Arduino based automatic antenna tuner

Discussion in 'Homebrew and Kit Projects' started by KX4DV, Nov 25, 2018.

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  1. KX4DV

    KX4DV Ham Member QRZ Page

    Has anyone built a automatic tuner based around the Arduino that uses stepper motors to actuate roller inductors and vac caps? I know there's the K3NG controller, but that uses latching relays to tune, due to component size, that limits it to something around 100w max. I have a roller inductor and variable cap that could be used in a L config to handle legal limit. But thus far, I've only seen people using a ramps board to control steppers then interfacing it to a computer to run g-code to move it to predetermined spots.
  2. KW4TI

    KW4TI Ham Member QRZ Page

    This may not be exactly what you're looking for, but I am working on a modular antenna tuner. You can use relays that are capable of higher power with it, for example, Omron G2RL relays that are used in the Elecraft KAT 500 for 500 W power, or possibly higher.


  3. KX4DV

    KX4DV Ham Member QRZ Page

    Thanks, but I'm really looking for something that uses steppers with a roller inductor and variable caps. I'd like something that can handle the power from a linear.
  4. K3KIC

    K3KIC Ham Member QRZ Page

    How much are you willing to invest? What range are you trying to tune? Can you write code?
    If you paired up a Rig Expert to an Arduino along with two stepper motors a coupler and a relay could be done for about $100.
    Could measure SWR with a lower cost circuit but would take some more design work.
    AA7QQ likes this.
  5. AA7QQ

    AA7QQ Ham Member QRZ Page

    Code would have to:
    Lower power of TX (To save components).
    Read Freq data (Not just band data),
    Measure R, X & J
    Determine proper setting of L&C (Unless already pre stored),
    Start L&C movement.
    Arrive at computed results.
    Check R, X & J.
    Refine L&C, if needed.
    Save results to speed up future actions.

    If you would like to see a single stepper system & code, look up " Automatic loop tuner Loftur ". This will give you an idea of what 1 stepper motor requires.
  6. KX4DV

    KX4DV Ham Member QRZ Page

    I already have a JW Miller 2500 auto tuner. Just wanting another high power tuner since I have two stations I work from. (And it'd be nice to not have to manually select the inductance) Just looking for 160m to 10m. I'm not versed in C, that's why I was asking.

    The is a shield, so that'd kinda limit what the arudino could do as far as another shield for the stepper drivers. But maybe there's enough ports to break them out and run together on a mega.

    The antenna I'm planning on using this on is a 160m loop. I'm able to tune all the major bands on it with my 450's LDG tuner. Course this wouldn't help for a linear.

    I know a mag loop antenna can be tuned with a cap alone. Perhaps I could leverage that for this antenna since it's more about adding capacitance to tune for lower bands. (It's 1.0 SWR for 1.82mhz
  7. K3KIC

    K3KIC Ham Member QRZ Page

    The only uses the serial lines. It doesn't need to be plugged in as a shield. An UNO would work fine.

    You could build your own detector for SWR and run CAT control to the rig. But that's more complex software. Not hard for someone who can write code.
  8. KX4DV

    KX4DV Ham Member QRZ Page

    I guess I'll have to try to learn how to code it. From what I've seen of a few demos, people have merely taken a standard swr meter and looked at the reflect to adjust the capacitor.

    Or I could just get a ramps board and use it to just dial the tuner into presets like others have done. I guess that's why no one has gone any deeper than this.
  9. KD1JV

    KD1JV Ham Member QRZ Page

    Yes, I tried to do that. Didn't work very well.

    I made a L tuner, with roller inductor and variable cap. It just kept hunting for a match and would never settle down. Some of that was probably my algorithm, some of that was probably the roller inductor being old and not making great contact with the roller as it adjusted.

    A lot of that was probably the fact I found out later it needed more inductance to match the 160M long wire I was trying to match too. But I didn't find that out until after I gutted the project and turned it back into a manual tuner.

    There's a limit to how fast I could turn the roller inductor and that made for really slow progress. You really need to tweak the inductance, stop and measure, then repeat. I'm not sure I was doing that.

    I had a SWR meter built in and it was suppose to adjust until it found a match under 1:1.5 SWR.

    Here's the sketch I used in text format. Copy and paste into an new Arduino Sketch.

    For the stepper motors, I gutted an old printer and made my own drivers.

    Attached Files:

    Last edited: Dec 2, 2018
    KX4DV likes this.
  10. KX4DV

    KX4DV Ham Member QRZ Page

    Thanks for the sketch. I'll play around with it in the future. Can you tell me any more about your SWR meter? What voltage range did it output?

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