Army interferes with garage doors.

Front end swamping ?

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

Arfa

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?

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

--
   If only there was a Republican running for President of the United States.

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

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.

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.

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 :-)

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.

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.

sounds like some bs to me.

s

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...

Why ??

Arfa

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 :-)

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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).

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...

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

Mike

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

--
   If only there was a Republican running for President of the United States.

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).

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

You know what happens when one assumes...