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Is it possible to reverse calculation of coax transformation ratio?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by 4L4AGU, Apr 8, 2012.

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  1. 4L4AGU

    4L4AGU Ham Member QRZ Page

    Say we have some antenna, feed with 12 meters of RG-213 coax. Impedance at TX end is say R28-jX 200, frequency is 7.1 mhz. Knowing coax type and it's characteristics, can we calculate it's transformation ratio, so we'll know what is the antenna impedance at feedpoint?
  2. N3OX

    N3OX Ham Member QRZ Page

    Sure, it can be solved for. One easy way to do that is to use VK1OD's calculator:

    Choose your coax type, length, and frequency and choose "Zin" in the drop down "Mismatch" menu instead of "Zload"

    I get a load impedance (at the antenna) of 1.3-j62 for your stated parameters.

  3. 4L4AGU

    4L4AGU Ham Member QRZ Page

    Heheh, I've being used that calculator for ages, but haven't thought about it that way. Thanks. The parameters I provided were just example, no real system.
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