work quite right, try the other.
>
> Another piece of trivia is that the cable lengths inside the box on
> many routers are different between the two antennas. Find a picture
> of the inside of your router, and select the antenna with the shortest
> coax, or preferably, no coax cable. That's worth about 1dB which
> might make a difference on a long distance link.
>
> --
> Jeff Liebermann jeffl@comix.santa-cruz.ca.us
> 150 Felker St #D http://www.LearnByDestroying.com
> Santa Cruz CA 95060 AE6KS 831-336-2558
 
G

Guest

Guest
Archived from groups: alt.internet.wireless (More info?)

On 12/13/04 12:48 AM, Jeff Liebermann wrote:

> Once catch with your unspecified Linksys wireless device (why do you
> keep the model number secret), is that some wireless devices transit
> on only one of the antennas, while doing the diversity receive thing
> using both antennas. I can never remember which antenna and am too
> lazy to figure out which models. Just try one antenna and if it
> doesn't work quite right, try the other.

Do you know if the LinkSys WRT54GS V1.0 transmits only using one of the
antennas?

> Another piece of trivia is that the cable lengths inside the box on
> many routers are different between the two antennas. Find a picture
> of the inside of your router, and select the antenna with the shortest
> coax, or preferably, no coax cable. That's worth about 1dB which
> might make a difference on a long distance link.

That's a great tip!
It looks like I should use the right antenna on the LinkSys WRT54GS
V1.0, since it doesn't use no coax cable:
<http://www.linksysinfo.org/modules/Content/Autopsy/WRT54GS-mblg.jpg>

Thanks.
 
G

Guest

Guest
Archived from groups: alt.internet.wireless (More info?)

> Another piece of trivia is that the cable lengths inside the box on
> many routers are different between the two antennas. Find a picture
> of the inside of your router, and select the antenna with the
shortest
> coax, or preferably, no coax cable. That's worth about 1dB which
> might make a difference on a long distance link.
>
> --
> Jeff Liebermann jeffl@comix.santa-cruz.ca.us
> 150 Felker St #D 'http://www.LearnByDestroying.com'
(http://www.learnbydestroying.com/)
> Santa Cruz CA 95060 AE6KS 831-336-2558

This is also for antenna "co-phasing" or matching the two antennas to the
load.

Do not change the length!!!!


--
viradio
brought to you by http://www.wifi-forum.com/
 
G

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Archived from groups: alt.internet.wireless (More info?)

On Sun, 26 Dec 2004 12:45:20 GMT, viradio
<viradio.1hvggy@WiFi-Forum_dot_com> wrote:

>> Another piece of trivia is that the cable lengths inside the box on
>> many routers are different between the two antennas. Find a picture
>> of the inside of your router, and select the antenna with the
>shortest
>> coax, or preferably, no coax cable. That's worth about 1dB which
>> might make a difference on a long distance link.

>This is also for antenna "co-phasing" or matching the two antennas to the
>load.
>Do not change the length!!!!

Wrong. Co-phasing is a term used (almost) exclusively in CB radios.
http://www.signalengineering.com/ultimate/co_phasing.html
It is also used in astronomy to describe the alignment requirement of
segmented telescope mirrors.

Co-phasing is applicable for dual CB antennas, and other such
abominations, because both antennas are operated simultaneously. This
results in some "interesting" antenna patterns and cable length
requirements to get a proper impedance match. The coax cable "phasing
harness" allegedly forms a power splitter, where the cable lengths are
critical.

However, the wireless access point has one additional piece of
circuitry that is lacking in a typical CB radio and antenna system.
It has a diversity switch located between the antennas and the radio.
The switch scans between the two antennas, looking for the best
receive signal. The algorithm varies by chipset, but is basically a
stored antenna selection based upon the last successfully received
packet.

When one antenna is selected and active, the other antenna is isolated
from the radio and shorted to ground by the PIN diode switch diversity
switch. However, the antennas are in sufficient proximity to create a
somewhat directional pattern, and I agree that this pattern is highly
dependent upon the length of internal coax cables. However, it is NOT
critical by any stretch of the imagination, as demonstrated by the
ability to orient the two antennas in any random manner and still have
a functional access point. One can even remove or short one of the
antennas, and see little effect on performance.

Anyway, since the coax cables are NOT part of some phasing, matching,
power splitting, or beam forming network, and are impedance matched at
both ends, the actual lengths are NOT critical.

Incidentally, I never suggested changing the length of the internal
coax cable. My comments were in reference to the loss between the
radio assembly and the antenna being slightly less on the port without
the added loss of the coax cable. You are probably correct about not
changing the internal coax cable length. I see some things in the
circuit that look like the diversity switch is running at a much
higher impedance than 50 ohms (to reduce switch loss), and that the
coax cable (and a few components near the antenna connector without
the coax) are part of a matching network. That will make the coax
cable length critical to insure 50 ohms at the connector.


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
 

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