Question: singal strength, same each end?

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

Hi All,

I have an 18db parabolic antenna pointed at a Tin Cantenna about 800 metres
away line of sight.

From the netcard at the cantenna side, I'm getting 40% signal strength. My
access point rarely sees the cantenna however and generally not for very
long.

I've heard the antenna gain is same for send and receive so I take it that
my home made cantenna should be sending something out. Could it be that the
parabolic antenna sends in a wider arc which the cantenna can see but not
vice versa?

There are some tall trees to the immediate right of the line but I can see
the antenna clearly. I've read a little about the "Fersnal zone" and that
you shouldn't point the antennas directly at each other. Could this be
causing dramas?

Thanks for any input.

Jac
6
answers
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More about question singal strength
  1. Archived from groups: alt.internet.wireless (More info?)

    On Tue, 17 Aug 2004 09:37:02 +0800, "Amhir Sohail"
    <amhirsohail@yahoo.com.au> wrote:

    >I have an 18db parabolic antenna pointed at a Tin Cantenna about 800 metres
    >away line of sight.
    >
    >From the netcard at the cantenna side, I'm getting 40% signal strength. My
    >access point rarely sees the cantenna however and generally not for very
    >long.

    Ok, something is wrong. If you move closer with the hardware, can the
    access point eventually pickup the signal? Just checking if things
    are properly configured.

    >I've heard the antenna gain is same for send and receive so I take it that
    >my home made cantenna should be sending something out. Could it be that the
    >parabolic antenna sends in a wider arc which the cantenna can see but not
    >vice versa?

    Transmit and receive gains are identical. The antenna pattern doesn't
    really matter with small aperature antennas. All that's inportant is
    the forward antenna gain.

    However, transmitter power output and receiver sensitivities are NOT
    necessarily identical. Let's say you have a radical difference in
    transmitter power output between ends of the link. Since the signal
    strength the receiver displays is also a function of the other
    transmitters power output, you'll get different signal levels. This
    may be your problem.

    However, unless you have something broken, the typical transmit signal
    levels and receiver sensitivities are not sufficiently different to
    have one end enormously different from the other. Perhaps with a
    tower mounted power amplifier, but not with conventional radios.
    Methinks something is broken.

    The problem is that there's no way to tell which end is the problem.
    That's were a 3rd radio is necessary for troubleshooting. Use this
    3rd radio (preferably a laptop running Netstumbler) to connect to each
    end, one at a time. By process of elimination, either the
    transmitter, or the other receiver, on the comatose link path, with be
    the culprit.

    >There are some tall trees to the immediate right of the line but I can see
    >the antenna clearly. I've read a little about the "Fersnal zone" and that
    >you shouldn't point the antennas directly at each other. Could this be
    >causing dramas?

    It's Fresnel zone diffraction. For 800 meters range and 2.4Ghz, the
    Fresnel zone is 5 meters radius at midpoint. If you have a clear line
    of sight with a 10 meter diameter midpoint clearance, you should be
    fine. If the tree is closer to one end, you'll need less clearance.
    The Fresnel zone is also symmetrical, so that would not cause the
    symmetry problem you're having.
    http://gbppr.dyndns.org:8080/fresnel.main.cgi


    --
    Jeff Liebermann jeffl@comix.santa-cruz.ca.us
    150 Felker St #D http://www.LearnByDestroying.com
    Santa Cruz CA 95060 AE6KS 831-336-2558
  2. Archived from groups: alt.internet.wireless (More info?)

    "Jeff Liebermann" <jeffl@comix.santa-cruz.ca.us> wrote in message
    news:cg53i090944k1n7h3p6mooot0memockfs5@4ax.com...
    > On Tue, 17 Aug 2004 09:37:02 +0800, "Amhir Sohail"
    > <amhirsohail@yahoo.com.au> wrote:

    > Ok, something is wrong. If you move closer with the hardware, can the
    > access point eventually pickup the signal? Just checking if things
    > are properly configured.

    When I had both units in the same house they connected instantly with no
    configuration.

    Last night I swapped the access point (DLink 2100ap) and netcard (Netgear
    WG311) around and I still got a 40% signal going the other way. I'm guessing
    that rules out transmit and sensitivity issues?

