Military radio signal jams garage doors

OK...here is an example of what NOT to do when testing RF equipment. So if you were one of the unfortunate souls that had to open your
garage door manually, be happy it wasn't in the middle of a hail storm!!
Military radio signal jams garage doors By ROBERT WELLER, Associated Press Writer Sat Dec 2, 5:03 PM ET
DENVER - What do remote-control garage door openers have to do with national security? A secretive Air Force facility in Colorado Springs tested a radio frequency this past week that it would use to communicate with first responders in the event of a homeland security threat. But the frequency also controls an estimated 50 million garage door openers, and hundreds of residents in the area found that theirs had suddenly stopped working.
"It would have been nice not to have to get out of the car and open the door manually," said Dewey Rinehard, pointing out that the outage happened during the first cold snap of the year, with lows in the teens.
Capt. Tracy Giles of the 21st Space Wing said Air Force officials were trying to figure out how to resolve the problem of their signal overpowering garage door remotes.
"They have turned it off to be good neighbors," he said.
The signals were coming from Cheyenne Mountain Air Station, home to the North American Aerospace Defense Command, a joint U.S. and Canadian operation set up during the Cold War to monitor Soviet missile and bomber threats.
Technically, the Air Force has the right to the frequency, which it began using nearly three years ago at some bases. Signals have previously interfered with garage doors near bases in Florida, Maryland and Pennsylvania.
In general, effects from the transmissions would be felt only within 10 miles, but the Colorado Springs signal is beamed from atop 6,184-foot Cheyenne Mountain, which likely extends the range.
Holly Strack, who lives near the entrance to the facility, said friends in the neighborhood all had the same problem.
"I never thought my garage door was a threat to national security," she said.
David McGuire, whose Overhead Door Co. received more than 400 calls for help, said the Air Force may be able to slightly adjust the transmission frequency to solve the problem. If not, it will cost homeowners about $250 to have new units installed.
"The military has the right to use that frequency. It is a sign of the times," he said.
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In alt.engineering.electrical Igor The Terrible
| OK...here is an example of what NOT to do when testing RF equipment. | So if you were one of the unfortunate souls that had to open your | garage door manually, be happy it wasn't in the middle of a hail | storm!!
Why not?
I presume this is all operating as a secondary unlicensed spectrum user. The garage door company perhaps should have used some other frequency in the first place.
But I also worry about the fact that this was a small area. While it may well jam the door radios nearby, would this signal make it to the intended first responders all over the country?
I'm curious about the frequencies involved. Possibly it's not dead on the same one, maybe off by 1/2 MHz, and just overloading receivers as opposed to blocking the signal of the tiny transmitters. Adjusting the frequency a little wouldn't do any good.
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On 3 Dec 2006 16:07:56 GMT, snipped-for-privacy@ipal.net wrote:

Clear back in 1950, 390MHz was assigned to the military. But _some_ garage-door-opener companies have continued to use that frequency based on the FCC "low-power-non-interference" rule.
In COS the openers were simply over-powered by a high power military antenna located on Cheyenne Mountain.
BTW, Cheyenne Mountain Resort Hotel is a great place to stay while consulting in COS ;-)
...Jim Thompson
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On Sun, 03 Dec 2006 09:41:36 -0700, Jim Thompson

Unfortunately, the US military uses it's equipment in other places, it seems, without bothering about homologations.
http://www.cbc.ca/canada/story/2005/11/04/ottawa-signals051104.html
The FCC is, after all, only a USian agency.
RL
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legg wrote:

Aren't those band segments reserved for military use worldwide by international agreement?
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On Mon, 04 Dec 2006 07:22:24 GMT, "Michael A. Terrell"

For 'world-wide' arrangements, I think you'd have to consult the ITU. http://www.itu.int/home/index.html
For other US-Canada, US-Mexico and others: http://www.fcc.gov/ib/files/11_27_01/annual_rpt2001.pdf
Please do.
RL
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legg wrote:

ITU has only allocated subauthority, it is WARC that makes the big decisions.
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Jim Thompson wrote:

Hmm, I remember hearing of an incident of Sputnik screwing with garage door openers back in the day. :)
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I was a Senior in High School when Sputnik went up. I don't think RF garage door openers existed back then ;-)
...Jim Thompson
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In alt.engineering.electrical Jim Thompson
| |> |>Jim Thompson wrote:
|> |>> Clear back in 1950, 390MHz was assigned to the military. But _some_ |>> garage-door-opener companies have continued to use that frequency |>> based on the FCC "low-power-non-interference" rule. |>> |>> In COS the openers were simply over-powered by a high power military |>> antenna located on Cheyenne Mountain. |>> |> Hmm, I remember hearing of an incident of Sputnik screwing with garage |>door openers back in the day. :) | | I was a Senior in High School when Sputnik went up. I don't think RF | garage door openers existed back then ;-)
If not then, soon after. My grandfather's brother had a remote garage door opener in 1961. I can't say whether it was optical or radio as I was a bit too young then to consider it important. But I sure thought it was great. It might have been rather expensive at the time.
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snipped-for-privacy@ipal.net wrote:

