Mystery Frequency Disrupted Car Fobs in an Ohio City, and Now Residents Know Why(nytimes.com)
nytimes.com
Mystery Frequency Disrupted Car Fobs in an Ohio City, and Now Residents Know Why
https://www.nytimes.com/2019/05/04/us/key-fobs-north-olmsted-ohio.html
126 comments
The answer (excerpted from the linked article):
Without verbatim:
The source of the problem was a homemade battery-operated device designed by a local resident to alert him if someone was upstairs when he was working in his basement. It did so by turning off a light.
“He has a fascination with electronics,” Mr. Glassburn said, adding that the resident has special needs and would not be identified to protect his privacy.
The inventor and other residents of his home had no idea that the device was wreaking havoc on the neighborhood, he said, until Mr. Glassburn and a volunteer with expertise in radio frequencies knocked on the door.
“The way he designed it, it was persistently putting out a 315 megahertz signal,” Mr. Glassburn said. That is the frequency many car fobs and garage door openers rely on.
“There was no malicious intent of the device,” he said in a statement.
The battery on the device was removed and the signal stopped. “It was a relief,” Mr. Glassburn said.
The source of the problem was a homemade battery-operated device designed by a local resident to alert him if someone was upstairs when he was working in his basement. It did so by turning off a light.
“He has a fascination with electronics,” Mr. Glassburn said, adding that the resident has special needs and would not be identified to protect his privacy.
The inventor and other residents of his home had no idea that the device was wreaking havoc on the neighborhood, he said, until Mr. Glassburn and a volunteer with expertise in radio frequencies knocked on the door.
“The way he designed it, it was persistently putting out a 315 megahertz signal,” Mr. Glassburn said. That is the frequency many car fobs and garage door openers rely on.
“There was no malicious intent of the device,” he said in a statement.
The battery on the device was removed and the signal stopped. “It was a relief,” Mr. Glassburn said.
We're getting to the point where simple devices without the full range of security capabilities just aren't tenable anymore. Wireless devices should be securely keyed. The protocols cannot expose the key. They should be immune to replay attacks and eavesdropping. They should also be immune to simple jamming.
It's like how people in the country in most cases can have a wood fire, and it's no problem. Get to the population density of the city, and backyard wood fires become the major source of particulate air pollution. It's like how in the early days of electricity, there were to GFCI safety devices and everything was just bare conductors on ceramic insulators nailed into wood. We're not in those days anymore.
It's like how people in the country in most cases can have a wood fire, and it's no problem. Get to the population density of the city, and backyard wood fires become the major source of particulate air pollution. It's like how in the early days of electricity, there were to GFCI safety devices and everything was just bare conductors on ceramic insulators nailed into wood. We're not in those days anymore.
He's lucky a local ham investigated and not the FCC.
I think if it's a free frequency you can do whatever you want, no? I mean I use 433Mhz in my house to do some communications between devices and I think I don't need any authorization from someone.
Or is it the power that is limited? (Which makes a lot of sense)
Or is it the power that is limited? (Which makes a lot of sense)
Part 15 (unlicensed frequencies used for communication) still has rules. There is a hobby exemption for up to five devices--however, that is an exemption to the testing requirements, not the rules themselves--and you are still required to use "good engineering practice" like not designing it to have the transmitter run continuously. There are also pre-certified modules available for things like wifi, zigbee, xbee, etc.
There is almost always a power limit, and there are often spread spectrum, usage type, antenna directionality, and other requirements. Additionally, licensed users need For 433 MHz in the US, you have two allowed usage rules: 47 C.F.R. 15.240 [0] and 47 C.F.R. 15.231 [1]. The former is for transportation use only. The latter is what car remotes use, and your usage probably falls under that as well. Among other requirements, you can transmit for no more than 5 seconds--unless they are signalling an emergency alarm condition. If you don't follow either part there is a very minimal power output that is generally not useful for wireless data transmission.
[0] https://www.law.cornell.edu/cfr/text/47/15.240 [1] https://www.law.cornell.edu/cfr/text/47/15.231
There is almost always a power limit, and there are often spread spectrum, usage type, antenna directionality, and other requirements. Additionally, licensed users need For 433 MHz in the US, you have two allowed usage rules: 47 C.F.R. 15.240 [0] and 47 C.F.R. 15.231 [1]. The former is for transportation use only. The latter is what car remotes use, and your usage probably falls under that as well. Among other requirements, you can transmit for no more than 5 seconds--unless they are signalling an emergency alarm condition. If you don't follow either part there is a very minimal power output that is generally not useful for wireless data transmission.
[0] https://www.law.cornell.edu/cfr/text/47/15.240 [1] https://www.law.cornell.edu/cfr/text/47/15.231
Even if part of the spectrum is unlicensed, you're still bound by power limits.
And lack of interference to other services
Nope.
If it's an FCC class B, YOU must accept interference from otherwise approved class B compliant devices. Class B is a very low threshold for that. Mostly it's power limits and not much else.
Key fobs, if you look at the fine print, are Class B.
There are also exemptions for certain experimental or lab devices though you can't break power limits with those as narrowly defined by regulation.
But if you happen to have your Class B device too close such a device, that's entirely your problem, the user of the Class B device.
This is a common issue with ham radio: they actually are allowed to interfere with Class B but it's a political decision that drives most of ham radio to "play nice". Legally they have seniority when it comes to interference and the law when it comes to Class B devices. Basically you are screwed with Class B in most cases with little legal recourse.
And Class B is such a low threshold that 99% of the time such interference is actually due to bad design or use of cheap components in the Class B device itself. In this case, the fobs. Same goes for TVs, broadcast radio receivers, etc.
No one has a right to zero interference from other RF sources for the most part! Mostly because it's physically impossible to assure or deliver! There's merely a regulatory threshold for the extremely bad and summarily interfering levels of RF power.
If it's an FCC class B, YOU must accept interference from otherwise approved class B compliant devices. Class B is a very low threshold for that. Mostly it's power limits and not much else.
Key fobs, if you look at the fine print, are Class B.
There are also exemptions for certain experimental or lab devices though you can't break power limits with those as narrowly defined by regulation.
But if you happen to have your Class B device too close such a device, that's entirely your problem, the user of the Class B device.
This is a common issue with ham radio: they actually are allowed to interfere with Class B but it's a political decision that drives most of ham radio to "play nice". Legally they have seniority when it comes to interference and the law when it comes to Class B devices. Basically you are screwed with Class B in most cases with little legal recourse.
And Class B is such a low threshold that 99% of the time such interference is actually due to bad design or use of cheap components in the Class B device itself. In this case, the fobs. Same goes for TVs, broadcast radio receivers, etc.
