wi-spy followup

Discussion in 'Wireless Internet' started by danr_18, Mar 23, 2006.

  1. danr_18

    danr_18 Guest

    Now that it has been a few months, how have people found the WI-SPY to
    be?

    I emailed the WIFI folks regarding the external antenna version - here
    is their reply:

    "We are hoping to have the external antenna version available in 3-4
    months; it will have an SMA (or reverse SMA) connector.

    We will most likely ship with a small SMA antenna so that Wi-Spy can be
    used out of the box, but users are welcome to attach any antenna to the
    Wi-Spy (for directionality, gain, etc).

    Due to changes in the plastics and higher manufacturing cost this
    version will likely sell for [for somewhat more money -- they aren't
    100% sure of the price, so I'm not posting their proposed price, as per
    their request].

    If you need the directionality of the external antenna I would suggest
    waiting, otherwise the current version is fine for troubleshooting
    wifi."
     
    danr_18, Mar 23, 2006
    #1
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  2. hath wroth:
    Or, you can build one of these:
    http://802.11junk.com/jeffl/antennas/Salad-Dish/index.html
    It works with any USB dongle wireless device. Not much gain (I
    haven't measured it) and fairly directional. Good enough for
    sniffing.
     
    Jeff Liebermann, Mar 23, 2006
    #2
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  3. danr_18

    danr_18 Guest

    Cool...

    Any directions or at least the name and size of the parts?

    Does this connect or is it held over the dongle?
    If the latter, how do you manage to balance everything while walking
    around?
     
    danr_18, Mar 23, 2006
    #3
  4. danr_18

    Chuck Olson Guest

    I went to the hardware store and got the fittings per Jeff's photo, but I
    found an old beat-up photoflood reflector at a flea market that looked
    closer to a parabola (if you ignore the dents), and that seems to work okay.
    The fittings are nice in that they can go into a lot of different reflector
    types.

    I don't know if Wi-Spy people will read this, but I did notice a couple of
    things they could do better with the software. You can put the cursor on any
    of the three traces, but the dB readout on that cursor still bounces around
    with the instantaneous trace - - it would be better if it followed the
    actual trace the cursor was assigned to. The auto-scaling of the average
    trace is nice, but why can't there be something that tells what the new
    scaling is? - - dB per division, maybe. If the peak trace goes to flat top
    limiting, is the electrical peak truly limited, or is it just the display
    that limits. If the electrical peak isn't limited, then perhaps the average
    trace is still valid through what looks like overload signals. For judging
    antenna performance differences, the average trace would seem to be more
    meaningful. I set a D-Link router to a beacon interval of 3 milliseconds to
    increase the average energy readout in an antenna study, and the average
    trace became quite useable. But when I went to beaconing at 1 millisecond
    intervals, I think the transmitter overheated, judging by the way it lost
    symmetry in the channel it was assigned to.

    I find the device to be quite useful, and with further enhancements it will
    really be a valuable item for antenna, router and bridge optimization and
    troubleshooting - - looking forward to whatever they can come up with.

    Chuck W6PKP
     
    Chuck Olson, Mar 24, 2006
    #4
  5. Well, it's a stainless steel salad bowl I picked up at the hardware
    store for about $8. Unfortunately, I drilled through the bar code
    label. I recall that it was made in India. It's NOT a parabola and
    could easily be improved. Meanwhile, search Google for "stainless
    mixing bowl" and you'll find a collection of possible bowls. Try to
    get one with a flat bottom as they're easier to drill and punch.

    See:
    | http://groups.google.com/group/alt....ternet.wireless&rnum=1&hl=en#35a34f5ca82b2ef4
    thread for some discussion on the design. Bashing the 1 3/8" D hole
    should be done with a chassis punch and NOT a circular hole saw, which
    makes a mess.

    If you don't wanna deal with the mixing bowl, then a flat plate or
    corner reflector will work. Make the flat part 1/2 wave diameter, and
    bend the edges up to form the corner reflector. Sorta looks like a
    parabola but it's really a corner reflector. Kinda like a solar
    cooker reflector.
    You shove the dongle into the 1" PVC pipe with a USB extension cable.
    It takes some effort to find the optimum focal point. The nice part
    is that it requires no modifications to the dongle.

