11 ms·

Cutting thru the clickbait: Someone built a homemade light control system that operated at 315Mhz, and caused interference with many other devices.

by robbyt 7y ago

pridkett 7y ago
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.
- nkurz 7y ago
  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?
  - danso 7y ago
    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.
  - myself248 7y ago
    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.
    - throw20102010 7y ago
      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.
      - myself248 7y ago
        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.
  - mikestew 7y ago
    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.
    - riskable 7y ago
      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.
      - toyg 7y ago
        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.
      - megaremote 7y ago
        Car manufacturers: Is it killing more than a 1000 people? Nah, we don't care.
  - throw20102010 7y ago
    > 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-an-rtl-sdr/ https://www.rtl-sdr.com/building-a-passive-radar-system-with... https://www.rtl-sdr.com/building-a-direction-finding-system-with-a-frequency-mixer-sdr/ 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.
    - riskable 7y ago
      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?
- sidlls 7y ago
  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.
  - danso 7y ago
    This isn't a modern fad, it's literally the point of storytelling.
    - TeMPOraL 7y ago
      Point is, reporting should not involve storytelling at all.
      - hunter2_ 7y ago
        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.
        TeMPOraL 7y ago
        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.
      - andrewem 7y ago
        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
jjoonathan 7y ago
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-with-just-a-raspberry-pi/ https://www.rtl-sdr.com/transmitting-fm-am-ssb-sstv-and-fsq-...
- amingilani 7y ago
  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.
ComputerGuru 7y ago
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.
- driverdan 7y ago
  The title is 100% clickbait. I refuse to read content with clickbait titles so thank you OP for the summary.
- notatoad 7y ago
  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".
wglb 7y ago
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.

Cutting thru the clickbait: Someone built a homemade light control system that operated at 315Mhz, and caused interference with many other devices.

by robbyt 7y ago

Cutting thru the clickbait: Someone built a homemade light control system that operated at 315Mhz, and caused interference with many other devices.

pridkett 7y ago

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.

nkurz 7y ago
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?
- danso 7y ago
  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.
- myself248 7y ago
  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.
  - throw20102010 7y ago
    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.
    - myself248 7y ago
      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.
- mikestew 7y ago
  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.
  - riskable 7y ago
    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.
    - toyg 7y ago
      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.
    - megaremote 7y ago
      Car manufacturers: Is it killing more than a 1000 people? Nah, we don't care.
- throw20102010 7y ago
  > 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-an-rtl-sdr/ https://www.rtl-sdr.com/building-a-passive-radar-system-with... https://www.rtl-sdr.com/building-a-direction-finding-system-with-a-frequency-mixer-sdr/ 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.
  - riskable 7y ago
    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?
sidlls 7y ago
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.
- danso 7y ago
  This isn't a modern fad, it's literally the point of storytelling.
  - TeMPOraL 7y ago
    Point is, reporting should not involve storytelling at all.
    - hunter2_ 7y ago
      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.
      - TeMPOraL 7y ago
        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.
    - andrewem 7y ago
      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

jjoonathan 7y ago

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-with-just-a-raspberry-pi/ https://www.rtl-sdr.com/transmitting-fm-am-ssb-sstv-and-fsq-...

amingilani 7y ago
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.

ComputerGuru 7y ago

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.

driverdan 7y ago
The title is 100% clickbait. I refuse to read content with clickbait titles so thank you OP for the summary.
notatoad 7y ago
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".

wglb 7y ago

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.