No one has a right to zero interference from other RF sources for the most part! Mostly because it's physically impossible to assure or deliver! There's merely a regulatory threshold for the extremely bad and summarily interfering levels of RF power.
Putting out a square-wave 315mhz signal can be very broad and hit other non-Class B devices.
Regardless of class, spurious emissions are not permitted.
Regardless of class, spurious emissions are not permitted.
And duty cycle limits.
There are several limitations for 433Mhz.
If i remember correctly the main two are: - Power limits - Transmission length per interval of time (I believe max 300ms in any 10s window)
If i remember correctly the main two are: - Power limits - Transmission length per interval of time (I believe max 300ms in any 10s window)
I think this land isn't owned so I can dump anything I want on it, right?
I really hope that someone who knows more about electronics could help the guy to get a better understanding of what he did wrong and how he could do it in a better way.
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Would be interesting to get a better understanding of how it worked. I’m assuming there was a motion sensor upstairs, though I don’t understand why it would send a constant signal.
There's a good chance the relevant code was running inside loop() in an Arduino sketch and "whohoo; it works!" represented the end of development on the project.
I'm assuming he also didn't account for harmonics. It'd be interesting to see how dirty his transmissions made the spectrum.
Given that he took out 315MHz in a pretty wide area, I'm wagering he was using a specific 315MHz module and was just transmitting a near-constant signal. (A duty cycle issue rather than a harmonics issue.)
Something like this: https://www.aliexpress.com/item/NEW315mhz-rf-Transmitter-and...
Something like this: https://www.aliexpress.com/item/NEW315mhz-rf-Transmitter-and...
Also don't rule out an incredibly poorly made 315Mhz transmitter. Chinese companies will see lots of bad reviews on their 315Mhz breakout board like, "Terrible product! Only works from within like 3 feet from the transmitter."
So management gets mad at the engineer (who likely has no formal training or knowledge of FCC regulations) and says, "fix it!"
"OK OK I'll just crank up the power!"
Version 1.1 of the board is released on AliExpress a week later ("New version of board. We fixed weak signal!").
End users start getting the new board and like magic they can pick up a signal from like a mile away!
So management gets mad at the engineer (who likely has no formal training or knowledge of FCC regulations) and says, "fix it!"
"OK OK I'll just crank up the power!"
Version 1.1 of the board is released on AliExpress a week later ("New version of board. We fixed weak signal!").
End users start getting the new board and like magic they can pick up a signal from like a mile away!
Then the FCC comes knocking?
FCC can’t really do anything about a Chinese person selling from China
They can if someone is importing it.
Most hobbyst (at least where I live) order directly from China on ebay or aliexpress. It's cheapest this way.
Customs services worldwide probably won't even come close to inspecting even 1% of that unending stream of tiny plastic envelopes containing some sort of electronics heading for thousands of local hobbyists. It's a logistical impossibility.
They could blacklist everything and only pass-through stuff sent by trusted exporters I guess. Check 1% of the packages, if some exporter lied revoke his trusted status.
But I highly doubt they will do it :)
But I highly doubt they will do it :)
That's what I do it almost all my equipment (not US, though)
They can send a BOLO to CBP and have the devices seized on import.
Why do you assume there was a microprocessor involved at all? Most PIR sensors come as modules that operate either with a normally open or normally closed trigger pin and a couple of pots for adjusting sensitivity and trigger duration.
It would be easy to build a transmitter to blast out a constant high pulse and then just cut it off using a transistor or mosfet hooked up to the trigger on the PIR.
Simple circuit with no microprocessor or coding required.
It would be easy to build a transmitter to blast out a constant high pulse and then just cut it off using a transistor or mosfet hooked up to the trigger on the PIR.
Simple circuit with no microprocessor or coding required.
Like all the best projects.
This is probably how it worked: https://www.rtl-sdr.com/transmitting-fm-am-ssb-sstv-and-fsq-....
and how it also had unintended consequences. Note how many comments there are from people who don't seem to have understood the disclaimer. I'd bet our rogue dongle-jammer was in much the same boat :)
and how it also had unintended consequences. Note how many comments there are from people who don't seem to have understood the disclaimer. I'd bet our rogue dongle-jammer was in much the same boat :)
I see, so it was constantly broadcasting and then he’d encode some message in the signal to indicate if someone was up stairs, instead of only broadcasting when there was a message to send. That certainly would explain it.
That certainly exacerbated it, but arguably it's not even the worst RF sin being committed here. The other is spurious emissions. Toggling a GPIO at frequency f doesn't just result in frequency f, it also results in 3f, 5f, 7f, and so on because the GPIO is outputting a square wave not a sine wave. That's the best case. Unreliable timing could turn that from a frequency "comb" into a forest of spurs across the RF spectrum, and whichever spurs make it out of an antenna are going to break the law (best case) or interfere with important RF devices (worst case).
You're probably right that they used a guide like that. It seems irresponsible to publish that blog post. 99% of Pi tinkerers will read that disclaimer in the third paragraph and either not understand that life critical devices _do_ can be interfered with or think their use-case is special/low-powered and won't do any harm.
The irresponsible part is that he says you "must use a filter" if you attach an antenna but does not describe what that would entail. There's not even a link anywhere that would describe how to make a filter or even what he's talking about ("I have a filter... There's no bad power going into this thing!")
When you, "make something dangerous easy" you have a responsibility to be very specific in how to use your invention safely. Otherwise disaster seems inevitable.
When you, "make something dangerous easy" you have a responsibility to be very specific in how to use your invention safely. Otherwise disaster seems inevitable.
You can buy razor blades almost everywhere for like a dollar.
(Reviewing this comment later I see it can be read in sort of a nasty way; my meaning was that we don't really assign blame to providers of dangerous tools, the low price of razor blades reflects this)
(Reviewing this comment later I see it can be read in sort of a nasty way; my meaning was that we don't really assign blame to providers of dangerous tools, the low price of razor blades reflects this)
So they are generating a signal by toggling the IO pin on and off. Not only will there be a huge amount of harmonics, wouldn't processor interrupts wreak havoc on the output signal and cause even more interference?
Yes and no; if they're doing it right, they're using the DMA or PLL engine which runs independent of the main CPU/ALU. See https://github.com/F5OEO/PiFmRds "This version modulates the PLL instead of the clock divider for superior signal purity. The harmonics are unaffected, so the legal warning still applies."
Filtering this stuff isn't hard, but I'm realizing there aren't any good stone-simple tutorials for it. Might have to write one.
Filtering this stuff isn't hard, but I'm realizing there aren't any good stone-simple tutorials for it. Might have to write one.
