"Garage door opener" remote

I believe that most commonly you will see them operating at, or around

433.920 MHz. This is one of the bands in which Part 15 operation is allowed.

The primary frequency-user here is military radar, and secondary is amateur radio. One occasionally sees stories about military radar operations disrupting peoples' garage door openers and car alarm/locking systems in some areas. The commonest problems seem to be "they don't work" (the strong radar signals saturate the receivers) but "undesired operation" occurs occasionally (garage doors opening "by themselves").

Disarming the anti-intruder mines and lasers? :-)

"Garage door opener", "car alarm key-fob", etc.

Your best bet is probably to open up either the transmitter or receiver and find the FCC Part 15 registration ID. You can look this up on an FCC web site and get at least some information about the frequency and modulation pattern.

Commonly, these days, each button push will transmit a "rolling code" packet... a header, a transmitter ID number, a sequence number of some sort, a button code, and (in good ones) a cryptographic authentication of some sort (cheaper ones omit this). The reciever is "trained" to accept a specific transmitter ID (or set of IDs).

The better ones have some sort of transmitter-specific secret (known to the receiver via the training/programming process) which creates a cryptographic "signature" in the packet that's difficult to spoof. The receiver validates this, and also looks at the sequence number to provide "anti-replay" protection, so somebody can't record one of your "open the garage door" transmissions and play it back later when you're away from home. For these, the training process requires giving the receiver both the transmitter ID and shared secret (and often the starting sequence number).

Cheaper/older ones lack this sort of strong signature authentication and anti-playback defense. There are plenty of stories about people using off-the-shelf receiver dongles (e.g. the RTL-SDR type) to receive transmissions, PCs to analyze them, and cheap transmitters to re-send them. Want to unlock your neighbor's car? Want to "fast forward" your neighbor's transmitter's sequence number a few thousand times, effectively locking your neighbor out of the car? Not hard to do, alas.

Hello, I find this VERY interesting. I won't go into the whole story since it is very long but I have a customer that has an alarm system that I installed. It has wireless sensors for doors and such. There has been a few times that the system does not receive signals from the transmitters for periods of time from 45 minutes to 2 days. During this time their garage door opener remote does not work unless you hold it in you hand reach up to within 18" of the opener antenna and then it will work.

During that time the problem or source can't be determined. In discussions with neighbors it has be determined that at least

4 others, next door and across the street have experienced the same with there openers.

Then it all stops and goes back to normal operation???

This happened about 2 years ago and then again about a month ago. That I know about that is.

Needless to say when it IS NOT happening it is absolutely impossible to find. When it IS happening it is absolutely impossible to find.

The openers have a red LED on the unit that is used for learning in a remote button. Normally it is off until it receives a signal from a remote to open. During these events the LED is solid red for the entire time frame. Then during the end of the event it starts to flicker and then off.

The security devices are on 319.5 Mhz and the door opener is on 318 Mhz.

Is there any thoughts here as to what other than Military Radar that could be causing this issue with such intensity in a small area??

There is a local airport with control tower about 2 miles away.

I say a small area (200' square box maybe??) but it could be effecting a larger area but I have no way to know or to find out without having a town meeting.

Any thoughts on the subject would be most helpful.

Thanks,

Les

Here's my two cents worth. My home town, Frederick, MD is host to Fort Detrick. Maybe 10 or 20 years ago they announced some change in their emissions (no details provided I believe) so that these garage opener type devices may malfunction. With a number of homes in close proximity of the base there were garage doors opening at will and remotes no longer functioning. I believe at that time there were many fixed code devices and few, if any rolling code devices. It's not clear to me if that makes a difference, but a rolling code may be more suseptable to jamming in that if enough triggers are received as valid I believe the rolling code can desync your remote requiring you to sync it up again.

If enough units use the same brand of receivers/remotes is it possible that frequent use causes rolling code collisions that desync remotes? I'm thinking the wrap around count is sufficiently large that this is a near impossibility.

Build or borrow a directional antenna for 318 MHZ, get a portable receiver that provides signal strength information, and go on a fox hunt.

Reminds me of when I found one day that my garage door opener would open, but not close the garage door. After waiting 5 minutes, it would then close it.

Turns out that replacing the incandescent bulb in the opener with a CFL bulb (yes that long ago) caused enough EMI to saturate the front end of the receiver and it would not longer work while the bulb was on.

I currently have LED bulbs in the other garage lighting and it works okay, but I guess the bulb physically in the unit, plus the probably crummy bulb design, was enough to kill the receiver temporarily.

So maybe there is an *unintentional* emitter somewhere that is causing the loss in sensitivity

Here in the US, amateur radio operators have privileges in the 222-225 MHz, and 420-450 MHz bands. Neither of those so close to 318/319 MHz that it should cause problems for well-engineered receivers... but security and door-opener receivers may not be terribly selective. Unless they have band-pass filters before their first RF stage, it's possible that a strong ham transmission from nearby might saturate the front end (which would make it far less sensitive to the signals it should be receiving). I'm not sure you'd see the "red light flashing" symptom in that case, but that depends on the circuitry in your receiver.

