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!!

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.

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

Unfortunately, the US military uses it's equipment in other places, it seems, without bothering about homologations.

The FCC is, after all, only a USian agency.

RL

This story is from Denver, Colorado but is applicable to Alaska since we have so many military installations, the new missile defense project

at Ft. Greely not being the least. The ionospheric heaters located near Glenn Allan and the BMEWS radar located at Clear both have caused massive radio frequency interferences in the past. Just ask any pilot that has flown into the radar signal or long time residents of Glenn Allan. I live between Ft. Wainwright and Eielson AFB and often experience strange signals on my cell phone and through my upstairs TV.

During my time in the US Army I worked at a frequency monitoring station at Ft. Huachuca, Arizona where we attempted to find interference among the many military signals that operated during war time exercises. It was a futile attempt to say the least. Radio signal interference from the military's many transmissions can come from harmonic signals generated by two or more signals. These harmonic

signals are difficult to detect and correct.

What is not known is the long term health risks associated with the barrage of radio frequency signals that penetrate our body every day. Millions of these transmissions come from earth and satellite transmitters and grow in number. No one knows what the end result will

be.

I haven't seen Ft. Greely since I left the US Army in 1974. Are you working on the project, or just living near the old base?

Aren't those band segments reserved for military use worldwide by international agreement?

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 ;-)

...Jim Thompson

In alt.engineering.electrical Jim Thompson wrote: | On 3 Dec 2006 23:52:10 -0800, "zeez" wrote: | |>

|>Jim Thompson wrote: |>> 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. |>>

|> 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.

Garage-door openers are some of the worst RF gear around. Receiver selectivity and overload tolerance is crap. If they want to operate near military bands with garbage receivers, they shouldn't complain about being blanked.

John

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. 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)

from a former eccm tech...

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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.

| 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.

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.

When I was young, I hooked up a 5 wattt mobile CB directly to the antenna inputs of a portable B&W TV. Ended up frying the sucker (the TV, not the radio. :)

I wonder if they sell garage door openers and remotes that use challenge-response. It wouldn't be that expensivge to do.

I wonder if they sell garage door openers and remotes that use challenge-response. It wouldn't be that expensive to do.

I have problems with steel doors, and walls that use metal mesh for the stucco, so my range is crap.

I'v been considering some kind of IR replacement. Any available commercially?

...Jim Thompson

In alt.engineering.electrical zeez wrote: | | snipped-for-privacy@ipal.net wrote: |> In alt.engineering.electrical Jim Thompson wrote: |> | On 3 Dec 2006 23:52:10 -0800, "zeez" wrote: |> | |> |>

|> |>Jim Thompson wrote: |> |>> 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. |> |>>

|> |> 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.