DIY WiFi antenna (to increase reception)

Discussion in 'Linux Networking' started by gaikokujinkyofusho, Jun 9, 2005.

  1. The statement ([1] above) is not only ridiculous,
    it would be seriously misleading to anyone not familiar with WiFi.
    I understand what you are saying.
    I'm just saying that it does not correspond to my experience.
    That just isn't true, in my experience.
    Eg I have a Sony WiFi card which does not work as well as my Orinoco cards.
    [It also needs a different driver.]

    Different APs in my college seem to have vastly different ranges.

    The Orinoco PCI-to-PCMCIA card on my desktop has an external aerial,
    and if this is removed the transmission is greatly weakened;
    so all units do _not_ have "about the same capabilities".

    A colleague in work had problems with the built-in WiFi in his laptop.
    I put in my Orinoco card, and it worked perfectly.
    I don't need to know anything in order to describe what happens.
    Maybe you would be better off if you didn't know so much about 2.4GHz waves,
    and experimented a bit more.
    That's not possible in this case;
    the wall goes from ground to roof,
    and the roofs on the different sides of the wall are different.
    Anyway the signal would have to go a vast distance
    if it had to go up to the roof and back again.

    There are doorways in the wall;
    but it would have to go along a very strange path to get through them,
    You haven't convinced me.
    I still believe that WiFi should work perfectly in any normal dwelling;
    and if it doesn't then you should try alternative devices
    before calling in the 2.4GHz experts.

    I might mention that my WiFi is too good!
    There is a firm (Intermec) in the same building
    which specialises in WiFi.
    This is separated from my part of the building by a concrete fire-wall,
    again from ground to roof.
    I was told the other day that they can pick up my WiFi loud and clear,
    and could connect to the web through my desktop.
    [For various reasons I wasn't using WEP at the time.]
    Timothy Murphy, Jun 11, 2005
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  2. This might be a sensible remark if you were talking about
    long-range WiFi transmission, but it is a ridiculous remark
    if you are talking about WiFi in a house.
    The whole point of WiFi is that it is _not_ line-of-sight.

    It's exactly on a par with telling someone
    that your "best chance" of communicating with a GSM phone
    is if you can see the network antenna.

    This is true in the sense that the chance is 100% in that case,
    while it is only 99.999% otherwise.
    Have I run into a Mafia of radio engineers?
    I'm not an engineer, but I'm reasonably au fait with Maxwell's equations,
    and have even been known to lecture on relativity.

    You don't have to know anything about hydrodynamics
    to know if there is water coming out of the tap.
    Timothy Murphy, Jun 11, 2005
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  3. That is the opinion of a person who admits to a serious lack of
    knowledge of the topic. I fail to see why you want to make
    a fool of yourself.

    Your entire article is filled with contradictions and foolishness,
    such as this comment:
    And technical fallacy, such as this:
    (There is no point in further discussion...)
    Floyd L. Davidson, Jun 11, 2005
  4. Multipath and polarization changes are essential to
    understanding propagation within a building. And 2400MHz is
    absolutely "line of sight".
    Floyd L. Davidson, Jun 11, 2005
  5. gaikokujinkyofusho

    Stan Goodman Guest

    This is the whole point?

    Please tell us what it is about WiFi that guarantees that it does not depend
    on line of sight. Your explanation may not make use of reflections, because
    reflections are how we are explaining to you why your arrangement works as
    it does.

