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Multipath WLAN problem?

Discussion in 'Electronic Design' started by Joerg, Feb 19, 2009.

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  1. Joerg

    Joerg Guest

    Hello Newsgroup,

    After moving the office one of the things that doesn't work reliably
    anymore (besides a dead printer and a dead Tektronix) is the WLAN. It's
    a Linksys BEFW11S4 router with the routing parts disabled, to act only
    as a wireless AP. Worked well for all those years.

    Long story short I can achieve good to excellent signal strength in the
    living area. However, while the connection via this WLAN point always
    works just fine in the office it is very erratic in the living area of
    the house. Frequent Internet access time-outs despite great signal
    strength. We have insulation in all exterior and interior walls,
    unfortunately aluminum backed.

    Tried a parabolic reflector on one of the diversity antennas. Even more
    signal, but same problem. Can't put it on both because that kills access
    to part of the office. Any ideas?
  2. Joerg wrote:

    1. Could be configuration problem. Check the box "reconnect
    automatically" in the wireless network setup. Disable Wireless-N, stick
    with wireless-G.

    2. Interferrence with some other equipment at 2.4GHz. Cordless phones,
    wireless headsets, etc.

    Vladimir Vassilevsky
    DSP and Mixed Signal Design Consultant
  3. Joerg

    Joerg Guest

    Yep, 121.6V, quite sinusoidal, plus it's all protected.
  4. Joerg

    Joerg Guest

    It's very difficult to access this router because it sits behind another
    router. So dynamic IP :-(

    Anyhow, it doesn't offer much in terms of settings, basically you can
    select whether you want to use only one antenna or do diversity on both
    (which I have to). It works fine everywhere except in the living space
    where the signal has to cross two walls with aluminum-foil fiber
    insulation in them.

    That's what I had scoped out really well when installing it. Channel 2
    was best and still is, nothing else going on on this channel.
  5. Joerg

    Joerg Guest

    It's planned. That area is the only one where I hadn't strung CAT-5 yet.
    Made myself an access hole last year so now I can get there. But not
    before spring, right now it's ugly down there. But: I want to be able to
    just schlepp the little netbook to the living quarters so my layouter
    can ping me with a new round of Gerbers when he does one of those urgent

    Yep, just like this dreaded ATSC we'll get in June :-(

    I wish WLAN had an option in the protocol where you could set it to 300k
    or so in order to ruggedize a connection. But it's always full bore.
  6. Joerg

    Joerg Guest

    Well, the Brother MFC printer isn't intermittent. Other than a backlit
    LCD it's dead as a door knob. The Tektronix only emits intermittent
    hissing sounds.
  7. Joerg

    Joerg Guest

    Noise on channel 2 is quite low.

    That's what I am afraid is taking place :-(

    The strange thing is that while it works it does so at top speed. When
    it quits it's totally dead for many seconds until it catches again.

    Yes, but probably would require also upgrading some of the computers but
    is an option. One problem is that "modern" computers are dumbed down.
    All the "diagnostics" you get is five bars. No dBm levels, packet
    statistics and such, much better in the good old days. OTOH it's even
    worse with "modern" TV sets. All the diagnstics you get there is a
    picture or a blue screen.

    The 2nd AP may actually be a great idea. Thanks. Only thing is that the
    'puters would have to be trained to switch when packet losses mount.
    Which is probably something a "modern" OS cannot deliver.
  8. Baron

    Baron Guest

    Double NATing ?
  9. Joerg

    Joerg Guest

    Did you check the full width of this channel? 802.11b channels
    overlap, a lot. Channel 2 would conflict with anything on Channel 1
    (or with devices below that frequency by several MHz) and with
    anything on channels 3 through 6.

    Well, there is something (weak) operating on Ch1, and stuff on Ch6. Not
    much choice. Unless I'd pull the main breaker on some neighbor's houses ;-)

    Same scenario as years ago and Ch2 turned out to provide the best SNR.
  10. Joerg

    Joerg Guest

    Essentially the router part is disabled. It only acts as a hub, with one
    port being wireless.
  11. Joerg

    Joerg Guest

    However, that won't fix this problem. Strong signals don't mean much in
    multipath. Same with the TV where often an analog channel comes through
    strong and clear but their ATSC says "no signal".

