Re:You block ads in your browser, why not in your city?
by matheusmoreira on Sunday December 26, 2021 @05:10PM
(#29696870)
> Each car radio sends out a signal at a frequency higher than the one it is receiving from the radio station.
Why would it do that? I thought car radios were merely receivers, not transmitters. This is insane...
Re:You block ads in your browser, why not in your city?
by xyzzyz on Sunday December 26, 2021 @05:58PM
(#29697186)
It is a result of the mechanism used for operation. See https://en.m.wikipedia.org/wiki/Superheterodyne_receiver especially the section on Local oscillator radiation
Re:You block ads in your browser, why not in your city?
by dmm10 on Tuesday December 28, 2021 @03:13PM
(#29717523)
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.
Re:You block ads in your browser, why not in your city?
by gruturo on Monday December 27, 2021 @08:38AM
(#29702395)
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.
Re:You block ads in your browser, why not in your city?
by heavyset_go on Sunday December 26, 2021 @11:58PM
(#29699440)
Check this out: https://scholarsmine.mst.edu/cgi/viewcontent.cgi?referer=&ht...
> 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.
[1] https://web.archive.org/web/20020720075012/http://www.mobilt...