The 318-320 MHz range appears to have primary usage for fixed and mobile communication, and 326 upwards is an aeronautical navigation range. So, it's possible that airport operations are responsible.

Another possibility is leakage from a cable-TV system. Cable TV uses a very wide range of frequencies, putting stations on frequencies which have other over-the-air uses. If somebody's got a cable TV feed in their house which has been left "open", or (worse yet) connected in parallel to a TV antenna, they could be radiating a whole range of frequencies out into the neighborhood and causing interference.

You might want to consider investing a small amount of money in what's commonly referred to as an "RTL-SDR dongle" or "DVB stick". These are wide-range radio-frequency receivers with USB interfaces. There's plenty of open-source software which lets them be used as inexpensive spectrum analyzers/sniffers - either on a PC or on an Android tablet or phone. They're in the $20-$30 range, depending on quality and features.

With one of these dongles, a tablet/phone, and a simple two- or three-element handheld Yagi antenna cut for 318 MHz, you could go QRM-hunting. You could see a whole slice of the frequency spectrum (I think these dongles give you about 2 MHz at a time) and look for the origin of an interfering signal.

Some additional input. During the 2 day's of interference a couple of years ago I driving through the development and noticed a Cable Company truck sitting on a street a couple of blocks away. I stopped and talked to the tech and told him what was going on. I asked if there was any problems in the area. He said, no he was just do some basic service checks and that he had a device in his truck that can see if there were any issue as he drove around. I gave him my cell and asked him to drive past the address and if he saw anything odd to please call me. He never called be so I can only "assume" his equipment didn't see anything unusual for the parameters that would concern him. I would guess that the frequencies are outside what the equipment looks at.

Dave, I agree that the cost would be minimal to maybe get lucky and find the nasty RFI. Someone else suggested similar equipment/software. My problem is that I really don't know what to get other than your description. For me that is only a hint. What I would like would be to have the Mfg. Name and Model Number for the dongle and the name of the PC software that will bring up a screen with the "waterfall" screen as it was mentioned earlier by somebody.

Without that specific information I would be just guessing and more than likely get it wrong more than once. Now I understand the concern of promoting a product that might seem like a sales pitch but for the rookie I see too many mistakes that I could make.

So I respectfully request the following.

RTL-SDR Dongle Mfg. & Model#

Handheld Yagi antenna cut for 318 MHz Mfg. & Model#

Open-Source Software Name/version

I would be installing on my PC Laptop and using USB connection.

I am guessing something here will meet the requirements??

Thanks for any input.

Les

This is the only really reliable place to get a good quality product. There are many clones, most of which cut corners and have reduced performance. There are also other reputable brands that are not clones, but this is the original-and-best, by all accounts:

You might not need a Yagi - a dipole will probably suffice despite the bi-polar radiation pattern. And the dipole is telescopic so you can set it to the right length for the frequency you're looking at.

The software you need depends on what hardware you're going to use (Linux, Windoze, or Android phone are all acceptable answers).

CH

<snip>

And, for those who prefer to shop at ebay, here's RTL-SDR Blog's ebay store:

Danke,

The airport radion navigation is hardly the culprit: the 329.15 MHz to 335 MHz range is for instrument landing system glideslopes (ILS GS). The signals are directed to the approach sector and they are pretty low power (typically 2 t0 10 W).

This *looks* to be the item I bought as a "cheap admission price" to tinkering with SDR. It was relatively painless to get started and "write" my first receiver.

The dongle gets pretty warm, though. And, I'm not sure how much actual power it is drawing -- how well it would work in a "portable" application.

[I don't like the USB interface but this was a lot cheaper than some of the other radios I looked at -- with "better" interfaces]

If the effect is as localized as he suggests, I imagine he'll get "visible" results regardless of the antenna used; "Can you hear me now?"

But, he'll need something with a graphic display (unless he wants to write some code)...

[There are some other, more tightly integrated SDRs with displays. But, at considerably more money!]

A bit over a watt. They do get warm. A phone's battery will still run one for long enough for useful DF though.

There is software that displays a waterfall for all three operating systems I listed.

CH

As others have suggested, the RTL-SDR.com R820T2 RTL2832U dongle is a solid performer. Their $40 bundle (including several antennas) is a good all-in-one solution to get you started.

Nooelec makes a similar medal-case premium dongle that's also got a good reputation...

and they also offer bundles with antennas. Their prices are a hair higher than RTL-SDR.com, though.

I don't know of an inexpensive commercial one which is cut for this frequency band. If it were me, I'd make one myself out of scrap wood and copper wire :-)

Some years ago I made an antenna along the following lines, for use in the 2-meter band (144-148 MHz):

A similar design would work for 318 MHz. If you just cut all of the dimensions in half (elements half as long, and separated by half as much distance) it'd probably work.

As others have suggested, you may not need one. It's possible to do direction-finding pretty well on these frequencies using a technique called "body fade". You would:

(1) Connect the dongle to a simple antenna - the little magnetic-mount wire-whip antenna sold in the RTL-SDR and Nooelec bundles should work.