    It always connects alright and the signal is strong but then randomly
    cuts out anyhow, for about 30-60secs at a time. Very annoying. I tried
    to place the AP in different rooms but since they are all heavily
    insulated the problem is more or less always there. RF bouncing back and
    forth I guess. An AP smack dab in the living room would not likely pass
    the inhouse permit process, SWMBO would loudly object ;-)

    I wish they'd look for data integrity instead. In multipath you can have
    a strong signal with lousy data integrity and a weak one that's
    excellent. For example, the local Ch29 digital almost has the field
    strength to light a CFL in the box but the picture falls apart all the
    time. A few Bay Area channels 100 miles away are weak but work most of
    the time. Of course, TVs don't have any data integrity indicators either
    so it's a wild guess whether you can watch a movie to the end or not.
  12. Joerg

    Joerg Guest

    I've heard some stations do that (not so much in our area though) but
    that sets them up for a serious black eye. Viewers buy new converter
    box, most don't have analog pass-thru, they tune in ... nada ... whoops
    .... numbers go down ... ad revenue goes down ... pink slips. In the
    current economic condition that almost amounts to suicide from a
    business point of view.

    Ch29 digital is where Ch48 used to be. On the analyzer it almost pegs to
    overload. But signal strength can mean nothing in this area.

    But it's all of them :)

    Did that already. It just keeps its beacon going. Traffic slows to a
    crawl. Seems to be trying but can't get through.

    Ah, thanks! Time to open it up and hanging the scope onto the rail. It
    appears to have a buck switcher that takes a wide input range. Of
    course, if the cap before the buck can't hold its water then it's all hosed.

    Not in this neighborhood, it's rather rural. But if I can't fix this
    quickly I'll just buy another one and try that.

    I've also tried at night where all the lights were off at the neighbors.
    Unless one of the kids snuck out and reach into the freezer ...

    The only option would be outdoors here. Inside it's like a metal maze
    from an RF point of view.

    Yeah, it might be needed. But right now it has to wait. My wife just
    started ripping out the floor in the next office. Meaning a slight hint
    "Hey, get over here with them tools, will ya?" If I was a bachelor I'd
    have left the old flooring in there and not moved a thing. But ...
  13. Joerg

    Joerg Guest

    It surprises me that station owners haven't created a ruckus in the
    media about that. Especially since they _own_ a media outlet.

    Another thing they forgot to tell folks is that frequencies will change
    and that they must run the auto-search again once the switch cometh. I
    don't want to be manning the phones in that week.

    Well, we got here two DTVs and two converter boxes, brand new. They all
    pretty much keel over simultaneously. Typically when clouds roll in or
    Fedex lumbers into Mather Field.

    All of the PCs with wireless in there do the same.

    It is an absolute nightmare to open that Linksys. Plus I need to fix the
    dang printer now, has all the supply voltages (I think) but won't work.
  14. SoothSayer

    SoothSayer Guest

    Jump online and find and buy a pair of better antennas. Problem solved.

    You also may be able to download third party firmware for it that allows
    you to boost the power beyond the factory, consumer accessible setting
    Also make sure you are using a newer, more secure access methodology.
    The old simple password, open broadcast method is insecure. Limit
    wireless ports to the number you use. You can also turn it on and off via
    an operating PC or even via web access, depending on your router.
    Well... it isn't 'true diversity'. You can also buy a long coax that
    allows you to place an antenna away from the actual router.

    The best thing to do is buy on ebay, an already upgraded router that
    runs Linux and the WRT firmware upgrade that allows you professional
    router setting and power levels on your consumer level router.

    That router is: The world famous Linksys (Cisco owned) WRT54GS v3 for
    max internal memory and CPU speed capacity. Mine was about $79 IIRC,
    shipped. I upgraded the firmware on it as soon as I got it, so I know it
    has nothing on it tucked away somewhere in the settings (these sellers
    are legit).

    Anyway, you can boost the piss out of it, if the new antennas don't

  15. Those damned round threaded fuses! You try soaking them out, you try
    scrubbing them out... and still you get... ring around the collar!

  16. No. It's an intranet router, and the other is your Internet side
  17. Your router WLAN is a LOCAL radiation device. You are not bouncing
    anything off the nearby hills that is interfering with your WLAN usage.

  18. Some had to erect VERY expensive antennas.
  19. Guest

    Maybe tack against the wind and -reduce- the Tx signal strength?. I.e
    hamstring some of the strong contenders fighting to open the door.
  20. Joerg

    Joerg Guest

    I know. You had snipped Jan's remark that he doesn't believe in
    multipath which I was responding to. If he had lived in this neck of the
    woods he'd know different. ATSC in heavy multipath is the pits.
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