    One change I wanna try is to through drill the two PVC electrical
    joints so that the 1" pipe can be shoved all the way through them in
    one piece. I'm digging through a large pile of ancient end mills as
    we speak but managed to cut my fingers. Oops.
    Balance? It hardly weighs anything. Not a problem. Use your
    imagination for the back piece of 1" PVC. You could install a PVC "T"
    connection, which would form a pistol grip handle. Drill it for a
    1/4-20 bolt and mount it to a tripod. Be creative.

    One of my non-geek friends saw the salad bowl antenna in my truck and
    commented that it was nice that I was building a bird bath or
    fountain. Sigh.
     
    Jeff Liebermann, Mar 24, 2006
    #5
  6. danr_18

    danr_18 Guest

    Chuck -

    Why don't you email your software suggestions to the Wi-Spy people --
    or post on THEIR forum?
    Then you'd be sure that they could see them.
     
    danr_18, Mar 24, 2006
    #6
  7. danr_18

    danr_18 Guest

    Thanks....

    Hmmm, chassis punches seem to be about $50... A bit steep for one time
    use
    (especially considering Wi-Spy will be updated shortly).
    I'll ask some handy neighbors, but I doubt they'll have one either.
     
    danr_18, Mar 24, 2006
    #7
  8. danr_18

    Chuck Olson Guest

    The Greenlee punch isn't that rare - - any electrician would have a set of
    conduit punches including the one for the 1" fittings that Jeff showed in
    the picture. I don't think I paid more than $40 for my set of 4 Greenlee
    punches at the flea market. The 1" punch is also stamped 34.6mm and I
    measured mine at 34.5mm, so that's pretty close to the actual hole size.
    Ebay looks like a good source for the 7235BB 1/2" to 1 1/4" set.

    Another way to make this hole would be to use a nibbler. I think Radio Shack
    sells a nibbler of sorts, and there is also the venerable Adel Nibbler that
    has been around for ages, but the price has ballooned with all the
    inflation. I also found an excellent compound tin snips that cuts left, made
    by Midwest in USA (Wiss is not as good), and this would do the job, too. The
    final method, and the least desirable due to all the work involved is to
    drill a bunch of holes with very little metal between them in a circle, and
    then snip through the separating metal with diagonal cutters, and file the
    rough edges smooth.

    Chuck
     
    Chuck Olson, Mar 24, 2006
    #8
  9. 34+ mm????? I sure hope you read that wrong. 1" = 25.4mm. I can
    understand a little bit of difference, especially since US/Imperial
    measures tend to be "nominal", but a 30% error seems extreme.
     
    Derek Broughton, Mar 24, 2006
    #9
  10. danr_18

    Chuck Olson Guest

    I agree, the size labels for conduit and fittings are pretty far from their
    actual size.
     
    Chuck Olson, Mar 24, 2006
    #10
  11. danr_18

    dold Guest

    One inch would be the internal diameter of the PVC. This is fairly hefty
    stuff. 1" sched 40 PVC for water is 1-1/4" outer diameter. That's the
    hole you would be drilling.

    If you don't have a chassis punch, you should be able to drill through the
    bottom by nailing it to a piece of scrap wood, and drill it with a hole
    saw. Two nails or drywall screws at 1" spacing, drill bit centered between
    them... I think that would be okay, but Jeff's the one who has experience
    in mangling a bowl. I've drilled through some sheet metal successfully,
    drilling into backing wood. The bowl makes it a little more interesting.

    The alternative would be a flange instead of the feedthrough coupling, and
    a much smaller hole, just for the cable. The bolts to secure the flange
    could bolt to something on the back side that provided a handle.
     
    dold, Mar 24, 2006
    #11
  12. One inch would be the internal diameter of the PVC. This is fairly hefty
    stuff. 1" sched 40 PVC for water is 1-1/4" outer diameter. That's the
    hole you would be drilling.[/QUOTE]

    I found that 1 1/4 was a bit tight. It would work, but the PVC parts
    ended up a bit tilted as the stainless shredded the plastic thread. I
    also wanted a little bit of slop to compensate for centering
    inaccuracy. Methinks 1 3/8 is the correct punch size.