    I will try again. When you find that you can communicate without a line of
    sight, the explanation is that you have been fortunate in that there is a
    sufficiently strong reflected path; if you want to remove the element of
    fortune, you will arrange a line of site, else you will take potluck. If you
    find that rotating the polarization place of the receiving antenna produces
    no great change in signal strength, the explanation is that the environment
    has produced many reflections, each with an associated rotation that you get
    a passable signal at any angle. Again, fortune has smiled upon you, which it
    didn't have to do; you could remove the element of luck by providing a line
    of sight. If, fortuitously, you get an acceptable signal without a line of
    site, you are golden -- but it is foolish to try to make a physical
    principal of your good luck, which is the way that many people go broke at
    that track. This is exactly what Floyd has been trying to tell you. I don't
    know where he gets the patience to keep trying.
    Notice the key phrase: "Best Chance". This doesn't mean that one way it will
    work and the other it won't. Look up each of the two words in a dictionary.
    You have, of course, sucked these number out of your thumb. Leaving aside
    the effort to qunatify the unquantifiable (because we don't know what a
    standard house is like), one way is better than the other. If the
    "otherwise" is satisfactory, buy yourself a beer and pat yourself on the
    back for having bought a house with sufficiently messy propagation
    properties to have made it turn out that way.
    Oddly, I had the impression that we had run into a know-nothing. I have no
    clue what it is that you are arguing about, or why.
    I don't think that we have touched on Maxwell's equations, or even on "au
    fait". Certainly not on relativistic effects. Bear in mind that people go to
    school to learn this material, which is not always intuitive
    I think the usual formulation is that you don't have to be able to lay eggs
    in order to know how to identify a bad one. Equally irrelevant.

    As I understand it, the "water coming out of the tap" in this case is the
    fact that you can get usable signals even without a line of sight, even
    through two-foot-thick dungeon walls (if you live in a two-dimensional
    world). The analogue of "a knowledge of hydrodynamics" in your example would
    be a knowledge of electromagnetic propagation, which would explain to you,
    as Floyd has tried vainly to do, WHY the observed facts seem to contradict
    the requirement for a line of sight.

    Lacking as I do the infinite patience that I might have if I, like Floyd,
    had to sit through long Arctic winter evenings, I am out of this thread.
    Stan Goodman, Jun 11, 2005
  6. gaikokujinkyofusho

    YouCanToo Guest

    A little feedback to be had
    YouCanToo, Jun 11, 2005
  7. gaikokujinkyofusho

    Unruh Guest

    Uh, no. for someone who claims to know something about electromagnetic
    propagation to claim that the absorption of material at 2.4GHz and optical
    frequencies are the same is sad. And even if it meant "line of sight if all
    absorbers were removed" is wrong as has been emphasised in the discussions
    about reflections. Ie it is NOT "line of sight" except as a crude
    Unruh, Jun 11, 2005
  8. gaikokujinkyofusho

    YouCanToo Guest

    Your statement is *WRONG* the band that WIFI is in (2.4Ghz) is indeed
    LOS. It would seem that perhaps you need to learn a bit more about RF
    YouCanToo, Jun 11, 2005
  9. gaikokujinkyofusho

    YouCanToo Guest

    he should perhaps think of the 2.4Ghz range as acting like a light beam.
    Perhaps he will get the Idea of what LOS means.
    YouCanToo, Jun 11, 2005
  10. gaikokujinkyofusho

    YouCanToo Guest

    Actually the term should be reflection instead of absorption.

    And even if it meant "line of sight if all
    There is nothing "CRUDE" in the explantion that the WIFI (2.4Ghz) is
    Line of Sight. Plain and simple (the 2.4Ghz) band is LOS. if I remember
    right from school the 2.4Ghz band (SHF) is at the low end of infra-red
    light. And as we all should know that "light" is "line of Sight"
    YouCanToo, Jun 11, 2005
  11. gaikokujinkyofusho

    Unruh Guest

    Except it is not. A light beam is stopped by a piece of paper, 2.4GHz is
    not. 2.4G is stopped by aluminium screen. a light beam is not.
    If you mean 2.4GHz has a tought time bending around absorbers, just as
    light does, then you are right. (ie placing a square meter aluminium screen in front of
    your antenna will do no good to reception, while it would do nothing to
    your AM radio reception.) But that is NOT the question here. The
    question he raised was the use of such receivers in the home hidden behind
    walls or under floors or behind two foot thick granite walls.
    And he is perfectly correct that although such
    materials present insuperable obstacles to light, they may well present
    very little obstacle to 2.4GHz radio.
    Thus talking about "line of sight" is silly, especially since as you have
    pointed out, reflections abound in the radio whereas they do not in the

    To find out if a certain material is transparent to radio waves, "line of
    sight" is a useless mantra. "Try it and see" is a much better one. Of
    course there are rules of thumb. Do not try it through wire mesh covered
    walls-- eg do not enclose your access point in a wire cage to protect it
    from the rats. But if you are in a house, try it is still the best advice,
    since you almost never actually know what the microwave transparency is of
    all the material in the walls/floors etc. Nor do you in general know what
    their reflectivity is.
    Unruh, Jun 11, 2005
  12. gaikokujinkyofusho

    Postmaster Guest

    Wow... so many replies, rat hole-ing, theory, conjecture,
    polarization, reflection, absorption, arguing, wondering into
    relativistic space-time and expressions of disagreement and
    frustration... whoa... IMHO, the only Maxwell's you might need is
    the one with coffee in the can.

