Choosing antenna tuner capacitor

Discussion in 'Radio Circuits, Repair & Performance' started by 9A5DLZ, Feb 16, 2016.

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  1. G4LNA

    G4LNA Ham Member QRZ Page

    That's what I do, but I switch the capacitor bank between the input and output, not a PI but a straightforward L match, I haven't found a problem getting a match on any band. You can see that in my diagram in post #32.
     
  2. 9A5DLZ

    9A5DLZ Ham Member QRZ Page

    G4LNA, I find it difficult to make two coils at exactly the same inductance. For example, two coils that should be 3.2uH are different by 0.05uH. Or maybe 0.01uH. Maybe I am just needlessly obsessing about being perfectly the same?

    I wind them around the pipe, also. And fix them with hot glue.
     
  3. G4LNA

    G4LNA Ham Member QRZ Page

    I think you are worrying unnecessarily, that sort of inductance would be the inductance of the leads, my coils differ by far more than that and it all works fine. Don't forget that there will be the self capacitance and inductance of the matching unit itself, my unit has a self capacitance of 10pf, I'm not sure of the self inductance I haven't measured it, but there will be some, but it is what it is and I don't worry about it.
     
  4. 9A5DLZ

    9A5DLZ Ham Member QRZ Page

    Can anybody recommend some LC meter? I have some chinese meter that I bought from ebay and that one is showing different inductance every time when I measure inductor with it. In the end I had to use theoretical values for inductors, I didn't know which measurement was correct.
     
  5. K7TRF

    K7TRF Premium Subscriber QRZ Page

    For RF inductors and capacitors I use a grid dip meter or antenna analyzer. Build either a tank circuit (for a dip meter) or a series resonant circuit with one known component and the component under test and find the resonant frequency. Use the dip meter in the normal manner with minimal coupling to the tank circuit or use an analyzer to find series resonance (minimum series resistance, not minimum SWR).

    A good LC bridge is great if you're going to do a lot of this kind of work but if you have some stock of fixed capacitors and inductors of known value you can find unknown RF range L and C values pretty easily.

    -Dave
     
  6. G4LNA

    G4LNA Ham Member QRZ Page

    I use my antenna analyser, it measures L and C, they are quite expensive but really handy if you are messing around with antennas.
     
  7. 9A5DLZ

    9A5DLZ Ham Member QRZ Page

    LC bridge like this?

    [​IMG]
     
  8. K7TRF

    K7TRF Premium Subscriber QRZ Page

  9. 9A5DLZ

    9A5DLZ Ham Member QRZ Page

  10. KL7AJ

    KL7AJ Ham Member QRZ Page

    Actually, the inductors don't need to be precisely the same. Even with only moderate matching, you should get a better balance than with any standard balun. I really like this tuner, and I recommend going ahead with it.

    eric
     

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