WRT54G and 20 dbi yagi

Discussion in 'Wireless Internet' started by purple, Jan 21, 2005.

  1. purple

    purple Guest

    im trying to reach the ap that 5 kilometers far from me...i have wrt54
    in client mode attached to the roof with weatherproof box and i can se
    the ap...has anyone suggest antenna??...im planning to buy 20 db
    planet yagi..
     
    purple, Jan 21, 2005
    #1
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  2. purple

    Peter Pan Guest

    Depends on where you are (what the weather is around there, and what it may
    do to signal strength). For long links, I've gone highly directional yagis,
    but only in places that don't have much bad weather. For those I do a combo
    of increasing the signal strengh, and yagi's (but not quite as strong
    needed).

    for that specific device (wrt54g), check out the firmware upgrade from
    SveaSoft at - http://www.sveasoft.com
    Stock power is 28mw, but the Svea firmware will let you boost that up to
    251mw. The higher power goes thru stuff like fog/rain/snow etc, better than
    a longer antenna, and costs about the same (ie firmware upgrade costs about
    the same as a more powerful antenna).

    There are also "booster/repeater/amps" (like the cell phone repeaters)...
    Connect to the back of the AP, and give large amounts of output power
    (100mw - 3w) for a very tight beam (they may be technically illegal,
    depending on the power output, and your country/location), I'm just
    mentioning that it is "theoretically" possible if someone wanted to do it)
     
    Peter Pan, Jan 21, 2005
    #2
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  3. Ummm... I beg to differ. Last time I checked, dB's of antenna gain
    are the same as dB's of power gain. Going from 28mw to 251mw is a
    9.5dB increase. That's better than an 8dBi single patch antenna, but
    not as good as panels or dishes that go up to about 24dBi gain.

    In addition, cranking up the tx power only increases the gain in one
    direction. If you're talking to an identical high power unit in a
    point to point bridge arrangement, increased tx power is a good idea.
    However, if you're setting up an access point, and talking to the
    typical +15dBm (32mw) laptop client, all the tx power in the world
    isn't going to improve communications if the access point can't hear
    the laptop clients. (This is why I detest high power radios used in
    mesh networks). On the other foot, an increase in antenna gain
    improves the situation in both transmit and receive.

    Incidentally, the maximum legal tx power in the US is 1 watt (+30dBm)
    into a +6dBi antenna. It's not terribly clear in 15.247, but that
    means 1 watt no matter what type of antenna or service you're using.

    As for higher tx power going through fog/rain/snow better than a
    longer antenna, methinks you're correct for only a limited subset of
    conditions. Fog/rain/snow/ice/bird_dropping will detune an antenna.
    Water incursion into the antenna or coax will cause signal loss. In
    general, the simpler antennas tend to be less sensitive to water
    related problems than the more complex high gain antennas.
     
    Jeff Liebermann, Jan 21, 2005
    #3
  4. purple

    Peter Pan Guest

    While that is true in ideal conditions, one of the first q's I asked was
    where he was. For instance, in the Pacific Northwest with lot's of precip,
    bumping up the power seems to work better (along with a moderate antenna),
    but in the deserts of nevada, you don't get a lot of rain to scatter the
    signal, and it doesn't really matter, just high gain antennas seem to work
    okay. As for his specific application, he just basically wants to bridge two
    ap's, but didn't say where he was.

    Thanks for the 1 watt power limit in the US, my supplier has a 1w/2w/3w
    802.11 repeater/boosters, good to know the 1w (for $149) is reasonable for
    use in the US, gives me an idea for bridging to a second site 10km away. Any
    info on solar powered repeaters? Seems to work for cell and amatuer radio
    stuff.
     
    Peter Pan, Jan 21, 2005
    #4
  5. In my limited experience in the deep dark wet forests of the Santa
    Cruz mountains, rain scatter is not a problem at 2.4GHz. I have links
    that I monitor continuously (using MRTG and SNMP). For quite a while,
    I was mystified by how the signal strength would not vary in the
    slightest during a big rain, but 2 days later, drop anywhere from 3 to
    10dB. It would then take a day or two to recover. No rain in sight
    meanwhile.

    Note that I said 2 days later, not the next day. It took a while to
    figure out what was happening. The rain would usually appear in the
    evenings. Everything would get soaked but would be mostly waterproof.
    The next day, the sun would appear and raise the air pressure inside
    the coax cables. At night, the temperature would drop, causing the
    air pressure inside the coax cable to drop, which would suck in a few
    drops of water through my alleged waterproof seals. This usually
    would not cause any problems until the heat of the sun caused the
    water to evaporate. High humidity water inside an air dielectric coax
    was as a good as a short circuit. Anyway, it wasn't the rain drops in
    the path that was causing the water problem. I suppose it's worse in
    the Pacific Northwest, with more fog/rain/moisture, with the added
    complication of freezing.

    Another water related headache is water condensing on circuit boards.
    When the temperature hits the dew point, everything gets soaked. The
    heat from the boards will usually prevent this problem. However,
    really low power devices don't generate enough heat to totally prevent
    condensation (or freezing). The easiest fix is to mount the boards
    vertically, so they drain. Otherwise a spray wax or urathane
    conformal coating will really help. However, that doesn't work with
    connectors that tend to trap water.

    Anyways, it's not atmospheric precipitation attentuation that causes
    problems. See bottom of:
    http://www.telex.com/Wireless/faq.nsf/C!OpenView&RestrictToCategory=Radio Propagation
    At 2.4Ghz 0.08dB/mile for a torrential rain is nothing.
    3 watts? Kinda illegal except for ham radio use.
    Yeah. I've built three solar AP's and one repeater. The first used a
    DC-DC converter to supply power from a pile of gel cells. Morningstar
    charge controller. Then I discovered that the WAP54G family will run
    on any voltage between about 4VDC and 15VDC. So, I just hung it
    across a 12V battery, charged it with another charger controller, and
    discarded the DC-DC converter. The calcs are fairly simple. Look up
    the insolation values for your area. Calculate your power drain
    requirements, which will size your battery, charge controller, and
    solar array. It's not much to see, but I can post photos when I find
    them. (Hint: if you've read my stuff, you'll probably have noticed
    that I don't think very highly of repeaters, mesh networks, and
    overpowered transmitters).
     
    Jeff Liebermann, Jan 22, 2005
    #5
  6. purple

    Peter Pan Guest

    Within most countries, it actually a boat supplier, and are *supposed* to
    only be for offshore use.

    Sounds like what I need for a client. A few people living in a valley, with
    no wifi, but they have cable internet in the town on the other side of the
    mountains. Sounds like a solar power repeater on the ridge, may be just the
    thing..
     
    Peter Pan, Jan 22, 2005
    #6
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