    In the amount of time that has been spent, one could have
    easily constructed the tinfoil parabola and given it a whirl.
    We're talking tinfoil, a 9 inch piece of cardboard, and
    5 minutes to construct the entire device. If this device
    doesn't work out, due to physical constraints of the embedded
    WiFi in the notebook, let me know and I'll cough up a design
    with longer focal point, or one that uses a passive 2D reflector.

    I thought the original poster was looking for a solution,
    not a discussion in electrodynamics, T and M field theory :)

    Back to solving the problem....
    ----- Original proposed solution ---

    You'll need a 9 inch piece of cardboard,
    and some aluminum foil. Then create a parabola

    Be sure that the focal point is ~ 2.267 inches from the nearest
    point on the parabola. Now cover your cardboard with the foil,
    and bend into the parabola that you just drew. Put the wireless
    antenna at 'F' ( the focal point ) and point this at the nearest
    access point. You got it...

    Note: You can create two parabola shapes out of a piece
    of cardboard, and bend the aluminum foil/cardboard around
    these two pieces. Then glue, to hold it in place.


    Note: If you use two cardboard cutouts, and bend the foil/cardboard
    around them, then, one can punch a hole in these to cutouts, at
    the focal point, and slide the mechanism down over the
    antenna of an access point. Thus creating a directional access
    point with lobe that is directional with a longer range in that
    direction :) Handy for hopping between buildings :)

    Postmaster, Jun 11, 2005
  13. gaikokujinkyofusho

    YouCanToo Guest

    You are mixing apples and oranges here. It has to do with the wave
    length of the signal. The same reason that you can see food cooking
    inside you microwave, but the microwaves do not come thru the door.
    The term is reflector not absorbers

    just as
    Different wavelengths

    But that is NOT the question here. The
    Wrong here. What he is encountering is a bounce of the signal or better
    called a reflection.
    perhaps a visit to can clear up some of your
    YouCanToo, Jun 11, 2005
  14. gaikokujinkyofusho

    YouCanToo Guest

    As per a quick google

    In a typical wireless environment, no direct line-of-sight (LOS) path
    between the transmitter and the receiver exists. In fact, the
    electromagnetic waves emitted by the transmitter usually take different
    paths to get to the receiver, depending upon the obstacles in the
    environment. As a result, the received signal comprises a sum of the
    various contributions, each of which differs in both amplitude and
    phase. In many cases, the signals combine in a destructive manner,
    thereby severely degrading the signal's strength. The receiver faces the
    difficult task of properly demodulating and decoding the signal into
    something that resembles the original. Despite the emerging receiver
    technologies multipath problems can still seriously inhibit a wireless
    system's performance.

    Can you argue with that :)
    YouCanToo, Jun 11, 2005
  15. gaikokujinkyofusho

    James Knott Guest

    Actually, you're off by about 5 orders of magnitude. The low end of the IR
    spectrum is about 100 microns or micrometres. A 3 GHz microwave signal has
    a wavelength of 10 centimetres ore 10,000,000 microns.
    James Knott, Jun 11, 2005
  16. gaikokujinkyofusho

    James Knott Guest

    Well, lessee now. Right now, I'm using WiFi as I type this note, while
    sitting out on my balcony. There are a couple of walls between me and my
    access point. There is no free air path between my computer and access
    point, no matter how many reflections there are. Therefore, my signal is
    passing through walls. Also, in general in radio, line of sight doesn't
    necessarily mean optical line of sight. As long as there's nothing in the
    path that blocks the signal, you've got "line of sight". Common building
    materials, such as wood, brick and drywall are relatively transparent to
    RF. Metal is not. As another example, I offer my car's remote control
    lock. Even when in my unit or in the stair well, I can operate the car
    locks or honk the horn, even though the signal has to pass through concrete
    in either situation.
    James Knott, Jun 11, 2005
  17. gaikokujinkyofusho