I've done a hobby project where I'm using pure RPi GPIO to drive a servo motor with PWM, so processor interrupts would ruin my day. So I can tell you that the rate at which modern Linux interrupts a running application is massively overstated. If your system is configured right, that happens maybe two or three times a second at most.
If you're running on a dedicated core, as you should, 99% of the time your application just happily runs along.
If you're running on a dedicated core, as you should, 99% of the time your application just happily runs along.
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Can someone explain to me why generating a square wave creates lots of harmonics, as opposed to other kinds of waves?
The spectrum of a signal is its Fourier transform. Only sine and cosine signals have a "pure" signal with a single frequency. Anything else decomposes into a whole host of spectral contributions. Square waves are especially bad because they require contributions from infinitely many harmonics to produce the steep flanks. That is also why a clean square wave cannot exist: some kind of band limit is always present, resulting in ringing around the flanks.
See also Fourier Analysis on the Wikipedia article: https://en.m.wikipedia.org/wiki/Square_wave
See also Fourier Analysis on the Wikipedia article: https://en.m.wikipedia.org/wiki/Square_wave
Because you try to generate a square wave by adding toghether "round" waves (sinusoidal). In order to get into the "corners" you must add "round" waves with smaller and smaller diameters (period). Small periods means high frequencies. The more waves you add, the squarer the sum becomes.
A square wave IS the base frequency plus ALL[1] the odd harmonics (https://en.wikipedia.org/wiki/Square_wave#Fourier_analysis explains it better than I could).
[1]: Yes, so in reality you neither get an infinite set of harmonics, nor a perfect square wave.
[1]: Yes, so in reality you neither get an infinite set of harmonics, nor a perfect square wave.
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FYI: quoting material like that is impossible to read on mobile because it does not wrap. Please just use ">" as an quotation marker.
I'm aware, and consciously chose this because in this case I thought that preformatted was clearer. But perhaps I'm wrong. What percentage of people use mobile for HN? Is there a reasonable column width that works for 95% of them?
Edit: OK, I just looked at it on a phone. Yes, it looks bad, and that the lines would have to be about half the length to be readable. Too late to edit this one, but I'll try to switch to italics or '>' in the future for everything except for code samples.
Edit: OK, I just looked at it on a phone. Yes, it looks bad, and that the lines would have to be about half the length to be readable. Too late to edit this one, but I'll try to switch to italics or '>' in the future for everything except for code samples.
I get 26 characters portrait, 40 landscape.
I almost exclusively read HN on mobile, occasionally emailing things to myself to do on a desktop/laptop later.
I almost exclusively read HN on mobile, occasionally emailing things to myself to do on a desktop/laptop later.
On the other hand reader mode for FireFox temporarily fixes the bug.
I’d wager it’s a pretty high percentage. HN works great on mobile aside from this. There’s no reasonable column width, just use quotes for quotes.
Hard-wrapping to some column width only ever really works when you know the physical width of the screen/paper. Otherwise, dynamic soft wrapping.
I hate preformatted text in HN comments (and I never even read HN on mobile).
FYI: quoting material like that is impossible to read on mobile because it does not wrap. Please just use ">" as an quotation marker.
or wrap it in * to italicize
or wrap it in * to italicize
I kinda wish HN could fix that... We hear this all the time and yet its still broken. They add other things to HN but a subtle bug fix would be welcomed.
Not "impossible", you just have to scroll horizontally (I read it on my mobile device).
It's possible to read on mobile. It may not wrap but you can scroll it horizontally (Chrome on Android)
If you have ever wondered why they tell you to turn off electronic devices during take off and landing, here it is.
Wireless activation for this is overkill, you could build this with some romex, a PIR sensor, a relay, a single-pole switch, and a light fixture for around $50, $75 if you don't have a fish stick to fish the romex through the walls.
Or I could hook the same sensor and relay up to a pair of $5 transceivers.
Avoiding going into the wall isn't overkill, especially if it's cheaper and faster.
Avoiding going into the wall isn't overkill, especially if it's cheaper and faster.
Cutting thru the clickbait:
Someone built a homemade light control system that operated at 315Mhz, and caused interference with many other devices.
I hate clickbait but that doesn't mean any article needs to be reduced to fit in a headline so no one has to read it in order to qualify as non-clickbait.
the headline omits basic critical information that could easily be included in the headline. They could have just as easily written it "Source of Mystery frequency disrupting car fobs in an Ohio city was homemade electronics project".
The title is 100% clickbait. I refuse to read content with clickbait titles so thank you OP for the summary.
I wouldn't entirely call it clickbait. The article does a nice job showing how difficult these problems can be track down and the consequences of a seemingly harmless action.
The article implies that it was hard to identify the source:
"Garage door repair people, local ham radio enthusiasts and other volunteer investigators descended on the neighborhood with various meters. Everyone agreed that something powerful was interfering with the radio frequency that many fobs rely on, but no one could identify the source."
But it doesn't really explain why it was hard. I would have expected that the ham radio folk would have quickly been able to pinpoint a steady source with no problems. Later in the article, it seems to imply that this was indeed the case:
"Dan Dalessandro, a television repairman, was one of several ham radio aficionados who went to investigate. At first, he said, all he picked up were “little blips” on a signal detector, but on one block — and at one house in particular — the signal was extraordinarily powerful."
This makes me doubt the accuracy of the article. Was it difficult to find the exact source, or not? Is there some reason that getting directionality on a constant 315 MHz signal is harder than one would think?
"Garage door repair people, local ham radio enthusiasts and other volunteer investigators descended on the neighborhood with various meters. Everyone agreed that something powerful was interfering with the radio frequency that many fobs rely on, but no one could identify the source."
But it doesn't really explain why it was hard. I would have expected that the ham radio folk would have quickly been able to pinpoint a steady source with no problems. Later in the article, it seems to imply that this was indeed the case:
"Dan Dalessandro, a television repairman, was one of several ham radio aficionados who went to investigate. At first, he said, all he picked up were “little blips” on a signal detector, but on one block — and at one house in particular — the signal was extraordinarily powerful."
This makes me doubt the accuracy of the article. Was it difficult to find the exact source, or not? Is there some reason that getting directionality on a constant 315 MHz signal is harder than one would think?
I could probably find such a transmission using my personal equipment in a relatively short amount of time. That’s all well and good, but you’re a city council person and a constituent complains. Then another, and another. Call up mikestew and his crack team of Rogue Transmission Finders? No, you went to business school, you haven’t the first clue how this shit works. I mean on the level of “it uses radio waves? Is it like WiFi on my computer?” cluelessness. Garage door people, though a good first guess and good folk who know how to fix that giant spring without getting killed, are not RF engineers. AT&T? phhhhttt, what, they’re sending their crack RF engineer into the field to diagnose a frequency that is not in their allotted bands? And everyone’s cell phone still works, so take a guess at what defined “best effort”.
