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Mobile Phone Detector

Mike McKean
Hi,

If anyone can help me, or explain this, I'd appreciate it. I normally like to understand what I am doing, but on this occasion, I just don't. But I found several different Youtuibes and Diagrams that all used trhe same I.C. But it just does not make sense to me.


I am building a mobile phone detector. I have ordered some parts, based on some web-based reserach I have done. So too late to change. But the parts cost pennies so it's just my time I am potentially wasting.


If mobile phones operate at about 0.8 GHZ to 3.4 GHZ, then I'd expect to build soemthing with a receiver that is a tuned circuit, or several different tuned circuits, but operating at those frequencies. But the I.C. everyone seems to be using is the LM386, which is an audio amp?  I just don't understand it?


I want to detect a mobile phone in "idle", i.e. even when it is not actively mbeing used.


I attached my roiugh working notes which include a couple jpeg diagrams that I am using as references.


Any help appreciated, I am building it anyway. But if anyone has a better solution, or any guidance, I'd be pleased to be educated. Thanks, Mike
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  • Former Community Member
    0 Former Community Member
    When idle, a mobile phone does not transmit anything so you wouldn't be able to detect it. As Gerard said, the phone would only send "on its own" a Location Area (LA), or a Routing Area (RA) update message when either moving between areas, or periodically, based on timers defined by the network. If you are a network operator you can request a mobile to perform LA / RA update - something used when looking for missing persons. 


    Leaving all these behind, I am wondering what exactly you expect to detect. In an environment with many phones active ( i.e. outside a Faraway cage and in the real world ) there will be transmissions by several devices, occupying all, or most of the mobile spectrum. You wouldn't be able to detect a transmission from a particular mobile, unless you had a way to filter out all other transmissions ( maybe with the use of a directional antenna? Still you could have multiple transmissions crib the same direction ). It would therefore be very difficult to detect the transmission from a specific mobile, or to even detect when a new mobile enters the area. You can look for " RF fingerprinting " which tries to identify a terminal through the unique imperfections of its RF circuitry. Very challenging area.... 


    Good luck with your research!
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  • Former Community Member
    0 Former Community Member
    When idle, a mobile phone does not transmit anything so you wouldn't be able to detect it. As Gerard said, the phone would only send "on its own" a Location Area (LA), or a Routing Area (RA) update message when either moving between areas, or periodically, based on timers defined by the network. If you are a network operator you can request a mobile to perform LA / RA update - something used when looking for missing persons. 


    Leaving all these behind, I am wondering what exactly you expect to detect. In an environment with many phones active ( i.e. outside a Faraway cage and in the real world ) there will be transmissions by several devices, occupying all, or most of the mobile spectrum. You wouldn't be able to detect a transmission from a particular mobile, unless you had a way to filter out all other transmissions ( maybe with the use of a directional antenna? Still you could have multiple transmissions crib the same direction ). It would therefore be very difficult to detect the transmission from a specific mobile, or to even detect when a new mobile enters the area. You can look for " RF fingerprinting " which tries to identify a terminal through the unique imperfections of its RF circuitry. Very challenging area.... 


    Good luck with your research!
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