
Mystery Frequency Disrupted Car Fobs in an Ohio City, and Now Residents Know Why - wglb
https://www.nytimes.com/2019/05/04/us/key-fobs-north-olmsted-ohio.html
======
nkurz
The answer (excerpted from the linked article):

    
    
      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.

~~~
colanderman
FYI: quoting material like that is impossible to read on mobile because it
does not wrap. Please just use ">" as an quotation marker.

~~~
nkurz
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.

~~~
Normal_gaussian
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.

~~~
giancarlostoro
On the other hand reader mode for FireFox temporarily fixes the bug.

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

~~~
ComputerGuru
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.

~~~
notatoad
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".

------
ajross
And this, everyone, is why the FCC regulation of transmitter hardware is a
good thing and a benefit to society.

~~~
salawat
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.

~~~
ldoughty
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.

~~~
myself248
> 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](http://www.jezzamon.com/fourier/index.html)

And watch any of these:
[https://www.youtube.com/results?search_query=vibrating+reed+...](https://www.youtube.com/results?search_query=vibrating+reed+frequency+meter)

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](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.

------
myself248
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.

~~~
wglb
It was a mystery until they discovered what the frequency was.

~~~
myself248
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.

------
spectramax
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.

~~~
myself248
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](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...](https://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet63/oet63rev.pdf)
(See the "Home-built transmitters that are not for sale" section.)

~~~
tzs
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.

~~~
jessaustin
We'd all be impressed and terrified if your telemetry "messed up" a burrito,
whether it was in the microwave oven or out.

------
tlrobinson
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](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...](https://calgary.ctvnews.ca/carstairs-co-op-determines-source-of-
interference-that-rendered-vehicle-key-fobs-inoperable-1.4279460)

At least "homemade battery-operated device designed by a local resident" is
slightly more interesting.

------
gonyea
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.)

------
jcims
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.

~~~
Evidlo
Most (all?) cars have a keyed driver door. Otherwise you couldn't get into the
vehicle if the battery died.

~~~
jcims
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.