    The cable run to the netgear was pretty long (and I was using RG58 for half
    of it) so I've ordered another 2100ap and I'll try bridge mode using Cat5 to
    make most of the run to the PC.
    I do have a laptop so I'll get netstumbler. How far does the signal spread?
    Am I likely to see it from the ground if both antennas are pointing at each
    other on roofs?

    Trees are closer one end so maybe it will infract a little on the signal. Do
    you think 40% signal is suffcient to get a connection?

    Thanks for your response

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

    "Amhir Sohail" <amhirsohail@yahoo.com.au> wrote in message
    news:4122d32e$0$27241$61ce578d@news.syd.swiftdsl.com.au...
    > Well that's strange then, for the 2 hours I was mucking around with this
    > last night that signal strength never went below 40% and never lost
    > connection.
    >
    > I'll try with the bridge connection tonight and let the group know.
    >
    > Thanks
    > Jac

    I bought another Dwl-2100AP and tried in bridge mode last ngiht. Couldn't
    get it working so I'll get up and adjust my antenna on my roof.

    I do have a complaint about the Dlink 2100AP though. There is no site
    survey! I couldn't check signal strength to verify I still had some
    connection..

    I really need an external antenna connection on the laptop to hook straight
    into the antennas to aim. I'll have to make do with using netstumbler from a
    halfway point and doign it that way. I'll update later

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

    "Amhir Sohail" <amhirsohail@yahoo.com.au> wrote in message
    news:4123fcc4$0$27219$61ce578d@news.syd.swiftdsl.com.au...

    > I really need an external antenna connection on the laptop to hook
    straight
    > into the antennas to aim. I'll have to make do with using netstumbler from
    a
    > halfway point and doign it that way. I'll update later
    >
    > Jac

    I've tested the link using netstumbler, with the two parabolic dishes over
    800 metre I'm getting an RSSI figure of around 20-24. Is this a percentage
    value? The light is green in netsumbler so I guess that means that its
    enough signal. It does go grey every so often (10 secs or so)which seams to
    be a loss of signal. Is this normal or is my link still flakey?

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

    "Jac" <amhirsohail@yahoo.com.au> wrote in message
    news:4128803e$0$27219$61ce578d@news.syd.swiftdsl.com.au...
    >
    > "Amhir Sohail" <amhirsohail@yahoo.com.au> wrote in message
    > news:4123fcc4$0$27219$61ce578d@news.syd.swiftdsl.com.au...

    > I've tested the link using netstumbler, with the two parabolic dishes over
    > 800 metre I'm getting an RSSI figure of around 20-24. Is this a percentage
    > value? The light is green in netsumbler so I guess that means that its
    > enough signal. It does go grey every so often (10 secs or so)which seams
    to
    > be a loss of signal. Is this normal or is my link still flakey?
    >
    > Thanks
    > Jac

    I've just hook my laptop up next to my pc and run netstumbler again. I get
    the greyed connection every so often to I guess thats not an issue with my
    main link. The RSSI is on about 50 and 60 seems to be the max. I guess 20
    RSSI is a little low then. Signal strenth as measured by the netgear
    software however is generally around 50%.

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

    Ok, the problem was the antenna setting on the Dlink 2100AP access point. It
    was set to "best" as soon as I changed it to "1" which I assume is external
    antenna I had immediate connection.

    Thanks for your help on this one Jeff

    Jac


    >
    > I have an 18db parabolic antenna pointed at a Tin Cantenna about 800
    metres
    > away line of sight.
    >
    > From the netcard at the cantenna side, I'm getting 40% signal strength. My
    > access point rarely sees the cantenna however and generally not for very
    > long.
    >
    > I've heard the antenna gain is same for send and receive so I take it that
    > my home made cantenna should be sending something out. Could it be that
    the
    > parabolic antenna sends in a wider arc which the cantenna can see but not
    > vice versa?
    >
    > There are some tall trees to the immediate right of the line but I can see
    > the antenna clearly. I've read a little about the "Fersnal zone" and that
    > you shouldn't point the antennas directly at each other. Could this be
    > causing dramas?
    >
    > Thanks for any input.
    >
    > Jac
    >
    >
    >
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