Magnetic loop antenna controlled by Arduino

This video by Ricardo Caratti demonstrates his method for controlling a Magnetic Loop antenna with an Arduino. The antenna’s tuning capacitor is adjusted using a stepper motor interfaced with the Arduino equipped to read IR commands sent from a compatible IR remote control. This allows the tuning capacitor to rotate clockwise and counterclockwise. Due to the high current demands of the stepper, he used a circuit based on the ULN2003 Darlington transistor array.

Ricardo used the public libraries for irRemote and Stepper.

Regarding the antenna itself, he writes, “My Magnetic Loop antenna was based on models collected on the Internet. In particular, I used the instructions and tips from Alex (PY1AHD), which sells this kind of antenna with a better look than showed in this video.”

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  1. What a great idea. Magnetic loop antennas are pretty amazing, there is nothing comparable for getting rid of RFI, which is a real problem because of all the e-junk we have.. except the advantage (narrow bandwidth) is also a disadvantage (because they have to be tuned..)

    That remote looks suspiciously like one of the leftover remotes from our DVB-T dongles.. Good use for one! Now what would be very cool would be to be able to use the dongle a hf converter, and a raspberry pi together, and control the stepper motor, via lirc or even better, automatically…

  2. Hi OM:
    I was for ideas for tuning capacitors for mag loops and found this url. I was wondering if you would be willing to share some info on the arduino interface.

    Thanks and 73 Ross Bell K7RSB

  3. There are innumerable ways to tune magnetic loops but they can be divided down into methods suitable for both transmitting and receiving and receive only. If you simply want to receive, there is another way to set a remote loop up simply and that is by using a reverse-biased varactor diode. I use an MVAM-109 and a 9 volt battery to “power” it which is kind of a misnomer because the current drain is negligible because the diode is reverse biased. Alternatively, for transmitting you use a variable capacitor. There is a very high voltage and current which can develop across a loop antenna when used for transmitting, so keep that in mind when picking components.

    Maintaining a low resistance and also dissipation factor and Q are important in a way they rarely are in other radio components. Many people make their transmitting loops out of welded copper pipe to maintain a low resistance. Aluminum pipe is probably adequate as long as its thick and the electrical connections are maintained in good condition. Capacitors should be picked by their ability to withstand high voltage. A well made loop antenna can apparently “get out” better than any other antenna its size, it does that because its resonating at its design frequency like a bell.

    The simplest loop antenna doesign is very simple.. Its lust a loop of wire with a variable capacitor connected across a gap in the loop. The coupling to the radio is accomplished by a much smaller coupling loop at the edge of the big loop. Alternatively, the radio can simply be coupled to inductively, that works well for AM radios. Magnetic loops can work up into VHF, but at higher frequencies they are fairly small.

    If they are well made, they are very effective. I use mine for receiving with an upconverter and it allows me to hear all sorts of stuff on the low bands that otherwise would be too weak or buried by noise. A loop can be mounted on something that allows it to swivel and that is very useful because you can tune for the best signal.

    For receiving just a piece of wire will do.

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