So my guess is the vast majority of the time was spent tracking down someone with equipment and the knowledge to use it. Or probably more accurately, just finding the person who even knows who to ask in the first place.
So my guess is the vast majority of the time was spent tracking down someone with equipment and the knowledge to use it. Or probably more accurately, just finding the person who even knows who to ask in the first place.
Frankly I'm surprised he didn't get in touch with the car manufacturers. I mean, that's the device that was having issues!
GM, Ford, Toyota, etc would have troubleshooting guides at the very least but I wouldn't be surprised if they were able to narrow it down pretty quickly with a simple phone call...
"Well the fobs work on the 315Mhz spectrum. So I'd start by looking for devices transmitting on that frequency."
If they did contact the car manufacturers and they didn't give him this basic advice then shame on them.
GM, Ford, Toyota, etc would have troubleshooting guides at the very least but I wouldn't be surprised if they were able to narrow it down pretty quickly with a simple phone call...
"Well the fobs work on the 315Mhz spectrum. So I'd start by looking for devices transmitting on that frequency."
If they did contact the car manufacturers and they didn't give him this basic advice then shame on them.
You have a very high opinion of car manufacturers.
To be blunt, once a car rolls off the dealer lot, they don’t care. If it’s so bad that experts are really required, you take the car to them, they run through checklists, done. I would bet good money that most garages don’t employ anyone who knows what a Mhz spectrum is, let alone what the fobs use.
To be blunt, once a car rolls off the dealer lot, they don’t care. If it’s so bad that experts are really required, you take the car to them, they run through checklists, done. I would bet good money that most garages don’t employ anyone who knows what a Mhz spectrum is, let alone what the fobs use.
Car manufacturers: Is it killing more than a 1000 people? Nah, we don't care.
I have a feeling it was weeks before someone with a clue stepped in, and then a matter of minutes.
315 MHz is a perfectly lovely frequency for direction-finding. Hams have "fox hunt" exercises around 440 MHz all the time, and 315 just means the optimal antennae are slightly larger, but still easily portable.
I've only participated in a few fox-hunts, but they're incredibly fun. Typically our "search area" is the bounds of a city, or a set of roads maybe 3-5 miles on a side, and our time frame is an hour. I have yet to see one where the fox isn't found within the hour, typically about half that, and in many cases the fox only transmits for 30 seconds every 5 minutes or something, just to make it harder.
315 MHz is a perfectly lovely frequency for direction-finding. Hams have "fox hunt" exercises around 440 MHz all the time, and 315 just means the optimal antennae are slightly larger, but still easily portable.
I've only participated in a few fox-hunts, but they're incredibly fun. Typically our "search area" is the bounds of a city, or a set of roads maybe 3-5 miles on a side, and our time frame is an hour. I have yet to see one where the fox isn't found within the hour, typically about half that, and in many cases the fox only transmits for 30 seconds every 5 minutes or something, just to make it harder.
I'll say your sentiment is mostly correct, but it probably wasn't a matter of minutes. To use an existing DF setup on 315 MHz means changing your LO (local oscillator, aka your frequency source) and filters at a minimum. If you're using a digital/programmable oscillator, then changing the LO is easy. If you're using a fixed analog oscillator then you are probably ordering one because no ham has a 315 MHz crystal lying around.
Any well designed DF is going to have filters to improve the signal, and even a single pole 440 MHz high-pass or band-pass filter will reject nearly everything at 315 MHz. If the DF is SDR based it may be using digital filtering, but it's far more likely to have analog filters, so you would either need to buy or build new filters. Buying filters that you'll probably never use again seems like a waste, so they probably would wind their own inductors by hand and solder the components themselves, which puts the filter price in the $1 range instead of the $100 range.
Even then, your 440 MHz antennas are poorly tuned at 315 MHz so any self respecting ham would have built some new ones out of a coat hanger at minimum.
So it probably would take at least one day for an experienced and motivated ham to make their existing DF equipment into a workable solution.
Any well designed DF is going to have filters to improve the signal, and even a single pole 440 MHz high-pass or band-pass filter will reject nearly everything at 315 MHz. If the DF is SDR based it may be using digital filtering, but it's far more likely to have analog filters, so you would either need to buy or build new filters. Buying filters that you'll probably never use again seems like a waste, so they probably would wind their own inductors by hand and solder the components themselves, which puts the filter price in the $1 range instead of the $100 range.
Even then, your 440 MHz antennas are poorly tuned at 315 MHz so any self respecting ham would have built some new ones out of a coat hanger at minimum.
So it probably would take at least one day for an experienced and motivated ham to make their existing DF equipment into a workable solution.
Yes and no. I usually use the body-shielding technique: Attenuate or reduce gain until the signal is faint. Hold the receiver against my chest and turn in a slow circle until it disappears entirely. Now I know the transmitter is behind me. It's crude, but expedient, and fairly effective.
This has the advantage of working with any receiver type, any antenna (it's actually particularly good with the otherwise-useless rubber-duck that cheap HTs ship with), and any signal with a wavelength longer than my torso is wide, -ish. It falls off gracefully at the limit there.
Would better gear produce better results? Sure, you'd almost certainly beat me to the fox if you had that stuff sitting around. But I'll be knocking on the guy's door while you're still soldering.
Incidentally, anyone who's been playing with TPMS decoding probably has a 315MHz-specific filter kit sitting around. It works okay-ish without that, but it gets truly creepy when given a good filter and antenna. SAW cans for 315 and 433 are about $4/ea.
This has the advantage of working with any receiver type, any antenna (it's actually particularly good with the otherwise-useless rubber-duck that cheap HTs ship with), and any signal with a wavelength longer than my torso is wide, -ish. It falls off gracefully at the limit there.
Would better gear produce better results? Sure, you'd almost certainly beat me to the fox if you had that stuff sitting around. But I'll be knocking on the guy's door while you're still soldering.
Incidentally, anyone who's been playing with TPMS decoding probably has a 315MHz-specific filter kit sitting around. It works okay-ish without that, but it gets truly creepy when given a good filter and antenna. SAW cans for 315 and 433 are about $4/ea.
I concede. Some people could have found this guy in a few minutes :)
I may have fallen into this trap: https://xkcd.com/974/
I may have fallen into this trap: https://xkcd.com/974/
> Was it difficult to find the exact source, or not? Is there some reason that getting directionality on a constant 315 MHz signal is harder than one would think?
Physically, it's easier to find a UHF beacon (315 MHz is considered ultra high frequency) than it is to find a lower frequency beacon (lots of direction finding contests are done on VHF and HF). The higher frequency means a shorter wavelength and better phase (direction) resolution with a smaller aperture (distance between antennas).
