"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?
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.
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.
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.
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.
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.
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 may have fallen into this trap: https://xkcd.com/974/
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.
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
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.
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.
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 $$$$$$.
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.