> they prototyped roadside billboards thay could infer what radio stations the cars driving by were listening to
Any idea how this was supposed to work? I don't know how that information would leak out unless it was just listening for the audio from a car with windows rolled down.
An archive of the company behind that tech [1], has this to say:
> Each car radio sends out a signal at a frequency higher than the one it is receiving from the radio station. When a car passes by one of the MobilTrak sensors, the sensor picks up on the signal to determine what the driver is listening to on the radio
And US6813475B1 seems to be the patent behind the tech.
If they ever really could find that sort of signal in the noise of the real world, I've got to imagine that improved tech for in-car radios, not to mention people listening to their phones via Bluetooth and SiriusXM, has rendered it even more broken.
Most radio receivers transmit a very weak signal slightly higher than the carrier frequency of the station tuned as a result of how they enhance received signals. Look up superheterodyne for details.
It's a side effect of how tuning works (local oscillator), and the signal is extremely weak, very little of it radiates out due to some components / PCB traces behaving as an accidental (poor) antenna.
Still, with good enough equipment it can be detected even from some distance.
Any idea how this was supposed to work? I don't know how that information would leak out unless it was just listening for the audio from a car with windows rolled down.