(2) Stick the mag-mount on a steel pie pan or something like that, to provide a ground plane and give you something to hold it by.

(3) Stand in a clear area, so you aren't close to building walls or trees.

(4) Hold the antenna a foot or so directly in front of your body, and observe the interference signal on you PC/phone/tablet screen.

(5) Slowly turn around in a complete circle, looking at the screen to figure out the direction in which the signal is _weakest_.

(6) When you are facing in that direction, the source of the signal is (approximately) directly behind you.

Take bearings like this from multiple locations, draw the resulting vectors on a map, and where the lines cross is probably near the source of the interference.

SDR# is the commonest one for Windows use.

On Android, I use an app called "RF Analyzer", which requires a second app called "Rtl-sdr driver". Both are available from the Play Store.

On a Linux PC I usually use gqrx.

He may find some success just repurposing one of his "modules" for its antenna; if THEY are "seeing" the signal, then the sniffer should similarly see it with the same sort of antenna (admittedly at a different signal strength)

I.e., one alternative way of doing this work is to just take an instance of the victim hardware around the neighborhood and watch to see where it misbehaves/behaves. This also gives you data on areas that may not have "subscribers".

Dave, This is VERY helpful. Thanks!!

Please understand my position on the current situation.

#1 - Presently there does not seem to be any issues with any bad RFI in the area.

#2 - My concern is much more with the Security System being compromised NOT the garage door openers.

#3 - The fact the Garage Door Open's are effected is what told me there was a bad RFI of some kind in the first place.

#4 - Yes, I believe that the bad RFI is being caused by someone with something in the local area. Not caused by aliens, military radar, TV tower, radio tower, Cable TV, etc. I could be proved wrong!!!

#5 - It would be nice to have something in hand that could possibly track or trace the bad RFI when it happens. The keyword is "when". It may never happen again in my life time. I am 74 years old.

#6 - Do I want to strain my brain (74 year old brain) to learn all the cool stuff that all the Ham Radio Electronic Geeks already know or want to know about the RTL-SDR equipment/antenna/software?? Not really!!

#7 - If all I had to do was to order it, get it out of the box, plug it in and it starts working and giving me some baseline data now, that IF and WHEN the person (in #4 above) plugged in his/her toy I might get there in time before he/she turns it off and actually zero in on a direction or maybe a house would be great!!

#8 - Based upon the information you and others have provided I will touch base with an old friend that has some Ham Radio experience and get his input and see if he wants to get involved.

Again, THANK YOU for the extra details and input. Very helpful for me and maybe for others that are reading this thread.

Have a good upcoming weekend!!

Les

And that's an example of an idea I should have suggested: get in touch with your local hams and see if any of them are interested in helping out with a hunt.

There's a whole special-interest-group subset of hams who are heavily into "foxhunting" - searching for weak signal sources by one means or another. Most foxhunts involve searching for low-power transmitters, cleverly (often evilly) placed by hams organizing the foxhunt. The same set of technology and skills makes foxhunters very good at locating sources of interference.

So, call up a local ham club or two, and ask if any of their foxhunters would be willing to give you a hand.

A decade or so ago, we had a problem with some of the 2-meter repeater systems in my area. There was a "wandering" interference signal, drifting through the repeaters' input frequency ranges, causing a nasty "buzz" at the tail end of peoples' transmissions.

The first fox-hunt team found the general area (an apartment complex in San Jose), suspected that the problem might be a TV antenna amplifier, but weren't actually able to find the source.

The second team (of which I was a part) used a spectrum analyzer and a directional antenna. I was able to pinpoint the likely location (one specific ground-floor apartment). The owner was "in", he was quite helpful, and a quick check showed that the interference went away when one specific Ethernet hub was unplugged. It was apparently radiating a harmonic of its oscillator-crystal frequency, and "turning the building wiring into a gigantic TV antenna" as the old advertisement used to claim. The signal was strong enough to cause a problem miles away!

I offered to swap him an 8-port hub, for his defective 5-port hub. He agreed, we made the swap, and the problem went away forever.

You're quite welcome!

The local amateur radio club recently located a massive source of interference that blanketed all the amateur bands with S9 noise, from

3.5MHz up well past 400MHz, for a kilometre radius.

It was one of the large LED sign panels on the boundary of a local high school. It's not on all the time, but if you live nearby, good luck hearing anything else while it's on.

Clifford Heath

As a side note story. Many many............ many many years ago when I had my CB radio in my car there was a issue on channel 19 (maybe) that someone had their mic key locked on channel. A few of us in the area went out scouring around trying to pin-point the culprit. We got together about 10:30pm and finally about 1:00am narrowed it down to a specific house. We walked up to the door and rang the door bell a number of times and woke up the inhabitants. The guy came to the door and it took a bit for him to clear the fog out of his head and then went to his radio equipment and un-keyed his mic. He was apologetic and went back to bed. As did the rest of those that were on the hunt.

Yes, those are the things that happen that the rest of the planet never realize what was going on or even care.

Les

As long as you aren't trying to get much gain a simple loop of about the right size will be good enough for a signal strong enough for jamming.