    James Knott Guest

    No, it's the delay involved in converting the speech into the packets which
    are transmitted and then back into continuous audio. When you are in the
    same room, you hear the original speech, direct via the air and a fraction
    of a second later, the same words coming in through the phone. It confuses
    your brain and makes it hard to understand what's being said. You don't
    get the same effect with analog cell phones, but you will with voice over
    James Knott, Jun 11, 2005
  18. So, you can't read English (in addition to not having an
    understanding of microwave propagation either). I'm sorry,
    perhaps you actually can read something other than English?

    However, if you will, please note in the text you quoted above
    the two quote marks around the words "line of sight". What you
    need to know is that such syntax means that your comment is
    nonsense. You cannot draw the conclusions you did about what it
    implies, given what it says. The error is yours, not mine.

    The rest of your article divorces my entire discussion from the
    one sentence that you misread, and assumes that what you
    misunderstand trumps the entire rest of my comments. I can't
    imagine a rational person making such an analysis, whether they
    understand English or not.
    Specifically, that was emphasized by *my* discussions about
    reflections. Did you miss that too? The discrepancy should
    have given you a clue that you weren't understanding something.
    No. It is "line of sight", period. What you are missing is the
    concept of exactly which points must be line of sight. Oddly
    enough, before I posted the previous article, I wrote an
    explanation of this, but edited it out because it is just to
    complex and confusing for the level of understanding being
    addressed (i.e., it would add nothing for Timothy, and only
    distract from more essential basics).

    The "Line of Sight" requirement is, at 2400 MHz, almost exact.
    Obviously 2400 MHz signals go through dry wood or paper, so it
    is not an exact correlation. But I don't think that is what you
    are missing, as I've discussed that previously.

    The two points between which "line of sight" must exist are
    *not* the transmitting and receiving antennas. Rather they are
    between each pair of interacting antennas within the entire
    path. That means, for example, between a transmitting antenna
    and a passive reflector, between any two passive reflectors, or
    between any passive reflector and an active receiver. If two
    antennas don't have "line of sight", they don't interact, and no
    path exists. If the do, they interact and there is a path.

    The very term "multipath" indicates that we are not discussing
    the aggregate signal going from a transmitting antenna to a
    receiving antenna as if it is one thing, but rather that we are
    analyzing its component parts. While "multipath" specifically
    references multiple component parts arriving at a single
    antenna, it also certainly implies that each of those
    component parts might also have multiple segments.

    Anyone who has even a modicum of experience with path
    engineering is aware of the specific meaning of "line of sight"
    as it applies to various different frequency ranges. It is a
    mark of overall ignorance coupled with a few poorly understood
    facts to come off with your trivially incorrect comments.
    Ignorance is fine though.

    But your attitude sucks, and coupled with ignorance is hilarious.
    Floyd L. Davidson, Jun 11, 2005
  19. We've got a couple of people here who will try, simply because
    neither of them will take the time to understand it.

    Both are familiar with terminology used by a carpenter, and
    want to apply it to microwave path engineering. With hilarious
    resulting statements of "fact".
    Floyd L. Davidson, Jun 11, 2005
  20. gaikokujinkyofusho

    Stan Goodman Guest

    What sort of house do you live in? Mine is a single storey structure made of
    concrete blocks, with a metal-screen lathe and plaster ceiling under a tile
    roof. Is yours like that? Or is it a frame structure? These walls are made
    of what? Gypsum board? That would sound to me like not much of a block to
    the passage of a signal at these wavelengths; it would sound like they are
    fairly transparent. "Transparent" means they don't exist, from the point of
    view of line of sight. The fact that, not having been born on the planet
    Krypton, you can't see them doesn't change that.

    If the walls are concrete, and the signal "passes through them" as you say,
    then by definition they are transparent, and the same reasoning applies. Are
    they two feet thick?

    Anything that the signal "passes through", to repeat, is transparent, and
    meaningless for line of sight. Line of sight doesn't require "free air". If
    that were not true, your glass or plastic spectacles would be interfering
    with the line of sight to your breakfast coffee and the newspaper.
    Stan Goodman, Jun 11, 2005
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