Army interferes with garage doors.

[Reed]

read here:

[Arfa Daily]

Front end swamping ?

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

Arfa

[PeterD]

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?

[clifto]

For the same reason that all garage doors don't open when you push the remote for one.

[tnom]

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.

[Kurt Ullman]

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.

[mm]

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 :-)

[Sjouke Burry]

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.

[EXT]

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.

[S. Barker]

sounds like some bs to me.

s

[aemeijers]

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 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...

[Arfa Daily]

Why ??

Arfa

[Dave Platt]

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 :-)

[Michael Kennedy]

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

Mike

[clifto]

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

[DerbyDad03]

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

You know what happens when one assumes...

[Michael Kennedy]

My thoughts exactly. ;) I could open my garage door from anywhere in the state.

[Dave Platt]

I can't help envisioning the situation. Driver presses the "open" button, the car's engine labors and stalls under the load of powering the amplifier, and the garage door snaps open so fast that it rams right through the back of the garage and skims out into the yard like a Frisbee (tm).

[Michael A. Terrell]

Have you ever looked at the circuitry in a garage door opener receiver? No pre-amp, not much more than a tuned circuit feeding the mixer. Some older units were TRF broadband, and used simple tone modulation.

[Michael Kennedy]

No, I've never taken one apaprt. I didn't realize that they were so simple, but then again I don't have a garage door opener, or a garage door for that matter.

Mike