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Thread: 9:1 unun question

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    Default 9:1 unun question

    I ordered up some FT114-61 ferrites from Amidon planning to make a 10m 9:1 unun. However, when I excitedly wound it and soldered on a 450ohm resistor to do a sweep with my rigexpert, I was very disappointed in the SWR curve.

    What I did: 2 stacked FT114-61 ferrites with 11 turns (trifilar) of 18AWG solid-core insulated wire. The SWR is at 2:1 at 28MHz, I expected better.

    What I assume (from reading online, I'm not this smart): is that the more turns I use, the lower the self resonance and thus the lower the common-mode impedance at higher frequencies. I assume the higher I go in frequency, the more it acts like a choke.

    What I would like to know: 1st, is what I assume correct? And 2nd, does anyone know the optimum number of turns for 10m given 2 stacked FT114-61 cores?
    Last edited by brandon lind; Fri 19th Apr 2019 at 01:08.

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