On-line T-match calculators give weird answers???

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by WA7ARK, Oct 15, 2020.

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  1. WA7ARK

    WA7ARK Ham Member QRZ Page

    50 Ohm source at 1.85MHz

    Load to be matched is 23 - j813 Ohms

    I am trying to find required values for the source-side C, the shunt L, and the load-side C for a standard T-network as found in desktop tuners.

    Using most of the on-line calcs, like this one, I get negative values for the capacitors.

    What is going on???

    I do not have SimSmith on this computer.
  2. AC6LA

    AC6LA Ham Member QRZ Page

    With that load at 1.85 MHz a huge inductor is required.



    Dan, AC6LA
    K0UO likes this.
  3. WA7ARK

    WA7ARK Ham Member QRZ Page

    Thanks Dan,

    Using my wife's laptop computer. All I have here is bare-nekkid EzNec.

    That is probably why my friend cannot match his ladder-line fed, non-resonant, 425ft horizontal loop using his desktop tuner on 160m.

    That is a lot of loss in the tuner.

    I am going to add a coil in the loop wire to see if I can cancel some of that reactance before the tuner sees it.

    How far would I have to reduce the -j term so that an normal T-tuner with 25 to 30uH could handle it?

  4. AC6LA

    AC6LA Ham Member QRZ Page

    Assuming a 25 uH coil in the tuner, you can get a 2:1 SWR(50) with a load of 23-j400. If you want 1.2:1 the load jx has to be around -305. At around -j280 you can get an almost perfect match. Of course, that all assumes the tuner acts like a modeled tuner, big assumption.

    If the coil Q is 100 a load of 23-j305 still loses ~32% of the input power.

    Dan, AC6LA
  5. BILLYBOB560

    BILLYBOB560 QRZ Member

    Simple L-network. From the 50-ohm end: shunt 46.15 ohm C followed by a series 837.9 ohm L to the Load.

    Component values at 1.85 MHz: C = 1864 pF, L = 72.1 uH.

    Last edited: Oct 16, 2020
  6. WA7ARK

    WA7ARK Ham Member QRZ Page

    Goal is to fix the antenna so that it can be tuned with the existing tuner; not build a custom tuner...

    I take your point that an L-network will always "work", even when a T-network wont.
  7. BILLYBOB560

    BILLYBOB560 QRZ Member

    Then just add a series ~813 ohm (70 uH) L between the antenna and tuner. All the tuner then needs to do is transform 23 ohms to 50 ohms.

    Last edited: Oct 16, 2020

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