And probaly without the modern coding remotes have today. (remember, computer took up entire rooms at this time. :) I wonder if the first RF garage door openers listened for a specific audio tone broadcasted by the radio transmitter, or simply responded whenever an RF signal was detected on its frequency.
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| | snipped-for-privacy@ipal.net wrote: |> In alt.engineering.electrical Jim Thompson
|> | |> |> |> |>Jim Thompson wrote:
|> |> |> |>> Clear back in 1950, 390MHz was assigned to the military. But _some_ |> |>> garage-door-opener companies have continued to use that frequency |> |>> based on the FCC "low-power-non-interference" rule. |> |>> |> |>> In COS the openers were simply over-powered by a high power military |> |>> antenna located on Cheyenne Mountain. |> |>> |> |> Hmm, I remember hearing of an incident of Sputnik screwing with garage |> |>door openers back in the day. :) |> | |> | I was a Senior in High School when Sputnik went up. I don't think RF |> | garage door openers existed back then ;-) |> |> If not then, soon after. My grandfather's brother had a remote garage door |> opener in 1961. I can't say whether it was optical or radio as I was a bit |> too young then to consider it important. But I sure thought it was great. |> It might have been rather expensive at the time. | | | And probaly without the modern coding remotes have today. (remember, | computer took up | entire rooms at this time. :) I wonder if the first RF garage door | openers listened for a specific audio tone broadcasted by the radio | transmitter, or simply responded whenever | an RF signal was detected on its frequency.
My guess would be an audio tone. A more advanced design would compare to a 2nd audio tone such that the 1st must be stronger. They did have a means to reject neighbors. I remember my uncle mentioning his neighbor (in an area of expensive homes) also having one of these and they did not operate each other. Being RF frequency selective would be a bit hard to do for such cheap electronics. I have no idea if the audio would have been AM or FM modulated, but my guess would be AM. Still, it could easily be FM with the 2 tone test where one has to be much higher than the other to reject all the background hiss from FM demodulation.
These days, I'd want to make one with a challenge response security system built in so "the code" itself is never actually sent. For example, the remote makes a request to the base, the base generates a random number, encrypts it, sends one or the other to the remote, the remote does the same if sent the number or decrypts if sent the result, and sends back its result for confirmation and action. As long as it's very hard to derive the key from those two pieces of data, it should be reasonably secure.
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On 5 Dec 2006 16:00:17 GMT, snipped-for-privacy@ipal.net wrote:

I can remember units from about 15 years ago... they had dip switches with 7 (bit) selections to set a code.
...Jim Thompson
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snipped-for-privacy@My-Web-Site.com says...

I don't remember how many switches (IIRC 10) but before the "opener codes now in use, Sears used a trinary code.
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Contemporary openers use a "rolling code" where the transmitter sends out an changing number every time you press the button. Initially you press a "learn" button on the receiver which allows its to sync up with the transmitter. After that, the receiver will only accept codes that are within some small boundary of where in the sequence it thinks the transmitter *should* be (it needs some margin in case people accidentally press the button a little early, or if the kids play with it, or...).
This approach prevents capturing & re-transmitting the same signal to get into someone's garage. However, at least in theory if you knew the garage door opener brand you might know the algorithm and hence be able to predict what the next code in the sequence is and generate *that* if you're trying to, e.g., rob the house. Fancier openers then still have DIP switches that must match at the transmitter and the receiver that feed into how the next number in the sequence is created, which prevents that particular attack.
At that point, for the average garage a physical attack becomes much more viable than somehow trying to track multiple transmissions to ascertain the DIP switch settings and break in electronically. It also keeps the garage door opener cheap in that it doesn't have to receive -- still only transmit.
--

For the older non-rolling code transmitters (that just transmitted a specific
binary or trinary word each time), I've seen an awful low that were just still
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Joel Kolstad wrote:

Richard Fynman was a physicist on the Manhattan Project and had a known interest in safes. He was asked to see if he could open a safe - the person with the combination was not there that day. This may not have been the Manhattan Project, but IIRC the safe was to protect classified information. He tried the default combination those safes were shipped with and it worked.
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Bud-- wrote:

When I was in the Army, years ago in North Africa, I once had to open a safe used for crypto equipment, after the owner had been transferred. The first thing I tried was his birthdate. It worked!
Many hackers get computer access by using "password" as the password.
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Garage door opener remotes don't have a lot of power. It won't take THAT strong of a signal to swamp it out and overload the receiver. It's a S/N issue.
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| I am curious as to if/how they are jamming those encoded "digital" signals | that garage door openers have used for the past 15 years. | | 1) If the military signals are interfering with those digital commands, then | the signal must be overwhelming the receivers - they surely are not sending | simultaneous multiple sets of "trains" of pulses that fool all those | receivers' security, weak as it is.
I'd guess it most likely is an overload of cheap receivers.
| 2) If they are overwhelming the digital receivers instead of "stealing the | codes" so as to make them not work, they must be pumping out one hell of a | lot of power, relatively speaking - and that means the residents are being | subjected to the same steady barrage of RF. | And from days past, memory had the 390M range as not being particularly | friendly to humans (you don't feel anything until after any damage is done) | | 3) And curiously - if it jams the local garage door openers so well, why | isn't the miltiary using them in Iraq to jam the IED | detonators? -(apparently GDO remotes are the new favorite detonator of the | anti-US forces in Iraq)
Good question. It might need to be on a very close frequency for the overload to be effective by getting through the first stage filter. Maybe the IEDs get set up with a variety of unanticipated frequencies. It might be needed to be within less than 1% of frequency to be able to do an effective overload.
A base station probably could not do this overload for other than its immediate area. That would mean putting the transmitters on the field vehicles. But as soon as they do that, expect some RDF missles to start showing up in the hands of insurgents, if they figure it out.
BTW, I've actually overloaded a couple GFCI receptacles with my 2 meter hand held ham radio transmitter running at 5 watts to a rubber duck antenna at a distance of 10 feet. Those things really freak out when that happens. It could have been a resonance in the wiring.
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