However, many (most) hams don't have equipment that covers 315 MHz. UHF isn't popular because it is shorter range and more expensive equipment (you can build HF equipment with much simpler components, and the design is less complex). Plus, 315 MHz isn't in one of the ham bands, so ham direction finding equipment probably won't be designed for it even if it is UHF.
A wide band SDR would include 315 MHz. While there are many younger hams that enjoy cheap SDRs like the RTL-SDR, many of the older, grumpier hams see it as dangerous and letting undisciplined "hackers" into their hobby. To build a direction finder with an SDR you either need to have an expensive multi-channel SDR (I have a Lime SDR that would work), or you need to construct your own mixer to feed a single channel SDR, or you need to wire up two RTL-SDRs with a coherent clock signal, which puts this out of the range of your "common hacker." Here are two ways you could do this on the cheap: https://www.rtl-sdr.com/building-a-passive-radar-system-with... https://www.rtl-sdr.com/building-a-direction-finding-system-...
So while most armchair HN readers would love to tell you about how easy this is, most people don't have the equipment sitting around to do direction finding on a 315 MHz signal. The best most people could do would be to "wardrive" around the neighborhood and look for where the signal strength peaks, but this will really only narrow it down to a few houses and then you need to start knocking on doors. A good direction finding setup would pinpoint the exact house.
Source: I'm a ham (recently made extra), but no, I won't tell you my callsign to prove it.
Physically, it's easier to find a UHF beacon (315 MHz is considered ultra high frequency) than it is to find a lower frequency beacon (lots of direction finding contests are done on VHF and HF). The higher frequency means a shorter wavelength and better phase (direction) resolution with a smaller aperture (distance between antennas).
However, many (most) hams don't have equipment that covers 315 MHz. UHF isn't popular because it is shorter range and more expensive equipment (you can build HF equipment with much simpler components, and the design is less complex). Plus, 315 MHz isn't in one of the ham bands, so ham direction finding equipment probably won't be designed for it even if it is UHF.
A wide band SDR would include 315 MHz. While there are many younger hams that enjoy cheap SDRs like the RTL-SDR, many of the older, grumpier hams see it as dangerous and letting undisciplined "hackers" into their hobby. To build a direction finder with an SDR you either need to have an expensive multi-channel SDR (I have a Lime SDR that would work), or you need to construct your own mixer to feed a single channel SDR, or you need to wire up two RTL-SDRs with a coherent clock signal, which puts this out of the range of your "common hacker." Here are two ways you could do this on the cheap: https://www.rtl-sdr.com/building-a-passive-radar-system-with... https://www.rtl-sdr.com/building-a-direction-finding-system-...
So while most armchair HN readers would love to tell you about how easy this is, most people don't have the equipment sitting around to do direction finding on a 315 MHz signal. The best most people could do would be to "wardrive" around the neighborhood and look for where the signal strength peaks, but this will really only narrow it down to a few houses and then you need to start knocking on doors. A good direction finding setup would pinpoint the exact house.
Source: I'm a ham (recently made extra), but no, I won't tell you my callsign to prove it.
Couldn't you just walk around with a laptop and an RTL-SDR device and measure how strong the (near 315MHz) signal is at various locations as you move about?
That's what I meant when I said "wardrive" around the neighborhood and look for where the signal strength peaks. It's easy in theory, but I'd guess you'd probably only narrow it down to plus/minus two houses in every direction- UHF attenuates through walls, but in air it is more gradual, and so you wouldn't get a sharp peak as you walk around. So now you have eight houses to go check. But once you started knocking, probably all the neighbors would either say, "yeah, that's probably Bill, he's does electronic stuff" or maybe they would say, "that's might be my neighbor I've never met."
A strong directional antenna would help, but that means that you have to build it yourself, I'm not aware of an off the shelf antenna that has high gain at 315 MHz. So
A strong directional antenna would help, but that means that you have to build it yourself, I'm not aware of an off the shelf antenna that has high gain at 315 MHz. So
There's a new piece of inexpensive gear for RDF:
KerberosSDR.
It's a quad input coherent radio receiver based after the RTL-SDR chips. One such function is it can give direction and strength of signals in a wide area.
And I find this electronic kit antenna works well as long as you pull it out for the appropriate frequency: https://www.nooelec.com/store/ratlsnake-m5.html
I use 4 of these for my KerberosSDR.
KerberosSDR.
It's a quad input coherent radio receiver based after the RTL-SDR chips. One such function is it can give direction and strength of signals in a wide area.
And I find this electronic kit antenna works well as long as you pull it out for the appropriate frequency: https://www.nooelec.com/store/ratlsnake-m5.html
I use 4 of these for my KerberosSDR.
I saw that these are shipping and have almost convinced myself to buy one. I think they're pretty neat and now a wideband phased-array direction finder is a project that a smart high-schooler can do, at a price point that many people can reach. Maybe the next time this type of interference occurs the headline will read different: "Local kid solves problem with science fair project, stumped adults for weeks."
With that said, these KerberosSDRs (or any multi-channel coherent SDR solution) are not widespread, are considerably more expensive (6-7x more than a single RTL-SDR), and are only recently available. So my previous point still stands about how armchair hackers can talk about how easy this problem is to solve in theory but they lack the actual equipment to do it.
With that said, these KerberosSDRs (or any multi-channel coherent SDR solution) are not widespread, are considerably more expensive (6-7x more than a single RTL-SDR), and are only recently available. So my previous point still stands about how armchair hackers can talk about how easy this problem is to solve in theory but they lack the actual equipment to do it.
Oh absolutely. A simple RTL-SDR is widespread, but anything coherent is absolutely not. I mean, the Ettus 4x4 pcie card is coherent, but it's also starting at $5000 for the card. And since it's a pcie, it goes in a very non-portable computer.
The KerberosSDR has one very significant disadvantage: the databus is usb2. The theoretical max is 30M samples at 8bit I and Q... And frankly we need much more bandwidth. But for a beginner foray into coherent radio applications, a KerberosSDR for $100~ is crazy worth it.
Now, the older way of doing RDF (I'm a Ham, btw), was to get a handheld receiver capable of listening to the freq in question, highly directional antenna, take measurements and move. Effectively, the human with a receiver is the manual triangulator which can be trained with experience. That was because gear that did triangulation was $$$$$$.
The KerberosSDR has one very significant disadvantage: the databus is usb2. The theoretical max is 30M samples at 8bit I and Q... And frankly we need much more bandwidth. But for a beginner foray into coherent radio applications, a KerberosSDR for $100~ is crazy worth it.
