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Thread: Simple and legal high distance beacon for tracking stolen things

  1. #1

    Default Simple and legal high distance beacon for tracking stolen things

    Hello.

    I am electronics engineer (digital, analog, but non RF) And I am developing motorcycle GPS/GSM alarm system.

    I really want to incorporate RF beacon, so if someone is jamming GPS or GSM signals, I could track it manually ( as example I can get 1km radius from my unit only based on GSM towers, but i need to locate my unit by using RF beacon)

    Question 1)
    What frequency should I use ?It would be nice if it's legal, also could go far in urban areas to some extent, and would be hard to shield , like it still could work in wan with no windows, also it could be 0.5W since i will have big backup battery of 10.000mAh

    Question 2)
    Simple way to generate this RF signal ( I will have MCU, so i could generate square wave tones of 1khz if i need to) and what antenna should i use? I am constrain to 10cmx8cmx3cm size.

    Question 3)
    It would be nice to be able to make or buy cheap receiver for tracking, any simple options ? ( maybe if it's simple, i could include that tracking with alarm system, so owner could do recovery himself.

    Hope some one could help me with answers, and i wish you good day !

  2. #2

    Default

    PLEASE>>>>> NEVER USE SQUARE WAVES IN RF DESIGN (unless you are using them in mixers with tuned circuit filtering afterwards).. Square waves can be thought of as the combination of many many sine waves at harmonic frequencies added together. This will cause tremendous RF interference and get you in big trouble. Consider those new digital battery chargers, wall warts, or anything designed with an unfiltered switchmode power supply ~ absolute radio chaos and the cause of much frustration to just about every ham. And those devices aren't built with intentional antennas!

    As for "legal", ham is not an option as this is clearly a "for profit" endeavor. You would also have trouble using frequencies that are commonly used for unlicensed public communication as the devices being used (at least in the US) need to be "type (and use) accepted". You will need to contact your local RF coordinating authority (like the FCC in the US) and apply for a business use license and be allocated a frequency.

    I do not believe any thief would take the time to jam GSM or GPS signals. These folks are not going to give a jammer away with every illegal sale (they'd have to or their customers would get ticked off when you come and repo stuff). At best, these thiefs will be using an RF field strength meter to see if the unit is transmitting ~ hence waiting a day or so to remotely activate the beacon.

    Stick with the GSM/GPS approach because, either you will find it, or they will detect the RF and move along (as they are not going to dissect a valuable piece of equipment at the scene of a crime to disable the tracking device). Crooks break off visible antennas (which is where slot antennas kick butt), but they don't carry a toolbox.
    Last edited by brandon lind; Wed 29th Jan 2020 at 16:39.

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