There’s no transmitter.
There’s a GPS receiver in your car infotainment unit or mobile phone which works out where you are by measuring the exact timing of radio signals from satellites. The infotainment unit or your phone has maps already downloades.
These are a free service provided by governments:
* GPS – U.S.A.
* Galileo – Europe
* Glonass – Russia
* BeiDou – China
Most built-in car units need you to buy new maps every year. Some dedicated units like Garmin and TomTom have free map updates, some don’t.
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