Now, the older way of doing RDF (I'm a Ham, btw), was to get a handheld receiver capable of listening to the freq in question, highly directional antenna, take measurements and move. Effectively, the human with a receiver is the manual triangulator which can be trained with experience. That was because gear that did triangulation was $$$$$$.
In the context of this article, having eight houses to check is soooo much better than having absolutely no clue. If it's not a malicious actor, you'll find out what's emitting the signal in a matter of an hour tops. Being able to do that using a $10 device from ebay is fantastic.
Ok, you have 8 houses to check. What do you do now?
You knock, explain the problem, ask if they've installed new electronics lately, especially remote controlled/domotics stuff. Repeat until you get a satisfactory answer. Chances that you will get one are very high.
The article says it took a few weeks. I don't think the worth of this article boils down to whether it was a "hard" problem or not, just that an unexpected device caused unexpected problems.
The article is representative of the modern fad of mixing narrative story telling with information. It could be half as long and still provide sufficient "color" to prevent it being merely a bullet list of facts.
This isn't a modern fad, it's literally the point of storytelling.
Point is, reporting should not involve storytelling at all.
This type of reporting is called a "feature story", as opposed to "straight news" or "hard news". The whole point of a feature is to tell an interesting but not necessarily time-sensitive story about something which happened.
https://en.m.wikipedia.org/wiki/Feature_story
https://en.m.wikipedia.org/wiki/Feature_story
Sure. I'm just tired of all news being of this kind (or long-form writing). I can't find any news sources optimized for communicating facts and facts only, as efficiently as possible.
All news is not like this. In fact, most news is not like this. I am not sure where you are getting your news from?
When reading/writing news, "news stories" are one option as seen here, and "news reports" are another option. I think so long as there's a group of people who prefer the story format, better to offer that format than leave those people disinterested in consuming news.
I wonder if they realize they're leaving the other group disinterested in consuming news.
I don't read news anymore. Haven't for years. Initially it was because I found it too depressing, later on I realized that a) almost nothing on the news is meaningful to my life and b) it's mostly full of bullshit designed to grab eyeballs, but recently I realized yet another motivation: I don't read news because of the narrative style. I'd probably read some if I could find a source that actually cared about inverted pyramid, and ideally just made the story a list of bullet points. Having to burn brain cycles to tease out actual facts from someone's storytelling is just a waste of time to me.
I don't read news anymore. Haven't for years. Initially it was because I found it too depressing, later on I realized that a) almost nothing on the news is meaningful to my life and b) it's mostly full of bullshit designed to grab eyeballs, but recently I realized yet another motivation: I don't read news because of the narrative style. I'd probably read some if I could find a source that actually cared about inverted pyramid, and ideally just made the story a list of bullet points. Having to burn brain cycles to tease out actual facts from someone's storytelling is just a waste of time to me.
What are the odds that they were following one of those "How to build a do-it-yourself radio transmitter using JUST a raspberry pi!" articles?
https://www.rtl-sdr.com/transmitting-fm-am-ssb-sstv-and-fsq-...
https://www.rtl-sdr.com/transmitting-fm-am-ssb-sstv-and-fsq-...
Oh no, I remember this. The Pi's output pin causes harmonics so the consequences would be so bad. Every article, including this one, that talks about using the Pi to transmit specifically screams about using a band-pass filter.
I'd love to see a screenshot of a spectrum-analyzer when the device is running nearby.
I'd love to see a screenshot of a spectrum-analyzer when the device is running nearby.
What this summary misses is the non-trivial difficulty in finding such a device. Fox hunting is hard, particularly if you don't know the frequency.
And this, everyone, is why the FCC regulation of transmitter hardware is a good thing and a benefit to society.
And yet it's absurd when, to follow the law, you need to do testing on even unintentional radiators (with few exceptions) with a digital clock higher than 9 kHz (yes, kilo Hertz...)
I leave it up to you to guess what percentage of low-volume devices are actually tested, but I'm pretty sure "design it sensibly and we'll take the business risk that we're not going to get found and hosed by the FCC" is wildly more common than non-technical people would assume. For devices released in under quantity of 10K units, I bet the percentage of digital devices without intentional transmitters that are certified rounds to 0%. (Arduino was only FCC certified on the 5th version, IIRC.)
I leave it up to you to guess what percentage of low-volume devices are actually tested, but I'm pretty sure "design it sensibly and we'll take the business risk that we're not going to get found and hosed by the FCC" is wildly more common than non-technical people would assume. For devices released in under quantity of 10K units, I bet the percentage of digital devices without intentional transmitters that are certified rounds to 0%. (Arduino was only FCC certified on the 5th version, IIRC.)
> And yet it's absurd when, to follow the law, you need to do testing on even unintentional radiators (with few exceptions) with a digital clock higher than 9 kHz (yes, kilo Hertz...)
And the answer to "why 9 kHz?" is pretty obvious from: https://www.ntia.doc.gov/files/ntia/publications/2003-alloch...
Or do you think those "RadioNavigation" users magically don't care about interference?
And the answer to "why 9 kHz?" is pretty obvious from: https://www.ntia.doc.gov/files/ntia/publications/2003-alloch...
Or do you think those "RadioNavigation" users magically don't care about interference?
This is a situation where the law and the actual practice is so diverged that we've basically just enshrined selective prosecution by the FCC.
Small volume manufacturers just try to design well and roll the dice because (almost?) no one is spending four figures on an accredited lab to do emissions testing on a device that sells a few dozen or couple hundred units per year.
Some try to find a way to indicate that it's used only in transportation, that it's industrial/commercial test equipment, that it's a peripheral device or sub-assembly and not a finished end-user device, others just realize that the FCC isn't going to bust down anyone's door because a device not emitting harmful RF doesn't have a testing certificate on file.
Small volume manufacturers just try to design well and roll the dice because (almost?) no one is spending four figures on an accredited lab to do emissions testing on a device that sells a few dozen or couple hundred units per year.
Some try to find a way to indicate that it's used only in transportation, that it's industrial/commercial test equipment, that it's a peripheral device or sub-assembly and not a finished end-user device, others just realize that the FCC isn't going to bust down anyone's door because a device not emitting harmful RF doesn't have a testing certificate on file.
His transmitter hardware was probably fine even if it was some $2 module direct from China (which it probably was), but he was transmitting constantly in a band designated for short intermittent or periodic signals and very low power.
In this case, the transmitter was likely legal, and an FCC certified unit, it was just not complying with the rules as such for that band.
https://linxtechnologies.com/wp/wp-content/uploads/fcc_resou...
https://linxtechnologies.com/wp/wp-content/uploads/fcc_resou...
I would be fairly shocked if it turned out to be an FCC certified transmitter. (That's not to say I don't agree the primary issue was a duty cycle violation, but very few of the hobbyist modules on the market are FCC certified.)
