AP External Antenna question?

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

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
6 answers Last reply
More about external antenna question
  1. 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.
  2. Archived from groups: alt.internet.wireless (More info?)

    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
  3. 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
  4. 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.
  5. 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/
  6. 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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