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Army interferes with garage doors.

Discussion in 'Electronic Repair' started by Reed, Mar 8, 2008.

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  1. Reed

    Reed Guest


    read here:
    http://www.ddc.dla.mil/news/2005_02_15_FCC_Garage_Door.pdf
     
  2. Arfa Daily

    Arfa Daily Guest

    Front end swamping ?

    Garage door openers are coded so that your remote doesn't open every door in
    the street ??

    Arfa
     
  3. PeterD

    PeterD Guest


    No, they don't. Shared and the primary user (military) has priority,
    all non-primary users much accept any interference generated by the
    primary user.
    Well, if two signals could occupy the same frequency, we'd only need
    televisions with one channel, right?

    OK, so your car's FM radio picks up a given station. It picks up the
    strongest station, in fact if that strongest station were to suddnly
    stop transmitting (say a power or equipment failure) you'd then
    probably pick up the next strongest station on the same frequency...
    Strongest wins, in this and in fighting.
    Huh? So the military signal overpowers the remote... How's it going to
    work?
     
  4. clifto

    clifto Guest

    For the same reason that all garage doors don't open when you push the
    remote for one.
     
  5. Garage door openers (and a bunch of other household electronic devices
    (e.g., cordless phones, computers, wireless networking systems, wireless
    remote temperature/humidity sensors) are unlicensed devices governed by
    Part 15 of the FCC regs. They must not interfere with licensed services
    but must put up with any interference from licensed services. So if your
    garage door opener interferes with your ham-radio neighbor's
    communications, it's your responsibility to fix the problem (e.g., by
    replacing or refraining from using the offending device). Similarly, as
    long as your ham-radio neighbor is operating within the terms of his/her
    license and you keep hearing him/her in your cordless phone, that again
    is your problem -- although he/she ought to be willing to assist you in
    finding a solution to the problem (but is under no obligation to
    actually fix the problem or pay for somebody else to fix the problem).

    Perce
     
  6. Guest

    As someone else stated the front end of the garage door openers
    receiver is being swamped by a strong signal. This signal need not
    be the same frequency. It only has to be very strong and dilute the
    remote so that it can not be picked up.
     
  7. Kurt Ullman

    Kurt Ullman Guest

    Sorta like what happens when you are trying to use FM channels to
    listen in your car to the portable iPod or satellite radio. You get a
    strong station even a couple of channels over and you have to retune,
    often to the other end of the spectrum.
     
  8. mm

    mm Guest

    Today on the news I heard that a big bunch of electronic garage door
    openers weren't working in Churchville Maryland because the govt. at
    the Aberdeen Proving Grounds was doing something with a satellite or
    something. Tomorrow their going to do the same thing around Aberdeen.

    People are paying techs to change the freqs, but some may have paid
    for other repairs by mistake, one would assume.

    Someone in charge admits he didn't get the word out well enough.

    1) Don't they assign frequency ranges to things so that this sort of
    thing doesn't happen?

    2) How could the use of a frequency mess up the garage door openers?
    Even if the govt. signal was stronger, why wouldn't the opener still
    work? If the govt. signal was picked up by the opener, how come the
    doors didn't open or shut. (Apparently they didn't since they would
    surely have mentioned that.)


    If you are inclined to email me
    for some reason, remove NOPSAM :)
     
  9. Sjouke Burry

    Sjouke Burry Guest

    I have used these openers for datatransmission, and the type I used
    had 8 tri_state codeswitches.
    If the code does not fit, nothing happens, when some outside transmitter
    intervenes.
    The codestring contained about 42 bytes in total, and it is difficult to
    trigger that with some random signal.
    In case of interference, you just have to get closer to your receiver,
    for it to work.
     
  10. EXT

    EXT Guest

    This is the same sort of problem that some Chrysler cars had in the 90s. If
    you drove by a powerful radar installation, and the beam hit your car, it
    would stall due to interference with the electronic ignition/computer
    components in the car. The car manufacturer had to come up with a
    modification to harden the engine's controls to the radar signal.
     
  11. S. Barker

    S. Barker Guest

    sounds like some bs to me.

    s
     
  12. aemeijers

    aemeijers Guest

    Must be a slow news day in Maryland- this has been going on for years,
    at multiple bases, and even at some civil airports. Like others in the
    thread have said, homeowners are legally SOL- low-power non-licensed
    consumer devices are not protected. Megawatts versus milliwatts, the
    big-ass transmitter will simply overpower the tiny one. Sometimes
    repositioning or changing the length of the antenna pickup wire attached
    to the opener can help. Sound like the local garage door companies have
    their shears out.

    Did the article say if the base was working with the locals, to maybe
    fine-tune reality a tad, and move their transmitter to a freq that would
    cause less problems, or reorient the transmitting antenna? They aren't
    obligated to, but base commanders <hate> having the locals all pissy
    with them. They have done that at some bases, to include providing the
    local media with how-to guides about moving the antenna wire in the
    garage and such.

    aem sends...
     
  13. Arfa Daily

    Arfa Daily Guest

    Why ??

    Arfa
     
  14. Dave Platt

    Dave Platt Guest

    Not really. The garage door openers are "Part 15" devices - they
    don't have a reserved frequency allocation. Instead, they (and other
    low-power devices) are allowed to use a wide range of frequencies that
    are primarily allocated for other radio services.
    A lot of unlicensed (Part 15) devices such as garage door openers and
    car-alarm keyfobs use frequencies around 433.920 MHz.