How's that work anyway? I thought their certification on transmitters was meant to certify that the design didn't emit any extra RF noise other than that it was intended to, that the power of the generated signal was commensurate with its' intended use, and that it fell within a frequency band that wasn't reserved for something else.
The only thing that really chafes for me with the FCC is their absolute retardation with Internet regulation, and I'm still not sure I'm 100% okay with idea of "spectrum auctions". I get the idea behind it, but I seriously question the wisdom of anything that basically self-selects for corporate ownership over anyone else.
Still a bit of a noob on the RF scene though, so I've probably got nil real insight into the real reason the FCC is actually doing a good job.
The only thing that really chafes for me with the FCC is their absolute retardation with Internet regulation, and I'm still not sure I'm 100% okay with idea of "spectrum auctions". I get the idea behind it, but I seriously question the wisdom of anything that basically self-selects for corporate ownership over anyone else.
Still a bit of a noob on the RF scene though, so I've probably got nil real insight into the real reason the FCC is actually doing a good job.
I don't know much about RF, but essentially any device can act as a software defined radio.. loops, obviously, operate many times per second; if you use that loop to send power down a wire, you get software defined transmission.
If your power is going down a long wire, it tends to generally get better travel on the signal (for accidental transmitters, intentionally sending signals can can use math and design to better results)
So if your Arduino operates on a loop, and sends LOW voltage, and occassionally HIGH voltage, you get a radio. The frequency is not exactly always the loops executed per second, it tends to get mirrored onto many frequencies for some reason I'm not familiar with.. you can force it to a certain frequency by getting you loop to operate at a specific speed, but it will also appear in other frequencies.
Would love a radio guy to expand on my explanation here.
If your power is going down a long wire, it tends to generally get better travel on the signal (for accidental transmitters, intentionally sending signals can can use math and design to better results)
So if your Arduino operates on a loop, and sends LOW voltage, and occassionally HIGH voltage, you get a radio. The frequency is not exactly always the loops executed per second, it tends to get mirrored onto many frequencies for some reason I'm not familiar with.. you can force it to a certain frequency by getting you loop to operate at a specific speed, but it will also appear in other frequencies.
Would love a radio guy to expand on my explanation here.
> tends to get mirrored onto many frequencies for some reason I'm not familiar with.
Play with this for a few minutes: http://www.jezzamon.com/fourier/index.html
And watch any of these: https://www.youtube.com/results?search_query=vibrating+reed+...
Okay, so think of a radio receiver as being sensitive to a particular frequency, because it has a filter in front of it. A vibrating reed of a specific length, if you will. (This is almost exactly true for certain types of crystal and SAW filters, actually.)
But when you flip a digital output from 0 to 1 or vice-versa, it changes state very quickly -- the output is essentially a square wave. (Physical limits mean it does have a finite slew rate...) Which means it contains components of every frequency. Think of coming up to one of those vibrating-reed meters and smacking it -- a single impulse excites ALL the reeds.
Smack it regularly (change the pin state at a specific frequency) and the reeds that're way off frequency will just sort of bounce around but not be particularly excited. You're creating noise, but it's just noise. But the reeds that're odd multiples of the smacking frequency will vibrate too -- these are the harmonics. They'll get really excited, almost as excited as the fundamental. (The evens essentially cancel out.)
Here's what it looks like on the radio spectrum: https://www.youtube.com/watch?v=eC36AqL5mw8
Incidentally, this is why so many chips now boast "slew-rate limited" outputs: to intentionally slow down those transitions, to reduce the amount of noise that has to be filtered and shielded in order for the device to pass RF emissions testing.
Play with this for a few minutes: http://www.jezzamon.com/fourier/index.html
And watch any of these: https://www.youtube.com/results?search_query=vibrating+reed+...
Okay, so think of a radio receiver as being sensitive to a particular frequency, because it has a filter in front of it. A vibrating reed of a specific length, if you will. (This is almost exactly true for certain types of crystal and SAW filters, actually.)
But when you flip a digital output from 0 to 1 or vice-versa, it changes state very quickly -- the output is essentially a square wave. (Physical limits mean it does have a finite slew rate...) Which means it contains components of every frequency. Think of coming up to one of those vibrating-reed meters and smacking it -- a single impulse excites ALL the reeds.
Smack it regularly (change the pin state at a specific frequency) and the reeds that're way off frequency will just sort of bounce around but not be particularly excited. You're creating noise, but it's just noise. But the reeds that're odd multiples of the smacking frequency will vibrate too -- these are the harmonics. They'll get really excited, almost as excited as the fundamental. (The evens essentially cancel out.)
Here's what it looks like on the radio spectrum: https://www.youtube.com/watch?v=eC36AqL5mw8
Incidentally, this is why so many chips now boast "slew-rate limited" outputs: to intentionally slow down those transitions, to reduce the amount of noise that has to be filtered and shielded in order for the device to pass RF emissions testing.
Perhaps you could spend a few moments thinking of a creative way to express your thought without the casually offensive language.
It's not a "mystery frequency", the frequency is perfectly obvious, 315 MHz. It was a "mystery transmitter" stomping on the frequency, that's all.
Not just the title; "the overpowering frequency persisted" and "how a strong frequency can derail a weak frequency" should each be "transmission" or "signal."
It was a mystery until they discovered what the frequency was.
But if your 315 MHz devices aren't working, it's probably interference on 315 MHz causing the problem.
And if it took weeks for someone to look up the FCC ID printed on literally every single device affected by this problem, and learn what frequency it operates on, then I think that suggests a deeper problem.
And if it took weeks for someone to look up the FCC ID printed on literally every single device affected by this problem, and learn what frequency it operates on, then I think that suggests a deeper problem.
The article misses to point out an important insight that this could be illegal and FCC governs radio spectrum. You can't just spin up a giant transmitter as a DIY project, you'll need a Ham radio license and can only operate in a certain frequency.
Lazy article - readers now think "hah...some nerd in his basement, no big deal." except that it is a federal crime.
Lazy article - readers now think "hah...some nerd in his basement, no big deal." except that it is a federal crime.
That's not accurate. You absolutely can spin up a transmitter as a DIY project, as long as you stay within the power and duty cycle limits. Devices not intended for eventual sale don't even have to be tested or certified, as long as the builder/user makes a good-faith effort to comply with the regulations.
A ham license moves you into a different set of limits and gives you more bands to play in, that's all.
Take a read of https://www.ti.com/lit/an/swra048/swra048.pdf for a reasonably cogent summary of the regulations. The FCC's own rules are considerably denser legalese, and the relevant parts are scattered over hundred of pages. That app note brings it all together.
More: https://transition.fcc.gov/Bureaus/Engineering_Technology/Do... (See the "Home-built transmitters that are not for sale" section.)
