Inductance and Capacitance in Auto Tuner

Discussion in 'General Technical Questions and Answers' started by W9BLF, Feb 12, 2020 at 2:36 AM.

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  1. W9BLF

    W9BLF XML Subscriber QRZ Page

    My auto tuner will not tune 160m even though it is designed to. It is LDG AT-600ProII. I have read the directions and can't determine if I need to increase or decrease the inductance and/or capacitance levels.

    My research on-line hasn't been helpful. Any info would be greatly appreciated. Thanks in advance.

    73 Bryan W9BLF
  2. K7TRF

    K7TRF Premium Subscriber QRZ Page

    What antenna system are you trying to match on 160m?

    The AT 600 pro II can match some loads on 160m, but not any arbitrary match. It's specified to match into real loads in the 6 to 1000 ohm range but if your antenna system presents a highly reactive load the impedance matching range will be lower.
  3. KM3F

    KM3F Ham Member QRZ Page

    TRF is correct.
    You just have a lack of understanding the limits of these devices Look at this spec in your owner manual..
    You need an antenna that presents 1000 ohms or less to enable the tuner to make a match down to 50 ohms.
    Even at 1000 ohms limit, you would have an SWR of 20 to 1 the tuner has to transform to 50 ohms.
  4. SM0GLD

    SM0GLD Ham Member QRZ Page

    That's what exactly what I just recently have experienced with my ATU, it's not the same tuner as yours.
    I found out that it could easily match a capacitive but not an inductive antenna.
    The tuner have enough of series inductance to match a electrically short antenna but not enough of parallel capacitance to match a electrically long antenna.
    On higher frequencies it works fine compensating for the inductive reactance with the available parallel capacitance.

    If your antenna is inductive on 160m it might be that your tuner behaves just as mine.
  5. W9WQA

    W9WQA Ham Member QRZ Page

    i have hi volt mica caps that i have added on the output of a tuner.
    it takes experimenting an you can try adjusting the length to see what you need.
    foldover the ends without cutting. splice on some wire to go long.
    for sure you will learn some stuff!! thats how i did it...
    most important, ignore insults and keep on trying...
  6. WA7ARK

    WA7ARK Ham Member QRZ Page

    If you have a nanoVna or other antenna analyzer that can measure complex impedance, this becomes easy to answer.

    Disconnect your feedline/antenna from the tuner. Connect the analyzer where the tuner was connected, including the ground side. If the tuner is "grounded" only through a coax cable connected to the tuner input, leave that connection intact, and return the ground side of the analyzer to the chassis of the tuner.

    Measure the impedance that the tuner would normally see at your 160m frequency. Say you see something like 8 - j1000 (short antenna, highly capacitive). Use this calculator to see what it takes to convert that to 50 Ohms.


    Your autotuner is likely to be a L-network like L1/C1. Look up the circuit/specs for your auto-tuner to see if it can supply 87uH of L1 inductance. If it doesn't tune, chances are it cannot supply enough inductance. Chances are, adding an external series inductor between the tuner's output and the feedline (only on 160m) will make it so the tuner will auto-tune.
  7. W4HWD

    W4HWD Platinum Subscriber Platinum Subscriber QRZ Page

    Auto tuners have discrete components and tune in combinations of defined values - not continuously like a manual tuner. If it can’t find a combo that matches your antenna, you don’t get to use your antenna on that frequency.
  8. SM0GLD

    SM0GLD Ham Member QRZ Page

    Yes, and tell us the result.
  9. W9BLF

    W9BLF XML Subscriber QRZ Page

    Thank you all for the responses. VERY HELPFUL and I appreciate that. My analyzer is back at mfj for repairs for the second time so when I get it back I will check the impedance and let you know.
    SM0GLD likes this.
  10. KD0CAC

    KD0CAC Ham Member QRZ Page

    You still have not responded to what antenna ?
    What length , hight etc.

    If the antenna is not a close enough match to a 160m , or the installation / environment can affect it , like mentioned above the tuner can not handle / match .

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