    Just a reminder... use the electrical gray PVC fittings and NOT the
    white plumbing PVC fittings. The electrical type are straight thread,
    while the plumbing are tapered. The electrical goes together and
    comes apart quite easily. The white plumbing type are very difficult
    to manage.
    You proceedure works just fine with a drill press. However, the bowl
    was far too large to fit in my cheapo junk drill press. So, I tried
    it using a hand drill and eended up with a mess. It might work with a
    hole saw and a block of wood in a drill press, but I haver wast able
    to try it.
    The cable will fit through a smaller hole but the typical USB
    connector will not. The USB connectors are permanately attached to
    the cable and cannot easily be removed without cutting the cable and
    then splicing it back together.
    I found the UPC bar code on the salad bowl
    "Item #108"
    21614-00071
    Made in India
    I haven't tracked down the manufacturer yet.
     
    Jeff Liebermann, Mar 25, 2006
    #12
  13. Jeff Liebermann, Mar 25, 2006
    #13
  14. danr_18

    danr_18 Guest

    danr_18, Mar 26, 2006
    #14
  15. Jeff Liebermann, Mar 27, 2006
    #15
  16. danr_18

    danr_18 Guest


    If I look around local stores -- what are some things to look out for?

    I guess as close to parabolic as possible? Size between X and Y?
    I see on that other website, alot of mesh or metal strip like bowls --
    which makes it easier to create something without drilling... how
    useful are those?

    Thanks
     
    danr_18, Mar 28, 2006
    #16
  17. Avoid salad bowls with almost vertical sides. Vertical sides don't
    contribute any gain. It should resemble a parabola.

    There's 2 ways to use a wok (shallow parabola). One is as a parabolic
    reflector which will have a focus quite far from the dish. The other
    is just as a flat plate reflector, where the USB dongle antenna is
    about 1/4 wavelength from the reflector. At that point, you might as
    well use something flat, like a pizza dish. The gain is about the
    same.
    Nope. The bigger the dish, the higher the gain. Try not to get
    rediculously big. Also, materials are an issue. Copper, stainless,
    and aluminum are good. Steel, galvanized, and anodized are not so
    good.
    They work. Look at it this way. ANY antenna is better than the
    circuit board antenna found in the typical USB dongle. If you don't
    wanna drill, a pie plate will do. The results won't be optimum and a
    proper design will yield more gain, but that requires drilling,
    calculating, measuring, and some effort.

    I did some dish calcs here:
    | http://groups.google.com/group/alt.internet.wireless/msg/866cc5bdeab8a464

    Argh. Do something, even if it's wrong.
     
    Jeff Liebermann, Mar 28, 2006
    #17
  18. danr_18

    Chuck Olson Guest

    Gentlemen,

    I noticed that there is now an upgrade for the software that runs the Wi-Spy
    dongle - - latest version is 2006.3.17.0. There is no obvious mention of the
    reason for the upgrade in the User's Guide, but maybe something was changed
    through the uninstall-install process. I haven't checked the Metageek FAQ
    lately.

    I've been checking the dB calibration of the display with an attenuator set
    that's good to about 4 GHz, and find, as I suspected, the numbers are almost
    meaningless. For display levels above -47 dB, there is a consistent 1.5 dB
    change for every 1 dB difference in the Wi-Spy display. Below -47 dB, the
    actual change runs about 3 dB for every 1 db difference in the Wi-Spy
    display. This information might come in handy when comparing antennas on an
    Access Point with a Wi-Spy receiver. Using a 1.2" whip on an N connector as
    a reference, I found a Biquad antenna gives about 9 dB gain, while a
    "Cantenna" made with 2 large "Bush's Beans" cans and a 4" to 6" heating duct
    adapter gives about 12 - 15 dB gain. We also built some Helix antennas on
    42mm and 33mm forms, both about 16" long, and found them only about 3 dB
    better than the 1/4-wave whip! The polarization loss doesn't help, I guess.
    So your recommendation, Jeff, to put up a Biquad is very good advice. The
    Can-with-horn performance was a surprise, and coupled with its greater
    directivity and lower sensitivity to off-axis sources for lower
    interference and noise, it might be good for critical situations, but it's
    larger and more wind-prone, so it's not so easy to apply. I made a cradle
    out of some plywood and a couple of strips of angle aluminum, all held to
    the "Cantenna" with stainless hose clamps. The plywood then can be U-bolted
    to a mast.

    Has anyone attempted to install an antenna connector on his Wi-Spy? You know
    these units without a connector won't be worth much after the "connectored"
    product arrives, so maybe it's worth the effort to tear into the ones we
    have and put on-line a few photographs and a mod procedure.

    Good luck to all,

    Chuck

     
    Chuck Olson, Apr 1, 2006
    #18
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