A ham license moves you into a different set of limits and gives you more bands to play in, that's all.
Take a read of https://www.ti.com/lit/an/swra048/swra048.pdf for a reasonably cogent summary of the regulations. The FCC's own rules are considerably denser legalese, and the relevant parts are scattered over hundred of pages. That app note brings it all together.
More: https://transition.fcc.gov/Bureaus/Engineering_Technology/Do... (See the "Home-built transmitters that are not for sale" section.)
You're probably correct as I do not have any background in Radio. My point was simply that this article should have mentioned something related to radio frequencies and how it is regulated. It does disservice by telling readers nothing about regulations. This is terrible journalism.
That TI document is a nice look at the regulations that concern the device designer. There are also some regulations that the device user needs to comply with that you don't automatically get for free by using a compliant device. I didn't see those in the TI document, but may have missed them.
Probably the most important are for interacting with other services that share that band. A band might have several services authorized to use it, and these services have different priorities in case of conflict.
Generally, the rule is if a higher priority service interferes with you, it is up to you to filter it out or tolerate it. If you interfere with a higher priority service, it is up to you to stop.
For example, the lower part of the 2.4 GHz WiFi band overlaps the higher part of the 13 cm ham band. Hams have higher priority. So if I were to use that band for some long range telemetry (I have an Extra class ham license) and that messes with you using the lower WiFi channels, you are the one who has to find a workaround. If your WiFi messes up my telemetry, you are again the one who has to find a workaround.
On the other hand, part of 13 cm is an Industrial, Scientific, and Medical (ISM) band. That ISM band has higher priority than the ham band. If your microwave oven messes up my telemetry, I'm the one who has to cope, because microwave ovens are classified as and operated as ISM devices. And if my telemetry messes up cooking your burrito, I'm the one who has to deal with it.
Probably the most important are for interacting with other services that share that band. A band might have several services authorized to use it, and these services have different priorities in case of conflict.
Generally, the rule is if a higher priority service interferes with you, it is up to you to filter it out or tolerate it. If you interfere with a higher priority service, it is up to you to stop.
For example, the lower part of the 2.4 GHz WiFi band overlaps the higher part of the 13 cm ham band. Hams have higher priority. So if I were to use that band for some long range telemetry (I have an Extra class ham license) and that messes with you using the lower WiFi channels, you are the one who has to find a workaround. If your WiFi messes up my telemetry, you are again the one who has to find a workaround.
On the other hand, part of 13 cm is an Industrial, Scientific, and Medical (ISM) band. That ISM band has higher priority than the ham band. If your microwave oven messes up my telemetry, I'm the one who has to cope, because microwave ovens are classified as and operated as ISM devices. And if my telemetry messes up cooking your burrito, I'm the one who has to deal with it.
We'd all be impressed and terrified if your telemetry "messed up" a burrito, whether it was in the microwave oven or out.
Yeah its pursuable as a crime but there was no malicious intent and it doesnt make sense to charge anyone. Im actually super glad they used good judgement.
True, but what both the article and you miss out on is that some radio frequencies are unlicensed.
You actually can spin up a transmitter as a DIY projected, and even built exactly what this guy did, as long as you use check up your domestic laws and ensure you're using the right frequencies and in the manners prescribed.
Specifically, see the ITU recommendations on 315 Mhz for low powered transmitters. You should be good if you don't exceed 10 mW.
[0]: https://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-SM.2153-2-20...
You actually can spin up a transmitter as a DIY projected, and even built exactly what this guy did, as long as you use check up your domestic laws and ensure you're using the right frequencies and in the manners prescribed.
Specifically, see the ITU recommendations on 315 Mhz for low powered transmitters. You should be good if you don't exceed 10 mW.
[0]: https://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-SM.2153-2-20...
Under FCC jurisdiction at least, 315 MHz has strict duty cycle limits -- you can't transmit more than two seconds per hour. There's a really good summary here: https://www.ti.com/lit/an/swra048/swra048.pdf
So, yes, you can buy exactly the parts this guy did, and implement the project differently, and be completely legal.
But he implemented it such that the duty cycle violated regulations, and here we see why the duty cycle is supposed to be very limited. What he did was in clear violation, and he did not need fancy test equipment to determine that.
So, yes, you can buy exactly the parts this guy did, and implement the project differently, and be completely legal.
But he implemented it such that the duty cycle violated regulations, and here we see why the duty cycle is supposed to be very limited. What he did was in clear violation, and he did not need fancy test equipment to determine that.
Even though he inadvertently caused consternation with people with keyfobs and rc garage doors, he did quit after it was brought to his attention. I'm much much more lenient on someone who's tinkering and causes that accidentally.
And if you read into the article, the person who did it was special needs (mentally or physically). They're also likely on a fixed income. Jail would be unconscionable, as would fining someone which lack of payment would lead to jail.
Hopefully the result here is "person quits, person reads up on proper RF practice, and does things better next time"
And if you read into the article, the person who did it was special needs (mentally or physically). They're also likely on a fixed income. Jail would be unconscionable, as would fining someone which lack of payment would lead to jail.
Hopefully the result here is "person quits, person reads up on proper RF practice, and does things better next time"
People seem to love these stories even though there's always a boring explanation.
1. Car key fobs aren't working... Mystery! Conspiracy!
2. ... one week goes by ...
3. Oh, actually something was broken / someone was doing something stupid.
e.x. https://news.ycombinator.com/item?id=19046475 cause: "faulty consumer electronic equipment stuck in transmit mode" https://calgary.ctvnews.ca/carstairs-co-op-determines-source...
At least "homemade battery-operated device designed by a local resident" is slightly more interesting.
1. Car key fobs aren't working... Mystery! Conspiracy!
2. ... one week goes by ...
3. Oh, actually something was broken / someone was doing something stupid.
e.x. https://news.ycombinator.com/item?id=19046475 cause: "faulty consumer electronic equipment stuck in transmit mode" https://calgary.ctvnews.ca/carstairs-co-op-determines-source...
At least "homemade battery-operated device designed by a local resident" is slightly more interesting.
On a related note: LED light bulbs often emit radio frequencies and all of the ones I’ve tried so far interfere with my garage door. Which was insanely hard to figure out.
(Garage door openers have spots for 2 light bulbs.)
(Garage door openers have spots for 2 light bulbs.)
What would happen if you just jammed car doors across an entire city? Or after a big game/concert? Could cause some panic i think.
Most (all?) cars have a keyed driver door. Otherwise you couldn't get into the vehicle if the battery died.
Sure, but if your car was working perfectly fine on the way in to the game and three hours later hundreds of people can't get into their cars either...you're thinking the bomb is coming.
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