    The primary usage allocation for this frequency band is government
    echolocation (radar). Ham radio operators have a secondary allocation
    (i.e. they can use it as long as they don't interfere with government
    radar). Unlicensed users are tertiary, and have *no* legal protection
    against interference from licensed, or other unlicensed users.

    The transmitters for these Part 15 devices use very low power, by
    design and law. The receivers for them are, well, let's say
    "inexpensively made" - they tend to be reasonably sensitive (so that they
    can pick up the weak signals from the transmitters) but are not at all
    selective.

    Strong signals from other transmitters, on the same or nearby
    frequency bands, can overload (saturate) the RF front end circuitry in
    these receivers - a phenomenon known as desensitization or "desense".
    When this happens, a strong transmission can completely block the
    weaker one, even if the actual frequencies of the two transmissions
    don't overlap at all. It's sort of like trying to hear a low-pitched
    voice speaking quietly in the next room, when somebody is blasting
    your eardrums with a piccolo :)
     
  15. noespaem

    noespaem Guest


    the base is under no obligation to do anything. some base commanders
    have chosen to create more trouble for themselves by attempting to
    accomodate the "locals". they then discover the cost associated with
    any "mitigation" strategy to be cost prohibitive.

    there is no one single "transmitter". there are several - these are
    Motorola digital APCO P25 trunking systems. a "control channel" is
    continously transmitting 24/7. the other transmitters will key up
    to carry voice traffic as needed (as assigned by the central controller,
    the "brains" of the system).

    it is NOT a simple process to modify the frequency bandplan due to
    the domino effect on the rest of the system. trunking central controllers
    would need to be reprogrammed, databases changed, subscribers (ie. the
    hundreds of portable walkie talkies and mobiles in the field) would need
    to be bought in and reprogrammed, and RF transmit combiners would need
    to be retuned. These are NOT simple tasks !

    "reorienting" an antenna is not going to work either. the coverage
    on these systems is OMNI directional (ie. we strive to provide a perfect
    circle, if possible). the typical goal is >95% coverage for a portable.
    in practice, we can usually achieve numbers greater than that.

    now, if a spineless base commander wants to pay the several hundred
    thousand dollars to do a new engineering study and then the actual
    man hours involved in implementing a frequency change (that they are
    under ZERO obligation to do), then i'm sure the vendor (Motorola) would
    be more than happy to accomodate them - just show them the money !

    however, it's unlikely any new frequency within the assigned govt.
    spectrum will solve the problem. you're always going to have some
    part 15 device affected.

    the answer is better engineering on the consumer side (ie. move the
    devices to another frequency band, and tighten up the front end
    selectivity on the receiver).
     
  16. aemeijers

    aemeijers Guest

    Don't know about the current case, but the ones previously written up
    were NOT LMR systems, trunked APCO p25 or otherwise- they were radar r&d
    sites. One of my duties at work is buying LMR systems, so I do
    understand how those work. (or in the case of the local public safety
    LMR, NOT work.) I've never heard of a trunking control channel causing
    problems for garage door openers- the repeaters just aren't that
    powerful. I suppose it is possible, but reorienting the antenna for the
    part 15 device usually would fix that.

    No, a base commander is not gonna break his budget or compromise mission
    capability to keep the locals happy. But since 'having a good working
    relationship with local civil authorities' is one of the things he gets
    rated on, he isn't gonna tell them to eff off, either. Having a senior
    tech and a PR flack give a few tours, and provide info to local media,
    can go a long way.

    aem sends...
     
  17. Or get a signal amplifier, although I'm sure that is not legal.

    Mike
     
  18. clifto

    clifto Guest

    That's it, a garage door opener transmitter with a 500-watt linear amplifier.
     
  19. noespaem

    noespaem Guest


    the new system at Eglin AFB ran afoul of some locals in the
    developments nearby (who discovered their garage door openers
    were being hit with the equivalent of a jammer - the emitter
    being the control channel of the new trunking system).

    there have been other reports of similar spectrum issues at
    other installations.

    now in a different reverse case, the military is claiming
    amateur radio repeaters are interfering with some PAVE PAWS
    radar sites. which the ARRL is cooperating with them to
    address the issues.


    is "MA/COM" in that scenario ?

    typical output on a licensed transmitter is approximately 55 watts
    out of the transmit combiner to, say a 100' high, 7 db gain antenna. so
    anyone can do the math here. a nominal receiver sensitivity number
    for receiver 5% BER (on the subscriber side) is probably about -120 dbm
    of signal.

    the "average" part 15 consumer device is hard of hearing to begin
    with (compared to a $4000 high end Motorola unit). so it has some
    attenuation hearing it's intended signal (the remote) to begin
    with. flooding the area with the control channel signal only adds
    to the noise mask the garage door receiver would need to struggle
    against.

    also keep in mind, these systems operate in the spectrum slots
    assigned to US federal govt users. so, it's not going to be the
    800 mhz, or 450-512 band slices.

    the remote manufacturers rolled the dice (on operating on frequencies
    that could be reclaimed by the govt at anytime), and they lost.
    unfortunately the consumer is caught in the middle. of course,
    the manufacturers specifically have wording in their manuals that
    address the possibility of interference and disclaim all liability
    for same.


    see above, maybe, maybe not - probably not.


    agreed, most CO's are politically savvy (unfortunately so in some cases,
    but we won't go there).
     
  20. DerbyDad03

    DerbyDad03 Guest

    re: some may have paid for other repairs by mistake, one would
    assume.

    You know what happens when one assumes...
     
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