I have been studying how radio signals work lately trying to get my ham radio license. I then realized that phone calls and texts are essentially radio signals. What sort of signal are they? What frequencies do cell phones calls operate on? Is there a way to intercept and decode sms text messages using some sort of reciever? How are they encoded and decoded? This is just for hypothetical reasons. I have no interest in trying to intercept phone calls or anything.
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Up to about thirty years ago it was all very simple. The phones were essentially walkie-talkies with a microprocessor to automatically tune them to the right frequency on command from a tower. They used ordinary narrow band FM modulated signals.
Since then the systems have [gradually evolved](https://en.wikipedia.org/wiki/Comparison_of_mobile_phone_standards) to great complexity. The modulation, encoding, data transmission protocols are all quite elaborate, and the books describing them are thousands of pages long. It would take a motivated effort to learn and to understand how exactly any particular standard is implemented. Needless to say, modern systems are built with data protection in mind, and casual eavesdropping is not possible.
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