Demonstrating an RTL-SDR Based Metal Detector

Over on YouTube user Ancient Discoveries has uploaded a video showing a prototype of his RTL-SDR based metal detector. The metal detector appears to consist of a coiled detection loop antenna powered by an AM transmitter and an RTL-SDR running in Q-branch direct sampling mode.

Ancient discoveries uses SDR# to tune to a low medium wave frequency of around 898 kHz while in direct sampling mode. Then as a piece of metal is moved closer and further from the detection coil the signals on the spectrum move around in correlation with the metals distance. A whining sound just like a real metal detector is also produced by SDR#.

5 comments

  1. Ancient Discoveries

    this is Ancient Discoveries..
    this project is so simple but ı do some improvements next few weeks
    actually in this project ı just attached the rtl doungle antenna but next time will improve it
    ı am going to holiday when ı turn back i will work for 24 hours to finish the project
    25 khz and 6 khz
    my aim is deepest metal detector for coins

  2. Mario

    Innovative uses for the RTL-SDR dongle continue, this one is exceptionally innovative, kudos to the author.

    • Ed, W1AAZ

      I would strongly disagree.

      The commonly available metal detectors for $50, work as follows.

      They are nothing more than 2 simple RF oscillators, with both designed to operate on the same frequency in the LF range. One oscillator is the reference, while other will vary in frequency, because it’s L-C tuned circuit, has it’s inductor located externally, such that when in proximity to metal, will change the inductance and tuned frequency. As a result, when the oscillators are no longer tuned to the same frequency, the difference will produce a audio beat note, that can be heard via headphones or speaker. Obviously, the beat note will vary, depending on the distance the pickup inductor is, from the metal object.

      What’s the innovation in using a RTL-SDR and computer, just to hear the hetrodyned beat note?

      • James

        Ed, your comment is exceptionally simple minded and gives me the impression that you don’t have much experience evaluating innovated ideas. The innovation here is not a simple metal detector, it’s stupid to think that. I immediately see two areas this RTL-SDR metal detector could open up:

        1) Multi-frequency metal detectors (highly sensitive and tunable to individual elements such as zinc, gold, copper, silver, tin, aluminum, etc.)
        2) Ground-penetrating radars (~10 MHz to 2 GHz)

        Lots of potential here for the RTL-SDR thanks to this author.

        • Anonymous

          Unfortunately, you’re not familiar with even the basics concepts of digital signal processing.
          If you were, you should have know better, then to say this.

          Hint – While there are multiple fields of spectroscopy and each uses very different and advanced forms of input spectrum and DSP computer analysis programs.

          Only the uneducated will confuse such an example of SDR capability, with the innovations and science, that has since occurred.

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